ArticlePDF AvailableLiterature Review

Clinical Endocannabinoid Deficiency Reconsidered: Current Research Supports the Theory in Migraine, Fibromyalgia, Irritable Bowel, and Other Treatment-Resistant Syndromes

Authors:
  • CReDO Science

Abstract and Figures

Medicine continues to struggle in its approaches to numerous common subjective pain syndromes that lack objective signs and remain treatment resistant. Foremost among these are migraine, fibromyalgia, and irritable bowel syndrome, disorders that may overlap in their affected populations and whose sufferers have all endured the stigma of a psychosomatic label, as well as the failure of endless pharmacotherapeutic interventions with substandard benefit. The commonality in symptomatology in these conditions displaying hyperalgesia and central sensitization with possible common underlying pathophysiology suggests that a clinical endocannabinoid deficiency might characterize their origin. Its base hypothesis is that all humans have an underlying endocanna-binoid tone that is a reflection of levels of the endocannabinoids, anandamide (arachidonylethanolamide), and 2-arachidonoylglycerol, their production, metabolism, and the relative abundance and state of cannabinoid receptors. Its theory is that in certain conditions, whether congenital or acquired, endocannabinoid tone becomes deficient and productive of pathophysiological syndromes. When first proposed in 2001 and subsequently, this theory was based on genetic overlap and comorbidity, patterns of symptomatology that could be mediated by the endocannabinoid system (ECS), and the fact that exogenous cannabinoid treatment frequently provided symptomatic benefit. However, objective proof and formal clinical trial data were lacking. Currently, however, statistically significant differences in cerebrospinal fluid anandamide levels have been documented in migrai-neurs, and advanced imaging studies have demonstrated ECS hypofunction in post-traumatic stress disorder. Additional studies have provided a firmer foundation for the theory, while clinical data have also produced evidence for decreased pain, improved sleep, and other benefits to cannabinoid treatment and adjunctive lifestyle approaches affecting the ECS.
Content may be subject to copyright.
REVIEW Open Access
Clinical Endocannabinoid Deficiency Reconsidered:
Current Research Supports the Theory in Migraine,
Fibromyalgia, Irritable Bowel, and Other
Treatment-Resistant Syndromes
Ethan B. Russo*
Abstract
Medicine continues to struggle in its approaches to numerous common subjective pain syndromes that lack ob-
jective signs and remain treatment resistant. Foremost among these are migraine, fibromyalgia, and irritable
bowel syndrome, disorders that may overlap in their affected populations and whose sufferers have all endured
the stigma of a psychosomatic label, as well as the failure of endless pharmacotherapeutic interventions with
substandard benefit. The commonality in symptomatology in these conditions displaying hyperalgesia and cen-
tral sensitization with possible common underlying pathophysiology suggests that a clinical endocannabinoid
deficiency might characterize their origin. Its base hypothesis is that all humans have an underlying endocanna-
binoid tone that is a reflection of levels of the endocannabinoids, anandamide (arachidonylethanolamide), and
2-arachidonoylglycerol, their production, metabolism, and the relative abundance and state of cannabinoid re-
ceptors. Its theory is that in certain conditions, whether congenital or acquired, endocannabinoid tone becomes
deficient and productive of pathophysiological syndromes. When first proposed in 2001 and subsequently, this
theory was based on genetic overlap and comorbidity, patterns of symptomatology that could be mediated by
the endocannabinoid system (ECS), and the fact that exogenous cannabinoid treatment frequently provided
symptomatic benefit. However, objective proof and formal clinical trial data were lacking. Currently, however,
statistically significant differences in cerebrospinal fluid anandamide levels have been documented in migrai-
neurs, and advanced imaging studies have demonstrated ECS hypofunction in post-traumatic stress disorder.
Additional studies have provided a firmer foundation for the theory, while clinical data have also produced ev-
idence for decreased pain, improved sleep, and other benefits to cannabinoid treatment and adjunctive lifestyle
approaches affecting the ECS.
Key words: anandamide; anorexia nervosa; cannabidiol; cannabinoids; depression; endocannabinoids; fibro-
myalgia; Huntington disease; irritable bowel syndrome; migraine; motion sickness; multiple sclerosis; Parkinson
disease; post-traumatic stress disorder; prebiotics; THC
Introduction: Background History and Theory
of Clinical Endocannabinoid Deficiency
The theory of clinical endocannabinoid deficiency
(CED) was presented in 2001 in two publications,
1,2
but more thoroughly explored in 2004
3
in an article
that has subsequently been cited frequently in the lit-
erature.
4
The theory of CED was based on the con-
cept that many brain disorders are associated with
neurotransmitter deficiencies, affecting acetylcholine
in Alzheimer’s disease, dopamine in parkinsonian syn-
dromes, serotonin and norepinephrine in depression,
and that a comparable deficiency in endocannabinoid
PHYTECS, Vashon Island, Washington.
*Address correspondence to: Ethan B. Russo, MD, PHYTECS, 1875 Century Park East, Suite 2250, Los Angeles, CA 90067, E-mail: ethanrusso@comcast.net
ªEthan B. Russo 2016; Published by Mary Ann Liebert, Inc. This Open Access article is distributed under the terms of the Creative Commons License
(http://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work
is properly credited.
Cannabis and Cannabinoid Research
Volume 1.1, 2016
DOI: 10.1089/can.2016.0009
Cannabis and
Cannabinoid Research
154
levels might be manifest similarly in certain disorders
that display predictable clinical features as sequelae of
this deficiency.
All humans possess an underlying endocannabinoid
tone that reflects of levels of anandamide (AEA) and 2-
arachidonoylglycerol (2-AG), the centrally acting endo-
cannabinoids, their synthesis, catabolism, and the relative
density of cannabinoid receptors in the brain. If endo-
cannabinoid function were decreased, it follows that a
lowered pain threshold would be operative, along with
derangements of digestion, mood, and sleep among the
almost universal physiological systems subserved by the
endocannabinoid system (ECS).
5
The CED theory also
posits that such deficienciescouldariseduetogenetic
orcongenitalreasonsorbeacquired due to intercurrent
injury or disease that consequently produces characteris-
tic pathophysiological syndromes with particular symp-
tomatology.
The greatest evidence for CED is present for mi-
graine, fibromyalgia, and irritable bowel syndrome
(IBS).
3
A strong case can be advanced for unifying
pathophysiological trends in the three conditions:
All manifest hyperalgesic states must be clinically
diagnosed based on subjective criteria as all lack
characteristic tissue pathology or easily accessible
objective laboratory findings
All are diagnoses of exclusion that often generate
extensive negative diagnostic work-ups
They display elevated incidence of anxiety and de-
pression (in a chicken vs. egg dilemma) and have
been labeled psychosomatic in origin or worse,
wastebasket diagnoses, at one time or another by
skeptical clinicians
Comorbidity is quite clear in the three diagnoses.
Primary headaches co-occurred in 97% of 201 fibro-
myalgia patients,
6
35.6% of 101 chronic daily head-
ache (transformed migraine) subjects also fit
clinical criteria of fibromyalgia,
7
and 31.6% of IBS
subjects were also diagnosable with fibromyalgia,
while 32% of fibromyalgia patients also fit for IBS
8
While some patients suffer from only one of these
syndromes, lifetime risk to develop another or all
three is quite common (Fig. 1).
An extensive list of other disorders previously cited
that may fall under the CED rubric included
3
neonatal
failure to thrive,
9
cystic fibrosis,
10
causalgia,
11
brachial
plexopathy,
12
phantom limb pain, infantile colic, glau-
coma,
13
dysmenorrhea,
14
hyperemesis gravidarum,
15
unexplained fetal wastage (repetitive miscarriages),
post-traumatic stress disorder (PTSD),
16,17
bipolar dis-
ease,
18
and possibly many others. All display as yet
unfathomed pathophysiological features and remain
treatment resistant. Might their underlying nature
have been missed? Recently, in a seminal article on
the ECS and its optimization,
4
the authors added sup-
port for these and various other conditions.
Materials and Methods
Standard searches were undertaken of the PubMed/
National Library of Medicine database for the listed
keywords and references from pertinent literature for
pertinence to clinical cannabinoid deficiency.
IBS, CED, and the Microbiome–Gut–Brain Axis
IBS, also known as spastic colon, is a functional disor-
der characterized by gastrointestinal (GI) pain, spasm,
discomfort, and altered bowel movements, either pre-
dominantly diarrhea, predominantly constipation, or
alternating between those states. Attacks are highly
correlated with anxiety, but debate continues as to
which incites the other. Individual episodes may be
triggered by some specific foods or dietary indiscre-
tions such as overeating on holidays. While frequently
assessed as a life-long condition,
19
it is clear that signif-
icant gastrointestinal insults such as food poisoning or
antibiotic administration may generate attacks that
persist, often indefinitely. IBS is the most frequent diag-
nosis in gastroenterology practices in the United States,
FIG. 1. Diagram depicting comorbidity of
migraine, fibromyalgia, and irritable bowel
syndrome.
Russo; Cannabis and Cannabinoid Research 2016, 1.1
http://online.liebertpub.com/doi/10.1089/can.2016.0009
155
with prevalence in the Western world of 10–15%.
19
As
an idiopathic disorder, no physical signs are pathogno-
monic, and even diagnostic procedures such as labo-
ratory tests, including those for gluten enteropathy,
colonoscopy, or barium studies, most often fail to
identify other causes,
3
but more formal Rome criteria
have been established.
19
Those authors characterized
the status of IBS as (p. 409) a disorder of unknown or-
igin being treated by agents with an unknown mecha-
nism of action. It has been posited that IBS represents a
visceral hypersensitivity, with features of GI allodynia
and hyperalgesia.
20
A seminal review of the ECS and
its relationship with the GI tract appeared that year.
21
To summarize, GI propulsion, secretion, and inflamma-
tion in the gut are all modulated by the ECS, providing a
rationale for cannabinoids as treatment candidates for
IBS.
22
As examples, GI propulsion is under tonic con-
trol of the ECS,
21
and cannabis was one of the first ef-
fective clinical interventions in the 19th century for
the intense secretory diarrhea associated with cholera,
23
a finding which was more recently validated with mod-
ern methodology.
24
The use, by its sufferers, of cannabis-based agents to
treat IBS has eventuated in large part due to the unfortu-
nate fact that conventional treatment with anticholinergics,
opioids, and antidepressants has been quite suboptimal,
while three dedicated agents have been withdrawn from
certain markets after prior regulatory approval. Two 5-
HT
3
antagonists, alosetron and cilansetron, were asso-
ciated with ischemic colitis, while tegaserod, a 5-HT
4
agonist, produced cardiovascular adverse events.
Additional support for the ECS as a key modulator of
GI function was provided in an examination of circular
muscle fibers from colonoscopic biopsies of surgical spec-
imens from 31 normal patients.
25
AEA colocalized with
cholinergic receptors in normal colon and inhibited the
cholinergic contractile force of circular and longitudi-
nal muscles through a non-CB
1
mechanism or possibly
an alternative cannabinoid mechanism not mediated
by CB
1
or CB
2
. It was posited that inflammatory and
disease states in the gut rendered the ECS more func-
tionally important.
A 3.5-fold elevation in TRPV1-immunoreactive
nerve fibers was observed in biopsies from IBS sufferers
compared with controls ( p<0.0001).
26
The authors
observed (p. 923) that the increased TRPV1 nerve fi-
bers may contribute to visceral hypersensitivity and
pain in IBS and provide a novel therapeutic target.
Thus, a rationale exists for therapeutic interventions
that would boost AEA levels or desensitize TRPV1,
such as cannabidiol (CBD), to treat the condition.
27
Although fatty acid amide hydrolase (FAAH) inhibi-
tion of CBD has been questioned by some, its ability
to raise serum AEA levels was clearly indicated when
administered in high doses to schizophrenic patients.
28
Genetic variation affecting endocannabinoid metabo-
lism was observed in diarrhea-predominant IBS pa-
tients.
29
THC (dronabinol) treatment slowed colonic
transit time in subjects harboring the CNRI rs806378
CT/TT genotype. Subsequently, a statistically significant
association of this gene with colonic transit in IBS with
diarrhea (IBS-D) was demonstrated ( p=0.014).
30
They
observed (p. G559) that CB
1
receptor-related mecha-
nisms modify colonic transit and sensation and may in-
fluence the development of symptoms in Caucasian
patients with IBS, particularly IBS-D.
Unfortunately, while many patient surveys have
touted benefits of cannabinoid treatment of IBS symp-
toms
31
and abundant anecdotal support is evident on
the Internet, little actual clinical work has been accom-
plished. In a randomized controlled trial (RCT) of 52
normal patients taking single doses of 7.5 mg of THC
versus placebo, the drug increased colonic compliance
(p=0.045) and inhibited postprandial colonic tone
(p=0.048) and fasting and postprandial phasic pres-
sure ( p=0.008), with a trend toward relaxation of fast-
ing colon tone ( p=0.096).
32
Another study focused on
visceral sensitivity to rectal distention as measured by a
barostat in normal (N=12) versus IBS (N=10) patients
after administration of THC.
33
No significant differ-
ences were noted, but adverse events were reported in
100% of participants at the 10 mg dosage. A third
small (23 IBS patients) trial of synthetic THC for a
brief interval (2 days) showed no change in transit
time.
29
More formal studies with whole cannabis ex-
tracts would be illuminating.
Additional interventions may be practical on the nu-
tritional front utilizing new knowledge of the utility of
probiotics and prebiotics. A direct effect of Lactobacil-
lus acidophilus NCFM strain through oral administra-
tion to induce CNR2 mRNA expression above that of
resting human HT-29 epithelial cells ( p<0.01) was
demonstrated along with an enhancement of morphine
antinociceptive effect in rats ( p<0.001), which was
inhibited by administration of the CB
2
antagonist,
AM-630 ( p<0.001).
34
A review of human studies of
probiotic supplements to treat IBS revealed that 34/42
trials demonstrated beneficial effects for one or more
end-points or target symptoms (pain, discomfort, bloat-
ing, distention, laboratory parameters).
19
The interplay
Russo; Cannabis and Cannabinoid Research 2016, 1.1
http://online.liebertpub.com/doi/10.1089/can.2016.0009
156
of the microbiome–gut–brain axis in IBS is underscored
by the recent finding that THC altered the microfloral
balance in obese diet-induced obese mice, affecting the
Firmicutes:Bacteroidetes ratio ( p=0.021) and preventing
itsincreaseorweightgaindespiteahigh-fatdiet.
35
Thus,
optimal gut health without pain and with maintenance of
appropriate body weight seems to require a complex in-
terplay between diet, enteric flora, and endocannabinoid
balance.
Experimental models have obvious limitations, and
contrary findings are always possible. A recent study
36
demonstrated in a mouse model of accelerated GI transit
that palmitoylethanolamide, an entourage endocannabi-
noid, indirectly activated CB
1
receptors only under con-
ditions in which AEA or the receptors were upregulated,
not deficient. Furthermore, it is unfortunate that labora-
tory measures of serum or tissue endocannabinoid levels
have not been systematically examined in IBS.
Migraine and CED
Migraine is an extremely prevalent headache syndrome
affecting 14% of Americans, with a 3:1 female:male ratio
and $20 billion annual cost in that country.
37
This au-
thor has previously reported on migraine’s treatment
by cannabis,
1,3,38
and two major reviews have recently
appeared.
39,40
Migraine is far more complex than merely
cranial pain. It has a genetic predilection and female pre-
dominance and presents as a predominantly hemicranial
beating headache associated with unusual associated
manifestations: nausea, photophobia, and phonophobia,
with hormonal and environmental triggers.
The possible relationship of migraine with the ECS
is highlighted by numerous findings. Anandamide
produced serotonin receptor responses consisting of
89% potentiation of 5-HT
1A
and 36% inhibition of
5-HT
2A
,
41
findings that have been associated with
profiles of effective pharmacological migraine inter-
ventions that would seem to support respective activ-
ity in acute and chronic migraine (CM), respectively.
The migraine epiphenomena of photophobia and pho-
nophobia suggest an overactive sensory hyperalgesia,
just the kind of homeostatic imbalance that the ECS
tends to correct in central nervous system (CNS) func-
tion.
5
The periaqueductal gray matter is a putative mi-
graine generator in which AEA is tonically active,
producing analgesia when administered or hyperalge-
sia when CB
1
is pharmacologically blocked.
42
A great deal of additional support for the integral role
of the ECS in migraine pathophysiology has been pro-
vided by a series of investigations linking endocannabi-
noids to the trigeminovascular system, which many
consider to lie at the root of its pathophysiology. The
first experiment
43
resulted in several pertinent findings:
AEA diminished blood vessel dilation in the dura mater
induced by calcitonin gene-related peptide (CGRP)
30%, capsaicin 45%, and nitric oxide (NO) 40%. Addi-
tionally, AEA acted presynaptically to prevent release
of NO by CGRP in dural artery smooth muscle. AEA
also was released in tonic manner and displayed modu-
latory activity in the trigeminovascular system.
A subsequent article focused on vascular phenomena
associated with migraine.
44
AEA caused dose-dependent
dural vessel dilation that was diminished by capsazepine,
aTRPV1antagonist,andbyCGRP
8–37
,aCGRPantago-
nist. (While the vascular effects of this and the prior
study may appear contradictory, it should be noted
that migraine produces vasoconstriction or vasodilation
in different phases and that these are epiphenomena of
the disorder, rather than its etiology.) The concentration
of AEA that produced these findings was far higher than
that required to activate CB
1
.Thissuggeststhepossibility
that repetitive administration with a TRPV1 agonist such
as CBD
27
could conceivably desensitize the receptor
and thus alleviate these pathophysiological mecha-
nisms, much as capsaicin has successfully reduced
peripheral neuropathic pain with regular cutaneous
administration. Capsaicin has even been utilized in-
tranasally as an acute migraine treatment,
45
and it is
thus reasonable to consider CBD as a less noxious al-
ternative desensitizing intervention.
A third publication examined trigeminovascular
neuronal responses
46
with findings that WIN 55,212-
2, a potent CB
1
agonist, inhibited trigeminocervical
complex A and C-fiber afferent activity, which was ab-
rogated by SR141716A, a CB
1
inverse agonist. How-
ever, this finding was only obtained with AEA after
prior TRPV1 blockade by capsazepine. These findings
support possible clinical application of CB
1
-agonists
in migraine and cluster headache, although the authors
warned of psychoactive sequelae of agents such as THC.
In an animal model of migraine,
47
AEA reduced
nitroglycerin-induced neuronal activation in the nucleus
trigeminalis caudalis and area postrema, the latter being
an emetic chemoreceptor. There was likewise an induc-
tion of expression of the immediate early gene transcrip-
tion factor Fos in the hypothalamic paraventricular and
supraoptic nuclei, in the parabrachial nucleus, and in the
brainstem periaqueductal gray matter of the brainstem.
These findings reinforce an important role of the ECS in
generation of migraine episodes.
Russo; Cannabis and Cannabinoid Research 2016, 1.1
http://online.liebertpub.com/doi/10.1089/can.2016.0009
157
Various studies in Italy have focused on the etiolog-
ical relationship of platelets with migraine in affected
patients. In one
48
of the studies, increased function in
AEA membrane transporter and AEA hydrolase (now
known as fatty acid amidohydrolase [FAAH], the en-
zyme that catabolizes AEA) in platelets of women with
migraine without aura was observed in comparison
with patients with episodic tension headache or con-
trols with no headaches. Interestingly, there were no
differences in CB
1
receptor density in the groups,
but AEA hydrolysis was elevated in platelets of mi-
graine sufferers. Consequent decreased serum AEA
levels could theoretically lower the pain threshold in
such patients.
In another study,
49
female and male migraineurs
both displayed lower FAAH and AEA membrane
transporter platelet activity, hypothesized as a possible
adaptive response to CM or a reaction to overuse of
pain killers known as analgesic rebound. An additional
study
50
showed that 2-AG and AEA levels were both
profoundly reduced in the platelets of patients with ep-
isodic migraine without aura (N=20) and CM (N=20)
versus controls (N=20) ( p<0.0001).
Perhaps the strongest evidence of the existence of
CED in migraine or any disorder comes from a study
51
that assayed cerebrospinal fluid (CSF) AEA levels in
15 chronic migraineurs versus 20 controls with a phe-
nomenal statistically significant difference ( p<0.0001)
(Fig. 2). The authors opined concerning what they
termed a system failure in migraine (p. 1387):
Reduced AEA levels in the CSF of CM [chronic migraine] pa-
tients support the hypothesis of the failure of this endogenous
CB [cannabinoid] system in CM, which seems to be related to
increased CGRP and NO production in this pathological con-
dition. This finding might be due to a failure of the inhibitory
role of the endocannabinoid AEA on the trigeminovascular
system activation—.
THC (1–20 lM) and other CB
1
agonists dose-
dependently diminished cortical spreading depression
amplitude, duration, and propagation velocity ( p<0.001)
in a rat brain model, supporting its ability to inhibit
the trigeminovascular in migraine with aura.
52
A clinical study examined 27 medication-overuse
headache patients, a common precipitant of migraine
exacerbation.
53
Before treatment, patients displayed
decreased temporal summation thresholds, increased
pain sensation, and reduced platelet FAAH (the enzyme
that breaks down AEA) expression versus controls.
After medication withdrawal treatment and elimination
of analgesic rebound effects, FAAH activity, and tem-
poral summation thresholds significantly normalized
(both p=0.001), supporting an etiological ECS dys-
function in these patients.
In subsequent experiments in mice,
54
intraperitoneal
injection of nitroglycerine induced mechanical hyperal-
gesia that was almost totally eliminated by FAAH dele-
tion or administration of FAAH inhibitors ( p<0.0001).
Additional supportive data on the migraine-ECS rela-
tionship are derived from genetic investigation. The CB
1
gene, CNR1 mapped to chromosome 6q14-15, was
linked to migraine through haplotypic tagging with
FIG. 2. Anandamide levels in cerebrospinal fluid of chronic migraine patients versus controls, adapted from
data obtained from Sarchielli et al.
51
Russo; Cannabis and Cannabinoid Research 2016, 1.1
http://online.liebertpub.com/doi/10.1089/can.2016.0009
158
high significance ( p=0.008) and indicative of a genetic
effect altering trigeminovascular activation.
55
The stron-
gest linkage was to HT6 haplotype ( p=0.002), which
correlated highly with migraine symptoms of photo-
phobia >nausea >disability. Migraineurs also showed
greater degrees of neuroticism ( p<0.001), depression
(p<0.001), and reported drug/alcohol abuse ( p<
0.005). Of late, many pharmaceutical companies have
pursued development of antibodies aimed at CGRP as
a therapeutic target in migraine prophylaxis,
37
butitre-
mains to be seen whether this represents a more funda-
mental target than strategies focusing on the ECS.
Until recently, only case reports and surveys of use
of THC and cannabis and its effects on migraine have
been published,
31,56
but a more formal observational
trial has been reported
57
from a cannabis-oriented clinic
in the state of Colorado. Among 120 adults with mi-
graine for whom cannabis prophylaxis was recommen-
ded, and of which 67.8% had previously used cannabis,
the frequency of headache diminished from 10.4 to 4.6
attacks per month (p<0.0001) (Fig. 3). Overall, 85.1%
had decreased migraine frequency, with 39.7% reporting
positive effects: prevention of or reduced headache fre-
quency (19.8%) or aborted headache (11.6%) in this
selected and uncontrolled population employing a mix-
ture of administration techniques with unanalyzed but
presumably high-THC cannabis.
It is worth remembering that cannabis was a mainstay
of treatment of migraine in Europe and North America
for a century between 1843 and 1943,
1
similarly sup-
porting claims of a high degree of efficacy of cannabis
treatment in both acute and prophylactic treatments of
migraine. Further study utilizing modern techniques
and standardized preparations with low THC and
higher titers of CBD in proper RCTs is long overdue.
Focus on Fibromyalgia
Fibromyalgia was probably first described by Sir Wil-
liam Gowers
58
as fibrositis, a condition characterized
as soft tissue pain that could wander in the body, and
which was aggravated by overuse. In the 1980s, fibro-
myalgia became the preferred term due to a failure to
identify inflammation or other objective changes in tis-
sue biopsies from affected patients. Formal diagnostic
parameters (Rome Criteria) were established thereafter.
While a recent report indicated the presence of small
fiber neuropathy in a subset of patients with fibromyal-
gia symptoms
59
creating possible diagnostic confusion,
this finding by no means explains all such cases. Fibro-
myalgia is noteworthy for its characteristic painful
nodules dubbed as trigger points that are particularly
prevalent in the shoulder and neck that are frequently
of sufficient severity to limit physical activity. The dis-
order has a clear association with depression and anx-
iety, but debate surrounds the timing and relationship
of these comorbidities. Like migraine, it is more preva-
lent in women and invariably disrupts sleep. The disor-
der remains controversial in some quarters, but it is
nonetheless the most common diagnosis in American
rheumatology practices.
60
Many authorities now posit
a central sensitization consistent with neuropathic pain
at the root of the syndrome.
61
In Italy, it was noted
that fibromyalgia, like migraine, was associated with sec-
ondary hyperalgesia, that is, a lowered threshold to pain
in areas adjacent to the primarily affected parts,
62
for
which the authors suggested pharmacological NMDA
blockade for what they interpreted as a deficit in seroto-
nergic analgesia. That same year, hyperalgesia was ob-
served in association with central endocannabinoid
hypofunction in the spinal cord and that endocannabi-
noids reduced associated hyperalgesia,
63
making the
ECS a prime target and CED a rational explanation.
The authors proposed that cannabinoid treatments
would be indicated for various maladies driven by a
primary afferent barrage, which would include visceral
hyperalgesia (as hypothesized in IBS), allodynia associ-
ated with neuropathic pain states, and reflex sympa-
thetic dystrophy or complex regional pain syndrome.
Cannabisorcannabinoidshavebeenfrequently
utilized by fibromyalgia patients to treat its myriad
FIG. 3. Bar graph of change in migraine
frequency after cannabis treatment, adapted
from data from Rhyne et al.
57
Russo; Cannabis and Cannabinoid Research 2016, 1.1
http://online.liebertpub.com/doi/10.1089/can.2016.0009
159
symptoms. In an uncontrolled trial in nine patients,
THC was administered in doses of 2.5–15 mg a day for
3months.
64
Surprisingly, the ethics committee would
notpermitplacebouseinthestudy. Unfortunately, all
butfourpatientsleftthestudyearlysecondarytoTHC
side effects, but those completing had marked reductions
in subjective pain visual analog scales (VAS) ( p<0.01)
(Fig. 4). No benefits on touch-evoked allodynia, nor
pinprick hyperalgesia, were documented.
Another group examined nabilone, a semisynthetic
THC analog and CB
1
agonist of 10-fold higher poten-
cy.
65
Forty fibromyalgia patients received nabilone
1 mg BID for 4 weeks. Visual analog scales of pain, a
Fibromyalgia Impact Questionnaire, and anxiety scores
were all statistically significantly benefited compared
with placebo ( p<0.02). The effects on sleep were also
assessed with nabilone
66
in 31 patients with doses of
0.5–1 mg at bedtime compared with patients taking
amitriptyline 10–20 mg. Nabilone was superior on an
Insomnia Severity Index, but no benefits on pain, mea-
sure of mood, or quality of life were observed.
Herbal cannabis was utilized in an open-label man-
ner in 28 fibromyalgia patients in comparison with
an equal number of matched control patients
67
in
another report. Two hours after cannabis use, VAS
scores showed a statistically significant ( p<0.001) re-
duction of pain and stiffness, enhancement of relaxa-
tion, and an increase in somnolence and feeling of
well-being. The mental health component summary
score of the Short Form (36) Health Survey (SF-36)
was significantly higher ( p<0.05) in cannabis users
than in nonusers.
Other cannabis-based medicine clinical trials have
been noteworthy in their benefits on symptomatic
reduction allowing sleep (reviewed in Refs.
68,69
),
and the same would likely be obtained in fibromyal-
gia, which displays many features in common with
other causes of peripheral neuropathic pain. A nota-
ble example would be adjunctive use of Sativex
(USAN: nabiximols) in a 5-week RCT in 125 patients
with intractable peripheral neuropathic pain with
allodynia in which it proved superior to placebo
(p=0.00) in Box Scale-11 (BS-11) score change and
reduced dynamic allodynia test scores versus placebo
(p=0.0420).
70
While this degree of benefit is yet to be shown in for-
mal RCTs in fibromyalgia, the court of public opinion
supports its utility. A recent survey on efficacy of three
regulatory body-approved pharmaceutical fibromyal-
gia treatments versus cannabis recently garnered in ex-
cess of 1300 respondents and is available online from
the National Pain Report.
71
Of the approved drugs for fibromyalgia, duloxetine
and milnacipran are mixed serotonin and adrenergic
uptake inhibitors, while pregabalin is an anticonvulsant
drug repurposed to treat neuropathic pain. Results of
the survey (Fig. 5) strongly favor cannabis over the
poorly effective prescription medicines. These results
certainly support an urgent need for more definitive
RCTs of a well-formulated and standardized cannabis-
based medicine in fibromyalgia inasmuch as existing
current medicines with regulatory approval seem to
fall quite short of the mark.
Additional Conditions Suggesting CED
The ECS has been demonstrated to play a key role in
the pathophysiology of motion sickness
72
assessed by
subjecting volunteers to parabolic flight maneuvers
producing microgravity. Seven of 21 adults so tested
developed acute motion sickness with significant re-
ductions in AEA ( p=0.04) and 2-AG ( p=0.01) in
blood. Nausea scores correlated negatively with AEA
(p=0.02), and even CB
1
receptor mRNA gene expres-
sion in leukocytes diminished significantly ( p=0.03)
4 h after exposure in the most adversely affected.
Animal models have clearly established the role of the
ECS in multiple sclerosis (MS).
73
Direct assays of AEA
FIG. 4. Bar graph depicting decreases in pain in
the per-protocol subset of fibromyalgia patients
taking THC, adapted from data from Schley
et al.
64
THC, tetrahydrocannabinol (dronabinol).
Russo; Cannabis and Cannabinoid Research 2016, 1.1
http://online.liebertpub.com/doi/10.1089/can.2016.0009
160
and 2-AG in the CSF of MS patients versus controls con-
firm significant deficits in affected patients, particularly
in secondary progressive cases, confirming an impaired
endocannabinoid system,
74
and affirming the value of
such measurements as a functional disease marker.
In a recent interesting finding assessing central pain
mechanisms in neuropathy due to diabetes, streptozoto-
cin was administered in a rat model that demonstrated
reduced rostroventromedial medullary AEA levels, and
in which the TRPV1 desensitizer, capsaicin, decreased
nociceptive behavioral signs,
75
as well as demonstrating
the central effects of a supposedly peripheral disorder. If
corroborated in human studies, this finding might add
diabetic neuropathy to the growing list of putative endo-
cannabinoid deficiency disorders.
In 2008, a mouse model of Huntington’s disease
(HD) demonstrated a widespread impairment of endo-
cannabinoid function.
76
Subsequently, in the postmor-
tem brains of human patients with HD,
77
a striking loss
of immunoreactivity of CB
1
in putamen and globus
pallidus was demonstrated throughout the time course
of the disorder. The degree of change was much higher
than that for enkephalin or substance P, making CB
1
a
superior marker, even at earlier clinical stages. This loss
of CB
1
was felt to be a potential compensatory response
as it could reduce GABA release in the striatum. A sub-
sequent positron emission tomography (PET) study in
living HD sufferers,
78
employing 18F-MK9470, a CB
1
ligand, demonstrated significant decreases in receptor
availability versus controls ( p<0.0001). These reduc-
tions ranged from 15% in cerebellum up to 25% in
frontal cortex, confirming underactivity of the ECS in
HD that would disrupt neurotransmission and corre-
lated inversely with disease severity.
Direct laboratory measurements were also performed
in untreated Parkinson’s disease (PD) patients, examin-
ing CSF,
79
and demonstrated a doubling of AEA levels
over age-matched controls ( p<0.001), irrespective of
disease stage. The authors posited this as a compensa-
tory mechanism in the striatum of PD patients in an
effort to alleviate dopamine depletion. Subsequently, an-
other study
80
was the first to demonstrate the role of the
ECS in synaptic long-term depression in motor circuits
in PD. The motor deficits present in rodents with dopa-
mine lesions were reversed by combining a D2 agonist
with an endocannabinoid reuptake inhibitor. This find-
ing suggests that progressive dopamine loss in PD in
striatal circuits may decrease endocannabinoid tone and
that the elevations in anandamide in PD patients may
be an attempt to compensate for this loss.
Prior animal research has elucidated the relationship
between the ECS, extinction of aversive memories,
16
and
stress-induced analgesia.
17
This has been supplemented
by additional evidence that stress-induced anxiety is di-
rectly related to central anandamide deficiency in mice.
81
One genetic study in humans has linked genetic var-
iants of CNR1, the CB
1
receptor gene, to fear extinc-
tion mechanisms.
82
Homozygote and heterozygote
G-allele carriers of the gene rs2180619 showed prom-
inent extinction of fear in a virtual reality experiment,
FIG. 5. Efficacy of approved pharmaceuticals compared with cannabis in fibromyalgia according to patient
survey results, adapted from data from National Pain Report.
71
Russo; Cannabis and Cannabinoid Research 2016, 1.1
http://online.liebertpub.com/doi/10.1089/can.2016.0009
161
while A/A homozygotes displayed an absence of fear-
potentiated startle reactions, confirming the role of
the ECS in human fear extinction.
Recent research in humans has clarified the role of
the ECS in post-traumatic stress. Forty-six survivors
of the World Trade Center attacks were studied.
83
Serum 2-AG was significantly reduced in PTSD victims
versus those without PTSD symptoms, especially those
with direct exposure, suggesting a promotion of reten-
tion of aversive memories. A negative relationship was
also noted between AEA levels and intrusive symp-
toms. The authors indicated that research to date sug-
gests a good correlation of lower serum AEA levels to
increased CB
1
receptor binding sites in CNS, as was
demonstrated in a PET study of untreated PTSD pa-
tients.
84
The CB
1
-selective radioligand [
11
C]OMAR
on PET revealed higher volume of distribution (V
T
)
with lower AEA tone in PTSD ( p=0.001) by 19.5%
over healthy controls and 14.5% over traumatized
patients without PTSD. Cortisol levels were lower in
PTSD and trauma patients versus controls and OMAR
V
T
, AEA, and cortisol together correctly identified
85% of PTSD cases. Women had greater CB
1
receptor
availability under basal conditions, suggesting greater
susceptibility to development of PTSD, in accord
with epidemiological observations. Agents increasing
AEA availability were suggested as possible therapy
and such availability might reflect compensatory upre-
gulation as a reaction to reduced endocannabinoid lev-
els. Three excellent recent reviews reinforce these
findings.
85–87
The criticality of ECS function in other psychiatric
syndromes has been evidenced in studies of major de-
pression, which is now thought of less as a failure of
monoamine neurotransmission and more as a disorder
of CNS plasticity with an inflammatory component,
or even as a degenerative disease
88
directly linked to
endocannabinoid deficiency. Additionally, AEA levels
were eightfold higher in CSF of untreated acute schizo-
phrenics than in controls ( p=0.000), and AEA was
negatively correlated with psychotic symptoms ( p=
0.001), representing a compensatory mechanism to
the disorder.
89
Recent clinical trial work supports the
utility of cannabidiol in its treatment.
28
PET was also employed in a study of adult female
anorexia nervosa and bulimia patients,
90
demonstrat-
ing that global CB
1
receptor availability was increased
in anorexia over controls in cortical and subcortical
areas ( p=0.0003), in the insula in both anorexia and
bulimia patients ( p=0.01 and p=0.004, respectively),
and in the inferior frontal and temporal areas in an-
orexia ( p=0.02). The authors related these chronic
upregulations of CB
1
activity to presumed ECS hypoac-
tivity (p. 780). Interestingly, peripheral serum AEA is
elevated in anorexia. Long ago, a single RCT was un-
dertaken in anorexia nervosa in 11 female patients
comparing THC to diazepam in a double-blind cross-
over study.
91
No increased weight gain was noted in
the THC group, but dosing was seemingly excessive
(up to 30 mg daily), as evidenced by paranoid ideation
and loss of control in three patients (27%). More recent
experience would suggest that lower THC dosing with
a cannabis-based preparation, as opposed to pure THC,
might yield different results with prospects for not only
fewer adverse events, but increased efficacy as well.
92–94
Certainly, additional trials are warranted in this com-
mon and difficult clinical context.
Given the current seemingly increased incidence and
recognition of autistic spectrum disorders, it is useful to
note their possible relationship with the ECS. Genes asso-
ciated with these disorders also regulate ECS function:
neuroligin-3 R451C-knockin and neuroligin-3 knockout
mutations in mice impaired tonic endocannabinoid
signaling,
95
with the authors suggesting therapeutic ap-
proaches in the human affliction to address this finding.
Similarly, presynaptic b-neurexins controlled synaptic
signals in excitatory synapses through regulation of post-
synaptic 2-AG production
96
and were said to be essential
for control of tonic endocannabinoid signaling.
Conclusions, Caveats, and Suggestions
for Additional Research on and Treatment of CED
The current review has examined the concept of CED
and presented more than a decade of supportive objec-
tive evidence. However, certain caveats are necessary.
One is that contradictory findings are not only possible
but also common. This is due, in part, to the often re-
ciprocal relationships between the two major endocan-
nabinoids, AEA and 2-AG, as expansively demonstrated
in a current review
87
: Anandamide is most often the
tonic signaling agent of the ECS and regulator of syn-
aptic transmission, while 2-arachidonoylglycerol acts
as a phasic signal activator in neuronal depolarization
and mediator of synaptic plasticity. Thus, discordant
levels of the two endocannabinoids may frequently be en-
countered. Additionally, while CED may be harmful,
excesses clearly are, as well, with obvious examples of
obesity, metabolic syndrome, and hepatic fibrosis.
97
Aside from the evidence of depressed AEA levels in
the CSF of migraine sufferers
51
and the other examples
Russo; Cannabis and Cannabinoid Research 2016, 1.1
http://online.liebertpub.com/doi/10.1089/can.2016.0009
162
presented here, there has been little direct objective ev-
idence of the CED theory in patients until quite re-
cently. Additional investigations in a similar vein to
assess endocannabinoid levels in the serum or spinal
fluid of migraine, IBS, and fibromyalgia versus controls
would be illuminating. Anatomic and physiological
scanning techniques (e.g., fMRI, PET) are not yet capa-
ble of producing real-time direct assessments of endo-
cannabinoid levels in living patients, but hopefully
research will soon allow this type of screening assess-
ment in health and disease. Similarly, genomic testing
has produced great strides in elucidating the mutations
responsible for many congenital conditions, but has
not yet fully plumbed the depths of regulation of
gene function that may well underlie the putative
CED conditions discussed herein.
RCTs of CED conditions are certainly well justified
on the basis of current data and should replace the cur-
rent largely uncontrolled black market experiments
that desperate patients with these afflictions are con-
temporaneously forced to undertake in their quest for
relief of their symptoms.
Various strategies to treat CED conditions are possi-
ble. A direct approach with CB
1
agonists must recog-
nize the fact that the ECS operates as a homeostatic
regulator that sometimes requires a gentle pharmaco-
logical nudge, rather than a forceful shove, by synthetic
full agonists. Thus, small doses of a weak partial agonist
(e.g., THC) should be considered, which would not in-
duce tolerance and may jump-start the ECS. Even THC
alone is poorly tolerated or appreciated by patients,
98
and standardized whole cannabis extracts that contain
additional synergistic and buffering components, such
as CBD and cannabis terpenoids, are certainly prefera-
ble.
93
Alternatively, FAAH inhibitors will also raise AEA
levels, but only CBD among them has achieved current
legal commercial market availability. Pharmaceutical ap-
proaches affecting endocannabinoid transport or its ge-
netic regulation would also hold promise. Beyond drug
interventions, a growing body of knowledge supports
the realistic goal that lifestyle approaches should be in-
tegral to the treatment of CED; specifically, low-impact
aerobic regimens have demonstrated beneficial ef-
fects on endocannabinoid function,
99
and as discussed
above, dietary manipulations with probiotics and
prebiotics may ameliorate not only IBS symptoms
but also the entire spectrum of CED conditions. Ulti-
mately, multimodality approaches are most likely to
be fruitful in treatment of these common yet difficult
clinical challenges.
Acknowledgment
The assistance of Interlibrary Loan of Mansfield Library,
University of Montana, is gratefully acknowledged.
Author Disclosure Statement
No competing financial interests exist.
References
1. Russo EB. Hemp for headache: an in-depth historical and scientific review
of cannabis in migraine treatment. J Cannabis Ther. 2001;1:21–92.
2. Russo EB. Handbook of psychotropic herbs: a scientific analysis of herbal
remedies for psychiatric conditions. Haworth Press: Binghamton, NY,
2001.
3. Russo EB. Clinical endocannabinoid deficiency (CECD): can this con-
cept explain therapeutic benefits of cannabis in migraine, fibromyalgia,
irritable bowel syndrome and other treatment-resistant conditions?
Neuroendocrinol Lett. 2004;25:31–39.
4. McPartland JM, Guy GW, Di Marzo V. Care and feeding of the endocan-
nabinoid system: a systematic review of potential clinical interventions
that upregulate the endocannabinoid system. PLoS One. 2014;9:e89566.
5. Pacher P, Kunos G. Modulating the endocannabinoid system in human
health and disease—successes and failures. FEBS J. 2013;280:1918–1943.
6. Nicolodi M, Sicuteri F. Fibromyalgia and migraine, two faces of the same
mechanism. In: Recent Advances in Tryptophan Research (Filippini GA,
ed). Plenum Press: New York, 1996, pp. 373–379.
7. Peres MF, Young WB, Kaup AO, et al. Fibromyalgia is common in patients
with transformed migraine. Neurology. 2001;57:1326–1328.
8. Sperber AD, Atzmon Y, Neumann L, et al. Fibromyalgia in the irritable
bowel syndrome: studies of prevalence and clinical implications. Am J
Gastroenterol. 1999;94:3541–3546.
9. Fride E, Bregman T, Kirkham TC. Endocannabinoids and food intake:
newborn suckling and appetite regulation in adulthood. Exp Biol Med
(Maywood). 2005;230:225–234.
10. Fride E. Cannabinoids and cystic fibrosis: a novel approach. J Cannabis
Ther. 2002;2:59–71.
11. Notcutt W, Price M, Miller R, et al. Initial experiences with medicinal ex-
tracts of cannabis for chronic pain: results from 34 ‘‘N of 1’’ studies.
Anaesthesia. 2004;59:440–452.
12. Berman JS, Symonds C, Birch R. Efficacy of two cannabis based medicinal
extracts for relief of central neuropathic pain from brachial plexus avul-
sion: results of a randomised controlled trial. Pain. 2004;112:299–306.
13. Jarvinen T, Pate D, Laine K. Cannabinoids in the treatment of glaucoma.
Pharmacol Ther. 2002;95:203–220.
14. Russo E. Cannabis treatments in obstetrics and gynecology: a historical
review. J Cannabis Ther. 2002;2:5–35.
15. Westfall R, Janssen P, Lucas P, et al. Survey of medicinal cannabis use
among childbearing women: patterns of its use in pregnancy and retro-
active self-assessment of tis efficacy against ‘morning sickness’. Com-
plement Ther Clin Pract. 2006;12:27–33.
16. Marsicano G, Wotjak CT, Azad SC, et al. The endogenous cannabinoid sys-
tem controls extinction of aversive memories. Nature. 2002;418:530–534.
17. Hohmann AG, Suplita RL, Bolton NM, et al. An endocannabinoid mech-
anism for stress-induced analgesia. Nature. 2005;435:1108–1112.
18. Ashton CH, Moore PB, Gallagher P, et al. Cannabinoids in bipolar affec-
tive disorder: a review and discussion of their therapeutic potential.
J Psychopharmacol. 2005;19:293–300.
19. Clarke G, Cryan JF, Dinan TG, et al. Review article: probiotics for the
treatment of irritable bowel syndrome—focus on lactic acid bacteria.
Aliment Pharmacol Ther. 2012;35:403–413.
20. Holzer P. Gastrointestinal afferents as targets of novel drugs for the
treatment of functional bowel disorders and visceral pain. Eur J Phar-
macol. 2001;429:177–193.
21. Pertwee RG. Cannabinoids and the gastrointestinal tract. Gut.
2001;48:859–867.
22. Di Carlo G, Izzo AA. Cannabinoids for gastrointestinal diseases: potential
therapeutic applications. Expert Opin Investig Drugs. 2003;12:39–49.
23. O’Shaughnessy WB. On the preparations of the Indian hemp, or gunjah
(Cannabis indica); their effects on the animal system in health, and their
Russo; Cannabis and Cannabinoid Research 2016, 1.1
http://online.liebertpub.com/doi/10.1089/can.2016.0009
163
utility in the treatment of tetanus and other convulsive diseases. Trans
Med Phys Soc Bengal. 1838–1840;71–102:421–461.
24. Izzo AA, Capasso F, Costagliola A, et al. An endogenous cannabinoid tone
attenuates cholera toxin-induced fluid accumulation in mice. Gastroen-
terology. 2003;125:765–774.
25. Smid SD, Bjorklund CK, Svensson KM, et al. The endocannabinoids
anandamide and 2-arachidonoylglycerol inhibit cholinergic contractility
in the human colon. Eur J Pharmacol. 2007;575:168–176.
26. Akbar A, Yiangou Y, Facer P, et al. Increased capsaicin receptor TRPV1-
expressing sensory fibres in irritable bowel syndrome and their correla-
tion with abdominal pain. Gut. 2008;57:923–929.
27. Bisogno T, Hanus L, De Petrocellis L, et al. Molecular targets for canna-
bidiol and its synthetic analogues: effect on vanilloid VR1 receptors and
on the cellular uptake and enzymatic hydrolysis of anandamide. Br J
Pharmacol. 2001;134:845–852.
28. Leweke FM, Piomelli D, Pahlisch F, et al. Cannabidiol enhances ananda-
mide signaling and alleviates psychotic symptoms of schizophrenia.
Transl Psychiatry. 2012;2:e94.
29. Wong BS, Camilleri M, Eckert D, et al. Randomized pharmacodynamic and
pharmacogenetic trial of dronabinol effects on colon transit in irritable
bowel syndrome-diarrhea. Neurogastroenterol Motil. 2012;24:358-e169.
30. Camilleri M, Kolar GJ, Vazquez-Roque MI, et al. Cannabinoid receptor 1
gene and irritable bowel syndrome: phenotype and quantitative traits.
Am J Physiol Gastrointest Liver Physiol. 2013;304:G553–G560.
31. Ware MA, Adams H, Guy GW. The medicinal use of cannabis in the UK:
results of a nationwide survey. Int J Clin Pract. 2005;59:291–295.
32. Esfandyari T, Camilleri M, Busciglio I, et al. Effects of a cannabinoid re-
ceptor agonist on colonic motor and sensory functions in humans: a
randomized, placebo-controlled study. Am J Physiol Gastrointest Liver
Physiol. 2007;293:G137–G145.
33. Klooker TK, Leliefeld KE, Van Den Wijngaard RM, et al. The cannabinoid
receptor agonist delta-9-tetrahydrocannabinol does not affect visceral
sensitivity to rectal distension in healthy volunteers and IBS patients.
Neurogastroenterol Motil. 2011;23:30–35, e2.
34. Rousseaux C, Thuru X, Gelot A, et al. Lactobacillus acidophilus modulates
intestinal pain and induces opioid and cannabinoid receptors. Nat Med.
2007;13:35–37.
35. Cluny NL, Keenan CM, Reimer RA, et al. Prevention of diet-induced obe-
sity effects on body weight and gut microbiota in mice treated chroni-
cally with delta9-tetrahydrocannabinol. PLoS One. 2015;10:e0144270.
36. Capasso R, Orlando P, Pagano E, et al. Palmitoylethanolamide normalizes
intestinal motility in a model of post-inflammatory accelerated transit:
involvement of CB(1) receptors and TRPV1 channels. Br J Pharmacol.
2014;171:4026–4037.
37. Underwood E. A shot at migraine. Science. 2016;351:116–119.
38. Russo E. Cannabis for migraine treatment: the once and future prescrip-
tion? An historical and scientific review. Pain. 1998;76:3–8.
39. Baron EP. Comprehensive review of medicinal marijuana, cannabinoids,
and therapeutic implications in medicine and headache: what a long
strange trip it’s been. Headache. 2015;55:885–916.
40. Greco R, Gasperi V, Maccarrone M, et al. The endocannabinoid system
and migraine. Exp Neurol. 2010;224:85–91.
41. Boger DL, Patterson JE, Jin Q. Structural requirements for 5-HT2A and
5-HT1A serotonin receptor potentiation by the biologically active lipid
oleamide. Proc Natl Acad Sci U S A. 1998;95:4102–4107.
42. Walker JM, Hohmann AG, Martin WJ, et al. The neurobiology of canna-
binoid analgesia. Life Sci. 1999;65:665–673.
43. Akerman S, Kaube H, Goadsby PJ. Anandamide is able to inhibit trigem-
inal neurons using an in vivo model of trigeminovascular-mediated
nociception. J Pharmacol Exp Ther. 2003;309:56–63.
44. Akerman S, Kaube H, Goadsby PJ. Anandamide acts as a vasodilator of
dural blood vessels in vivo by activating TRPV1 receptors. Br J Pharmacol.
2004;142:1354–1360.
45. Fusco BM, Barzoi G, Agro F. Repeated intranasal capsaicin applications to
treat chronic migraine. Br J Anaesth. 2003;90:812.
46. Akerman S, Holland PR, Goadsby PJ. Cannabinoid (CB1) receptor activa-
tion inhibits trigeminovascular neurons. J Pharmacol Exp Ther.
2007;320:64–71.
47. Greco R, Mangione AS, Sandrini G, et al. Effects of anandamide in mi-
graine: data from an animal model. J Headache Pain. 2011.
48. Cupini LM, Bari M, Battista N, et al. Abnormal degradation of endocan-
nabinoids in migrainous women. Cephalalgia. 2003;23:684.
49. Cupini LM, Costa C, Sarchielli P, et al. Degradation of endocannabinoids
in chronic migraine and medication overuse headache. Neurobiol Dis.
2008;30:186–189.
50. Rossi C, Pini LA, Cupini ML, et al. Endocannabinoids in platelets of chronic
migraine patients and medication-overuse headache patients: relation
with serotonin levels. Eur J Clin Pharmacol. 2008;64:1–8.
51. Sarchielli P, Pini LA, Coppola F, et al. Endocannabinoids in chronic mi-
graine: CSF findings suggest a system failure. Neuropsychopharmacol-
ogy. 2007;32:1384–1390.
52. Kazemi H, Rahgozar M, Speckmann EJ, et al. Effect of cannabinoid
receptor activation on spreading depression. Iran J Basic Med Sci.
2012;15:926–936.
53. Perrotta A, Arce-Leal N, Tassorelli C, et al. Acute reduction of anandamide-
hydrolase (FAAH) activity is coupled with a reduction of nociceptive
pathways facilitation in medication-overuse headache subjects after
withdrawal treatment. Headache. 2012;52:1350–1361.
54. Nozaki C, Markert A, Zimmer A. Inhibition of FAAH reduces nitroglycerin-
induced migraine-like pain and trigeminal neuronal hyperactivity in mice.
Eur Neuropsychopharmacol. 2015;25:1388–1396.
55. Juhasz G, Lazary J, Chase D, et al. Variations in the cannabinoid receptor
1 gene predispose to migraine. Neurosci Lett. 2009;461:116–120.
56. el-Mallakh RS. Marijuana and migraine. Headache. 1987;27:442–443.
57. Rhyne DN, Anderson SL, Gedde M, et al. Effects of medical marijuana on
migraine headache frequency in an adult population. Pharmacotherapy.
2016;36:505–510.
58. Gowers WR. A lecture on lumbago: its lessons and analogues. Br Med J.
1904;1:117–121.
59. Caro XJ, Winter EF. The role and importance of small fiber neuropathy in
fibromyalgia pain. Curr Pain Headache Rep. 2015;19:55.
60. Bennett RM. Rational management of fibromyalgia. Rheum Dis Clin North
Am. 2002;28:xiii–xv.
61. Bennett RM. The rational management of fibromyalgia patients. Rheum
Dis Clin North Am. 2002;28:181–199, v.
62. Nicolodi M, Volpe AR, Sicuteri F. Fibromyalgia and headache. Failure
of serotonergic analgesia and N-methyl-D-aspartate-mediated neu-
ronal plasticity: their co mmon clues. Cephalalgia. 1998;18(Suppl 21):
41–44.
63. Richardson JD, Aanonsen L, Hargreaves KM. Hypoactivity of the spinal
cannabinoid system results in NMDA-dependent hyperalgesia. J Neuro-
sci. 1998;18:451–457.
64. Schley M, Legler A, Skopp G, et al. Delta-9-THC based monotherapy in
fibromyalgia patients on experimentally induced pain, axon reflex flare,
and pain relief. Curr Med Res Opin. 2006;22:1269–1276.
65. Skrabek RQ, Galimova L, Ethans K, et al. Nabi lone for the treatment of pain
in fibromyalgia. J Pain. 2008;9:164–173.
66. Ware MA, Fitzcharles MA, Joseph L, et al. The effects of nabilone on sleep
in fibromyalgia: results of a randomized controlled trial. Anesth Analg.
2010;110:604–610.
67. Fiz J, Duran M, Capella D, et al. Cannabis use in patients with fibromyalgia:
effect on symptoms relief and health-related quality of life. PLoS One.
2011;6:e18440.
68. Russo EB, Guy GW, Robson PJ. Cannabis, pain, and sleep: lessons from
therapeutic clinical trials of Sativex, a cannabis-based medicine. Chem
Biodivers. 2007;4:1729–1743.
69. Russo EB, Hohmann AG. Role of cannabinoids in pain management. In:
Comprehensive Treatment of Chronic Pain by Medical, Interventional and
Behavioral Approaches (Deer T, Gordin V, eds.). Springer: New York, 2013,
pp. 181–197.
70. Nurmikko TJ, Serpell MG, Hoggart B, et al. Sativex successfully treats
neuropathic pain characterised by allodynia: a randomised, double-blind,
placebo-controlled clinical trial. Pain. 2007;133:210–220.
71. National Pain Report. Marijuana rated most effective for treating fibro-
myalgia. National Pain Report, 2014. Available at: http://nationalpainreport
.com/marijuana-rated-most-effective-for-treating-fibromyalgia-8823638
.html
72. Chouker A, Kaufmann I, Kreth S, et al. Motion sickness, stress and the
endocannabinoid system. PLoS One. 2010;5:e10752.
73. Baker D, Pryce G, Croxford JL, et al. Endocannabinoids control spasticity in
a multiple sclerosis model. FASEB J. 2001;15:300–302.
74. Di Filippo M, Pini LA, Pelliccioli GP, et al. Abnormalities in the cerebro-
spinal fluid levels of endocannabinoids in multiple sclerosis. J Neurol
Neurosurg Psychiatry. 2008;79:1224–1229.
Russo; Cannabis and Cannabinoid Research 2016, 1.1
http://online.liebertpub.com/doi/10.1089/can.2016.0009
164
75. Silva M, Martins D, Charrua A, et al. Endovanilloid control of pain modu-
lation by the rostroventromedial medulla in an animal model of diabetic
neuropathy. Neuropharmacology. 2016;107:49–57.
76. Bisogno T, Martire A, Petrosino S, et al. Symptom-related changes of
endocannabinoid and palmitoylethanolamide levels in brain areas of
R6/2 mice, a transgenic model of Huntington’s disease. Neurochem Int.
2008;52:307–313.
77. Allen KL, Waldvogel HJ, Glass M, et al. Cannabinoid (CB(1)), GABA(A) and
GABA(B) receptor subunit changes in the globus pallidus in Huntington’s
disease. J Chem Neuroanat. 2009;37:266–281.
78. Van Laere K, Casteels C, Dhollander I, et al. Widespread decrease of type 1
cannabinoid receptor availability in Huntington disease in vivo. J Nucl
Med. 2010;51:1413–1417.
79. Pisani A, Fezza F, Galati S, et al. High endogenous cannabinoid levels in
the cerebrospinal fluid of untreated Parkinson’s disease patients. Ann
Neurol. 2005;57:777–779.
80. Kreitzer AC, Malenka RC. Endocannabinoid-mediated rescue of striatal
LTD and motor deficits in Parkinson’s disease models. Nature.
2007;445:643–647.
81. Bluett RJ, Gamble-George JC, Hermanson DJ, et al. Central anandamide
deficiency predicts stress-induced anxiety: behavioral reversal through
endocannabinoid augmentation. Transl Psychiatry. 2014;4:e408.
82. Heitland I, Klumpers F, Oosting RS, et al. Failure to extinguish fear and
genetic variability in the human cannabinoid receptor 1. Transl Psychia-
try. 2012;2:e162.
83. Hill MN, Bierer LM, Makotkine I, et al. Reductions in circulating endo-
cannabinoid levels in individuals with post-traumatic stress disorder fol-
lowing exposure to the World Trade Center attacks.
Psychoneuroendocrinology. 2013;38:2952–2961.
84. Neumeister A, Normandin MD, Pietrzak RH, et al. Elevated brain can-
nabinoid CB1 receptor avai lability in post-traumatic stress diso rder:
a positron emission tomography study. Mol Psychiatry. 2013;18:
1034–1040.
85. Neumeister A, Seidel J, Ragen BJ, et al. Translational evidence for a role of
endocannabinoids in the etiology and treatment of posttraumatic stress
disorder. Psychoneuroendocrinology. 2015;51:577–584.
86. Gabbay FE, Choi KH, Wynn GH, et al. The role of endoncannbinoid function
in posttraumatic stress disorder: modulation the risk phenotype and ren-
dering effects of trauma. In: Cannabinoids in Neurologic and Mental Dis-
ease (Fattore L, ed.). Academic Press: London, 2015, pp. 247–288.
87. Morena M, Patel S, Bains JS, et al. Neurobiological interactions between
stress and the endocannabinoid system. Neuropsychopharmacology.
2016;41:80–102.
88. Hill MN, Gorzalka BB. Is there a role for the endocannabinoid system in
the etiology and treatment of melancholic depression? Behav Pharmacol.
2005;16:333–352.
89. Giuffrida A, Leweke FM, Gerth CW, et al. Cerebrospinal anandamide levels
are elevated in acute schizophrenia and are inversely correlated with
psychotic symptoms. Neuropsychopharmacology. 2004;29:2108–2114.
90. Gerard N, Pieters G, Goffin K, et al. Brain type 1 cannabinoid receptor
availability in patients with anorexia and bulimia nervosa. Biol Psychiatry.
2011;70:777–784.
91. Gross H, Ebert MH, Faden VB, et al. A double-blind trial of delta 9-
tetrahydrocannabinol in primary anorexia nervosa. J Clin Psychophar-
macol. 1983;3:165–171.
92. Portenoy RK, Ganae-Motan ED, Allende S, et al. Nabiximols for opioid-
treated cancer patients with poorly-controlled chronic pain: a random-
ized, placebo-controlled, graded-dose trial. J Pain. 2012;13:438–449.
93. Russo EB. Taming THC: potential cannabis synergy and
phytocannabinoid-terpenoid entourage effects. Br J Pharmacol.
2011;163:1344–1364.
94. Russo EB, Mead AP, Sulak D. Current status and future of cannabis re-
search. Clin Researcher. 2015:58–63.
95. Foldy C, Malenka RC, Sudhof TC. Autism-associated neuroligin-3 muta-
tions commonly disrupt tonic endocannabinoid signaling. Neuron.
2013;78:498–509.
96. Anderson GR, Aoto J, Tabuchi K, et al. Beta-neurexins control neural cir-
cuits by regulating synaptic endocannabinoid signaling. Cell.
2015;162:593–606.
97. Pacher P, Kunos G. Cardiovascular, metabolic, liver kidney and inflam-
matory disorders. In: Handbook of Cannabis (Pertwee R, ed.). Oxford
University Press: Oxford, United Kingdom, 2014, pp. 564–581.
98. Calhoun SR, Galloway GP, Smith DE. Abuse potential of dronabinol
(Marinol). J Psychoactive Drugs. 1998;30:187–196.
99. RaichlenDA,FosterAD,GerdemanGL,etal.Wiredtorun:exercise-
induced endocannabinoid signaling in humans and cursorial mammals
with implications for the ‘runner’s high’. J Exp Biol. 2012;215:1331–
1336.
Cite this article as: Russo EB (2016) Clinical endocannabinoid defi-
ciency reconsidered: current research supports the theory in mi-
graine, fibromyalgia, irritable bowel and other treatment-resistant
syndromes, Cannabis and Cannabinoid Research 1:1, 154–165, DOI:
10.1089/can.2016.0009.
Abbreviations Used
2-AG ¼2-arachidonoylglycerol
5-HT ¼5-hydroxytryptamine (serotonin)
AEA ¼arachidonylethanolamide (anandamide)
BS-11 ¼Box Scale-11
CB ¼cannabinoid
CB
1
/CB
2
¼cannabinoid receptor 1 or 2
CBD ¼cannabidiol
CED ¼clinical endocannabinoid deficiency
CGRP ¼calcitonin gene-related peptide
CM ¼chronic migraine
CNS ¼central nervous system
CSF ¼cerebrospinal fluid
ECS ¼endocannabinoid system
FAAH ¼fatty acid amide hydrolase
fMRI ¼functional magnetic resonance imaging
GABA ¼gamma-aminobutyric acid
GI ¼gastrointestinal
HD ¼Huntington’s disease
IBS ¼irritable bowel syndrome
IBS-D ¼irritable bowel syndrome with diarrhea
MS ¼multiple sclerosis
NMDA ¼N-methyl-D-aspartate
NO ¼nitric oxide
PD ¼Parkinson’s disease
PET ¼positron emission tomography
PTSD ¼post-traumatic stress disorder
RCT ¼randomized controlled trial
SF-36 ¼Short Form (36) Health Survey
THC ¼tetrahydrocannabinol (dronabinol)
TRPV ¼transient receptor potential vanilloid receptor
VAS ¼visual analog scale
Publish in Cannabis and Cannabinoid Research
-Immediate, unrestricted online access
-Rigorous peer review
-Compliance with open access mandates
-Authors retain copyright
-Highly indexed
-Targeted email marketing
liebertpub.com/can
Russo; Cannabis and Cannabinoid Research 2016, 1.1
http://online.liebertpub.com/doi/10.1089/can.2016.0009
165
... ECB biomarkers also are present for nonneuropathic pain conditions: bladder pain (81), fibromyalgia (78,82), cold pain sensitivity (83), osteoarthritis (84), knee pain (85), and back pain (86). Clinical Cannabinoid Deficiency Syndrome has been linked to migraines, neuromuscular pain, and gastrointestinal disorders (87). ...
Article
Full-text available
Chronic pain affects ~10–20% of the U.S. population with an estimated annual cost of $600 billion, the most significant economic cost of any disease to-date. Neuropathic pain is a type of chronic pain that is particularly difficult to manage and leads to significant disability and poor quality of life. Pain biomarkers offer the possibility to develop objective pain-related indicators that may help diagnose, treat, and improve the understanding of neuropathic pain pathophysiology. We review neuropathic pain mechanisms related to opiates, inflammation, and endocannabinoids with the objective of identifying composite biomarkers of neuropathic pain. In the literature, pain biomarkers typically are divided into physiological non-imaging pain biomarkers and brain imaging pain biomarkers. We review both types of biomarker types with the goal of identifying composite pain biomarkers that may improve recognition and treatment of neuropathic pain.
... In addition, eCBs may act autocrinally on CB1 and interact with other neurotransmitters, such as dopamine, regulating intrinsic neuronal activity [20]. In 2006, Russo suggested the "clinical endocannabinoid deficiency" (CED), as low levels of eCBs had been reported in painful conditions such as fibromyalgia and migraine [21]. Evidence from several preclinical studies seems to indicate that the dysregulation of ECS, with reduced eCB activity, plays a role in migraine. ...
Article
Full-text available
The endocannabinoid system (ECS) influences many biological functions, and hence, its pharmacological modulation may be useful for several disorders, such as migraine. Preclinical studies have demonstrated that the ECS is involved in the modulation of trigeminal excitability. Additionally, clinical data have suggested that an endocannabinoid deficiency is associated with migraine. Given these data, phytocannabinoids, as well as synthetic cannabinoids, have been tried as migraine treatments. In this narrative review, the current clinical evidence of potential ECS involvement in migraine pathogenesis is summarized. Furthermore, studies exploring the clinical effects of phytocannabinoids and synthetic cannabinoids on migraine patients are reviewed.
... Uusimpien tutkimusten pohjalta Ethan Russo, neurologiaan erikoistunut lääkäri ja tutkimuksen ja kehittämisen ohjaaja kansainvälisestä kannabis kannabinoidi-instituutista (ICCI) sekä monet muut alan tutkijat teorisoivat, että endokannabinoidijärjestelmän tarkoituksena onkin ylläpitää tasapainoa ke-hon eri järjestelmissä hidastamalla ja nopeuttamalla prosesseja tarpeen mukaan (Russo 2015). Hänen mukaansa monet sairaudet johtuvatkin endokannabinoidijärjestelmän puutostiloista (Russo 2016). ...
Thesis
Full-text available
There was a demand for marketing material and knowledge base for the cannabinoid products that the client Hamppumaa is reselling. The goal was to clarify the effects, possibilities, production, refining, markets and media conversation. There was not any finnish clarification about the cannabinoid industry so we wanted to translate what cannabinoid products are and what are their possibilities. The implementation method was a literature review on scientific studies and media articles. The results clarified the effects of cannabinoids, production related legislation in Finland and abroad, different processing methods and refining possibilities. Also including observations on cannabinoid markets and recent media conversations. Conclusion stated that cannabinoid products have market potential, health effects, changing legislative sitution and industrial possibilities in Finland.
Article
Background: It is known from medical practise that patients and physicians can have positive experiences with little-researched and unapproved interventions. Under certain circumstances, effects even go beyond the placebo effect. Method: Based on casuistics of chronic pain patients, the question of whether self-medication in the context of a good doctor-patient relationship can optimize the efficacy of cannabinoids and reduce dose and undesirable side effects is investigated. Using medicinal cannabis as an example, a new view on self-medication and medical support is proposed. Results: The casuistics show that daily requirements (average of approximately 75 mg) for Δ9tetrahydocannabinol (THC) doses can be reduced. An unaccompanied and risky self-medication can be transformed into an effective therapy with significantly less medical cannabis. The approach consists of tracing the self-medication that has taken place to date and picking up the patient where he has "discovered" something for himself. The specific mode of action of cannabis in chronic diseases can be explained by mechanisms in the endocannabinoid system. Cannabinoids relieve patients in the context of stress, anxiety and depression, which are always involved in chronic diseases. In their physical as well as psychological sensations, patients are strengthened and eventually guided into self-efficacy. Conclusions: If the patient has "discovered" cannabis as medicine for himself and can draw on positive experiences, something very powerful can emerge. In addition to the specific effects demonstrated by studies, there are non-specific effects or contextual factors at work that tend to be neglected in evidence-based medicine. These non-specific effects include, above all, those factors through which a patient gives a (subjective) meaning to a specific intervention. A new view on self-medication and medical support in chronic diseases is needed.
Article
Full-text available
OBJECTIVES: This study examines the concept of clinical endocannabinoid deficiency (CECD), and the prospect that it could underlie the pathophysiology of migraine, fibromyalgia, irritable bowel syndrome, and other functional conditions alleviated by clinical cannabis. METHODS: Available literature was reviewed, and literature searches pursued via the National Library of Medicine database and other resources. RESULTS: Migraine has numerous relationships to endocannabinoid function. Anandamide (AEA) potentiates 5-HT1A and inhibits 5-HT2A receptors supporting therapeutic efficacy in acute and preventive migraine treatment. Cannabinoids also demonstrate dopamine-blocking and anti-inflammatory effects. AEA is tonically active in the periaqueductal gray matter, a migraine generator. THC modulates glutamatergic neurotransmission via NMDA receptors. Fibromyalgia is now conceived as a central sensitization state with secondary hyperalgesia. Cannabinoids have similarly demonstrated the ability to block spinal, peripheral and gastrointestinal mechanisms that promote pain in headache, fibromyalgia, IBS and related disorders. The past and potential clinical utility of cannabis-based medicines in their treatment is discussed, as are further suggestions for experimental investigation of CECD via CSF examination and neuro-imaging. CONCLUSION: Migraine, fibromyalgia, IBS and related conditions display common clinical, biochemical and pathophysiological patterns that suggest an underlying clinical endocannabinoid deficiency that may be suitably treated with cannabinoid medicines.
Article
Full-text available
Objective: Acute administration of cannabinoid CB1 receptor agonists, or the ingestion of cannabis, induces short-term hyperphagia. However, the incidence of obesity is lower in frequent cannabis users compared to non-users. Gut microbiota affects host metabolism and altered microbial profiles are observed in obese states. Gut microbiota modifies adipogenesis through actions on the endocannabinoid system. This study investigated the effect of chronic THC administration on body weight and gut microbiota in diet-induced obese (DIO) and lean mice. Methods: Adult male DIO and lean mice were treated daily with vehicle or THC (2mg/kg for 3 weeks and 4 mg/kg for 1 additional week). Body weight, fat mass, energy intake, locomotor activity, whole gut transit and gut microbiota were measured longitudinally. Results: THC reduced weight gain, fat mass gain and energy intake in DIO but not lean mice. DIO-induced changes in select gut microbiota were prevented in mice chronically administered THC. THC had no effect on locomotor activity or whole gut transit in either lean or DIO mice. Conclusions: Chronic THC treatment reduced energy intake and prevented high fat diet-induced increases in body weight and adiposity; effects that were unlikely to be a result of sedation or altered gastrointestinal transit. Changes in gut microbiota potentially contribute to chronic THC-induced actions on body weight in obesity.
Article
Full-text available
Serious investigators of fibromyalgia (FM) realize the profound implications of finding features of small fiber neuropathy (SFN) in this disorder. For the first time, an easily reproducible and generally agreed upon, peripheral tissue lesion has been reported from multiple investigative centers. Understanding how this discovery relates to other features of FM, and how one might utilize it to better comprehend, and care for, afflicted patients' painful complaints remains a challenge, however. In this article we review how the SFN seen in FM may be placed in context, and suggest how such a tissue abnormality might be used to better understand the pathophysiology of FM, and plan for its effective treatment. We also suggest how finding SFN in FM implies the need for continued focused research within the area of neuropathic disease in FM.
Article
The involvement of transient receptor vanilloid type-1 (TRPV1) channels in pain modulation by the brain remains understudied. The rostroventromedial medulla (RVM) plays a key role in conveying to the spinal cord pain modulatory influences triggered in higher brain centres, with co-existence of inhibitory (antinociceptive) and facilitatory (pronociceptive) effects. In spite of some reports of TRPV1 expression in the RVM, it remains unknown if endovanilloid signalling plays a direct role in local pain modulation. Here we used a model of diabetic neuropathy, the streptozotocin (STZ)-diabetic rat, to study the role of endovanilloid signalling in RVM-mediated pain modulation during chronic pain. Four weeks after diabetes induction, the levels of TRPV1 mRNA and fatty acid amide hydrolase (FAAH), a crucial enzyme for endovanilloid catabolism, in the RVM of STZ-diabetic rats were higher than control. The RVM of STZ-diabetic rats presented decreased levels of several TRPV1 endogenous ligands, namely anandamide (AEA), palmitoylethanolamide (PEA) and oleoylethanolamide (OEA). Administration of capsaicin (a TRPV1 agonist) into the RVM decreased nociceptive behavioural responses in the inflammatory phase of the formalin test (phase 2). These findings suggest that diabetic neuropathy induces plastic changes of RVM endovanilloid signaling, indicating that TRPV1 may be a putative target for pain modulation in this chronic pain condition.
Article
Study Objective No clinical trials are currently available that demonstrate the effects of marijuana on patients with migraine headache; however, the potential effects of cannabinoids on serotonin in the central nervous system indicate that marijuana may be a therapeutic alternative. Thus, the objective of this study was to describe the effects of medical marijuana on the monthly frequency of migraine headache. DesignRetrospective chart review. SettingTwo medical marijuana specialty clinics in Colorado. PatientsOne hundred twenty-one adults with the primary diagnosis of migraine headache who were recommended migraine treatment or prophylaxis with medical marijuana by a physician, between January 2010 and September 2014, and had at least one follow-up visit. Measurements and ResultsThe primary outcome was number of migraine headaches per month with medical marijuana use. Secondary outcomes were the type and dose of medical marijuana used, previous and adjunctive migraine therapies, and patient-reported effects. Migraine headache frequency decreased from 10.4 to 4.6 headaches per month (p<0.0001) with the use of medical marijuana. Most patients used more than one form of marijuana and used it daily for prevention of migraine headache. Positive effects were reported in 48 patients (39.7%), with the most common effects reported being prevention of migraine headache with decreased frequency of migraine headache (24 patients [19.8%]) and aborted migraine headache (14 patients [11.6%]). Inhaled forms of marijuana were commonly used for acute migraine treatment and were reported to abort migraine headache. Negative effects were reported in 14 patients (11.6%); the most common effects were somnolence (2 patients [1.7%]) and difficulty controlling the effects of marijuana related to timing and intensity of the dose (2 patients [1.7%]), which were experienced only in patients using edible marijuana. Edible marijuana was also reported to cause more negative effects compared with other forms. Conclusion The frequency of migraine headache was decreased with medical marijuana use. Prospective studies should be conducted to explore a cause-and-effect relationship and the use of different strains, formulations, and doses of marijuana to better understand the effects of medical marijuana on migraine headache treatment and prophylaxis.
Article
Millions dread the onset of migraine headaches, which strike roughly 12% of the world's population at least once per year. Existing treatments can only head off migraines after they start, and don't work for many people. On the horizon, however, is a new class of drugs that many scientists believe can stop migraines at their root. Four pharmaceutical companies are racing to complete advanced clinical trials of antibody drugs that block the activity of a molecule called calcitonin gene-related peptide, or CGRP, which spikes during migraine attacks. The discovery of CGRP may also help to solve the centuries-old puzzle of what triggers a migraine's complex neurological events.