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REVIEW
Cannabidiol as a Potential Treatment for Anxiety Disorders
Esther M. Blessing
1
&Maria M. Steenkamp
1
&Jorge Manzanares
1,2
&
Charles R. Marmar
1
#The American Society for Experimental NeuroTherapeutics, Inc. 2015
Abstract Cannabidiol (CBD), a Cannabis sativa constituent,
is a pharmacologically broad-spectrum drug that in recent
years has drawn increasing interest as a treatment for a range
of neuropsychiatric disorders. The purpose of the current re-
view is to determine CBD’s potential as a treatment for
anxiety-related disorders, by assessing evidence from preclin-
ical, human experimental, clinical, and epidemiological stud-
ies. We found that existing preclinical evidence strongly sup-
ports CBD as a treatment for generalized anxiety disorder,
panic disorder, social anxiety disorder, obsessive–compulsive
disorder, and post-traumatic stress disorder when adminis-
tered acutely; however, few studies have investigated chronic
CBD dosing. Likewise, evidence from human studies sup-
ports an anxiolytic role of CBD, but is currently limited to
acute dosing, also with few studies in clinical populations.
Overall, current evidence indicates CBD has considerable po-
tential as a treatment for multiple anxiety disorders, with need
for further study of chronic and therapeutic effects in relevant
clinical populations.
Keywords Cannabidiol .Endocannabinoids .Anxiety .
Generalized anxiety disorder .Post-traumatic stress disorder
Introduction
Fear and anxiety are adaptive responses essential to coping
with threats to survival. Yet excessive or persistent fear may
be maladaptive, leading to disability. Symptoms arising from
excessive fear and anxiety occur in a number of neuropsychi-
atric disorders, including generalized anxiety disorder (GAD),
panic disorder (PD), post-traumatic stress disorder (PTSD),
social anxiety disorder (SAD), and obsessive–compulsive dis-
order (OCD). Notably, PTSD and OCD are no longer classi-
fied as anxiety disorders in the recent revision of the Diagnos-
tic and Statistical Manual of Mental Disorders-5; however,
excessive anxiety is central to the symptomatology of both
disorders. These anxiety-related disorders are associated with
a diminished sense of well-being, elevated rates of unemploy-
ment and relationship breakdown, and elevated suicide risk
[1–3]. Together, they have a lifetime prevalence in the USA
of 29 % [4], the highest of any mental disorder, and constitute
an immense social and economic burden [5,6].
Currently available pharmacological treatments include sero-
tonin reuptake inhibitors, serotonin–norepinephrine reuptake in-
hibitors, benzodiazepines, monoamine oxidase inhibitors, tricy-
clic antidepressant drugs, and partial 5-hydroxytryptamine (5-
HT)
1A
receptor agonists. Anticonvulsants and atypical antipsy-
chotics are also used to treat PTSD. These medications are asso-
ciated with limited response rates and residual symptoms, partic-
ularly in PTSD, and adverse effects may also limit tolerability
and adherence [7–10]. The substantial burden of anxiety-related
disorders and the limitations of current treatments place a high
priority on developing novel pharmaceutical treatments.
Cannabidiol (CBD) is a phytocannabinoid constituent of
Cannabis sativa that lacks the psychoactive effects of Δ
9-
tet-
rahydrocannabinol (THC). CBD has broad therapeutic prop-
erties across a range of neuropsychiatric disorders, stemming
from diverse central nervous system actions [11,12]. In recent
*Esther M. Blessing
esther.blessing@nyumc.org
1
New York University School of Medicine, New York, NY, USA
2
Instituto de Neurociencias de Alicante, Universidad Miguel
Hernández and Consejo Superior deInvestigaciones Científicas,
Alicante, Spain
Neurotherapeutics
DOI 10.1007/s13311-015-0387-1
years, CBD has attracted increasing interest as a potential
anxiolytic treatment [13–15]. The purpose of this review is
to assess evidence from current preclinical, clinical, and epi-
demiological studies pertaining to the potential risks and ben-
efits of CBD as a treatment for anxiety disorders.
Methods
A search of MEDLINE (PubMed), PsycINFO, Web of Science
Scopus, and the Cochrane Library databases was conducted for
English-language papers published up to 1 January 2015, using
the search terms Bcannabidiol^and Banxiety^or Bfear^or
Bstress^or Banxiety disorder^or Bgeneralized anxiety disorder^
or Bsocial anxiety disorder^or Bsocial phobia^or Bpost-trau-
matic stress disorder^or Bpanic disorder^or Bobsessive com-
pulsive disorder^. In total, 49 primary preclinical, clinical, or
epidemiological studies were included. Neuroimaging studies
that documented results from anxiety-related tasks, or resting
neural activity, were included. Epidemiological or clinical stud-
ies that assessed CBD’s effects on anxiety symptoms, or the
potential protective effects of CBD on anxiety symptoms in-
duced by cannabis use (where the CBD content of cannabis is
inferred via a higher CBD:THC ratio), were included.
CBD Pharmacology Relevant to Anxiety
General Pharmacology and Therapeutic Profile
Cannabis sativa,aspeciesoftheCannabis genus of flowering
plants, is one of the most frequently used illicit recreational
substances in Western culture. The 2 major phyto- cannabinoid
constituents with central nervous system activity are THC, re-
sponsible for the euphoric and mind-altering effects, and CBD,
which lacks these psychoactive effects. Preclinical and clinical
studies show CBD possesses a wide range of therapeutic prop-
erties, including antipsychotic, analgesic, neuroprotective, anti-
convulsant, antiemetic, antioxidant, anti-inflammatory, antiar-
thritic, and antineoplastic properties (see [11,12,16–19]for
reviews). A review of potential side effects in humans found
that CBD was well tolerated across a wide dose range, up to
1500 mg/day (orally), with no reported psychomotor slowing,
negative mood effects, or vital sign abnormalities noted [20].
CBD has a broad pharmacological profile, including inter-
actions with several receptors known to regulate fear and
anxiety-related behaviors, specifically the cannabinoid type
1 receptor (CB
1
R), the serotonin 5-HT
1A
receptor, and the
transient receptor potential (TRP) vanilloid type 1 (TRPV1)
receptor [11,12,19,21]. In addition, CBD may also regulate,
directly or indirectly, the peroxisome proliferator-activated
receptor-γ, the orphan G-protein-coupled receptor 55, the e-
quilibrative nucleoside transporter, the adenosine transporter,
additional TRP channels, and glycine receptors [11,12,19,
21]. In the current review of primary studies, the following
receptor-specific actions were found to have been investigated
as potential mediators of CBD’s anxiolytic action: CB
1
R,
TRPV1 receptors, and 5-HT
1A
receptors. Pharmacology rele-
vant to these actions is detailed below.
The Endocannabinoid System
Following cloning of the endogenous receptor for THC,
namely the CB
1
R, endogenous CB
1
R ligands, or
Bendocannabinoids^(eCBs) were discovered, namely anan-
damide (AEA) and 2-arachidonoylglycerol (reviewed in [22]).
The CB
1
R is an inhibitory G
i/o
protein-coupled receptor that is
mainly localized to nerve terminals, and is expressed on both
γ-aminobutryic acid-ergic and glutamatergic neurons. eCBs
are fatty acid derivatives that are synthesized on demand in
response to neuronal depolarization and Ca
2+
influx, via
cleavage of membrane phospholipids. The primary mecha-
nism by which eCBs regulate synaptic function is retrograde
signaling, wherein eCBs produced by depolarization of the
postsynaptic neuron activate presynaptic CB
1
Rs, leading to
inhibition of neurotransmitter release [23]. The BeCB system^
includes AEA and 2-arachidonoylglycerol; their respective
degradative enzymes fatty acid amide hydroxylase (FAAH)
and monoacylglycerol lipase; the CB
1
R and related CB
2
re-
ceptor (the latter expressed mainly in the periphery); as well as
several other receptors activated by eCBs, including the
TRPV1 receptor, peroxisome proliferator-activated
receptor-γ, and G protein-coupled 55 receptor, which func-
tionally interact with CB
1
R signaling (reviewed in [21,24]).
Interactions with the TRPV1 receptor, in particular, appear to
be critical in regulating the extent to which eCB release leads
to inhibition or facilitation of presynaptic neurotransmitter re-
lease [25]. The TRPV1 receptor is a postsynaptic cation chan-
nel that underlies sensation of noxious heat in the periphery,
with capsacin (hot chili) as an exogenous ligand. TRPV1 re-
ceptors are also expressed in the brain, including the amygdala,
periaqueductal grey, hippocampus, and other areas [26,27].
The eCB system regulates diverse physiological functions,
including caloric energy balance and immune function [28].
The eCB system is also integral to regulation of emotional
behavior, being essential to forms of synaptic plasticity that
determine learning and response to emotionally salient, par-
ticularly highly aversive events [29,30]. Activation of CB
1
Rs
produces anxiolytic effects in various models of uncondi-
tioned fear, relevant to multiple anxiety disorder symptom
domains (reviewed in [30–33]). Regarding conditioned fear,
the effect of CB
1
R activation is complex: CB
1
R activation
may enhance or reduce fear expression, depending on brain
locus and the eCB ligand [34]; however, CB
1
R activation
potently enhances fear extinction [35], and can prevent
fear reconsolidation. Genetic manipulations that impede
Blessing et al.
CB
1
R activation are anxiogenic [35], and individuals with
eCB system gene polymorphisms that reduce eCB tone—
for example, FAAH gene polymorphisms—exhibit physio-
logical, psychological, and neuroimaging features consis-
tent with impaired fear regulation [36]. Reduction of
AEA–CB
1
R signaling in the amygdala mediates the
anxiogenic effects of corticotropin-releasing hormone
[37], and CB
1
R activation is essential to negative feedback
of the neuroendocrine stress response, and protects against
the adverse effects of chronic stress [38,39]. Finally,
chronic stress impairs eCB signaling in the hippocampus
and amygdala, leading to anxiety [40,41], and people
with PTSD show elevated CB
1
R availability and reduced
peripheral AEA, suggestive of reduced eCB tone [42].
Accordingly, CB
1
R activation has been suggested as a tar-
get for anxiolytic drug development [15,43,44]. Proposed
agents for enhancing CB
1
R activation include THC, which
is a potent and direct agonist; synthetic CB
1
R agonists; FAAH
inhibitors and other agents that increase eCB availability, as
well as nonpsychoactive cannabis phytocannabinoids, includ-
ing CBD. While CBD has low affinity for the CB
1
R, it func-
tions as an indirect agonist, potentially via augmentation of
CB
1
R constitutional activity, or via increasing AEA through
FAAH inhibition (reviewed in [21]).
Several complexities of the eCB system may impact upon
the potential of CBD and other CB
1
R-activating agents to serve
as anxiolytic drugs. First, CB
1
R agonists, including THC and
AEA, have a biphasic effect: low doses are anxiolytic, but
higher doses are ineffective or anxiogenic, in both preclinical
models in and humans (reviewed in [33,45]). This biphasic
profile may stem from the capacity of CB
1
R agonists to
also activate TRPV1 receptors when administered at a high,
but not low dose, as demonstrated for AEA [46]. Activation
of TRPV1 receptors is predominantly anxiogenic, and thus a
critical balance of eCB levels, determining CB1 versus TRPV1
activation, is proposed to govern emotional behavior [27,47].
CBD acts as a TRPV1 agonist at high concentrations, poten-
tially by interfering with AEA inactivation [48]. In addition to
dose-dependent activation of TRPV1 channels, the anxiogenic
versus anxiolytic balance of CB
1
R agonists also depends on
dynamic factors, including environmental stressors [33,49].
5-HT
1A
Receptors
The 5-HT
1A
receptor (5-HT
1A
R) is an established anxiolytic
target. Buspirone and other 5-HT
1A
R agonists are approved
for the treatment of GAD, with fair response rates [50]. In
preclinical studies, 5-HT
1A
R agonists are anxiolytic in animal
models of general anxiety [51], prevent the adverse effects of
stress [52], and enhance fear extinction [53]. Both pre- and
postsynaptic 5-HT
1A
Rs are coupled to various members of the
G
i/o
protein family. They are expressed on serotonergic neurons
in the raphe, where they exert autoinhibitory function, and
various other brain areas involved in fear and anxiety
[54,55]. Mechanisms underlying the anxiolytic effects
of 5-HT
1A
R activation are complex, varying between
both brain region, and pre- versus postsynaptic locus,
and are not fully established [56]. While in vitro studies
suggest CBD acts as a direct 5-HT
1A
R agonist [57],
in vivo studies are more consistent with CBD acting
as an allosteric modulator, or facilitator of 5-HT
1A
signaling [58].
Preclinical Evaluations
Generalized Anxiety Models
Relevant studies in animal models are summarized in chro-
nological order in Table 1. CBD has been studied in a wide
range of animal models of general anxiety, including the
elevated plus maze (EPM), the Vogel-conflict test (VCT),
and the elevated T maze (ETM). See Table 1for the anxi-
olytic effect specific to each paradigm. Initial studies of
CBD in these models showed conflicting results: high
(100 mg/kg) doses were ineffective, while low (10 mg/kg)
doses were anxiolytic [59,60]. When tested over a wide
range of doses in further studies, the anxiolytic effects of
CBD presented a bell-shaped dose–response curve, with an-
xiolytic effects observed at moderate but not higher doses
[61,90]. All further studies of acute systemic CBD without
prior stress showed anxiolytic effects or no effect [62,65],
the latter study involving intracerebroventricular rather than
the intraperitoneal route. No anxiogenic effects of acute sys-
temic CBD dosing in models of general anxiety have yet
been reported. As yet, few studies have examined chronic
dosing effects of CBD in models of generalized anxiety.
Campos et al. [66] showed that in rat, CBD treatment for
21 days attenuated inhibitory avoidance acquisition [83].
Long et al. [69] showed that, in mouse, CBD produced
moderate anxiolytic effects in some paradigms, with no ef-
fects in others.
Anxiolytic effects of CBD in models of generalized anxiety
have been linked to specific receptor mechanisms and brain
regions. The midbrain dorsal periaqueductal gray (DPAG) is
integral to anxiety, orchestrating autonomic and behavioral
responses to threat [91], and DPAG stimulation in humans
produces feelings of intense distress and dread [92]. Microin-
jection of CBD into the DPAG produced anxiolytic effects in
the EPM, VGC, and ETM that were partially mediated by
activation of 5-HT
1A
Rs but not by CB
1
Rs [65,68]. The bed
nucleus of the stria terminalis (BNST) serves as a principal
output structure of the amygdaloid complex to coordinate
sustained fear responses, relevant to anxiety [93]. Anxiolytic
effects of CBD in the EPM and VCT occurred upon microin-
jection into the BNST, where they depended on 5-HT
1A
R
Cannabidiol as a Potential Treatment for Anxiety Disorders
Tab l e 1 Preclinical studies
Study Animal Route Dose Model Effect Receptor Involvement
Silveira Filho et al. [59]WR i.p. 100 mg/kg,
acute
GSCT No effect NA
Zuardi et al. [60]WR i.p. 10mg/kg,
acute
CER Anxiolytic NA
Onaivi et al. [61] ICR mice i.p. 0.01, 0.10, 0.50,1.00,2.50,5.00,
10.00,50.00, 100.00 mg/kg, acute
EPM Anxiolytic Effects ↓by IP flumazenil,
unchanged by naloxone
Guimaraes et al. [61]WR i.p. 2.5,5.0,10.0 and
20.0 mg/kg, acute
EPM Anxiolytic NA
Moreira et al. [62]WR i.p. 2.5,5.0and10.0 mg/kg, acute VCT Anxiolytic Effect unchanged by IP
flumazenil
Resstel et al. [63]WR i.p. 10 mg/kg, acute CFC Anxiolytic NA
Campos et al. [64] WR dlPAG 15.0, 30.0, 60.0 nmol/0.2 μl, acute EPM Anxiolytic Both effects ↓by intra-dlPAG
WAY100635 but not
intra-dlPAG AM251
VCT Anxiolytic
Bitencourt et al. [65]WR i.c.v. 2.0 μg/μl
5 min before extinction, acute
CFC
extinction
Anxiolytic Extinction effect ↓by
SR141716A but not
capsazepineEPM before and
24 h after CFC
No effect before CFC
Anxiolytic following CFC
Campos et al. [66]WR dlPAG 30, 60 mg/kg, acute EPM Anxiolytic Intra-dlPAG capsazepine
renders 60 mg/kg anxiolytic
Resstel et al. [67]WR i.p. 1,10 or 20 mg/kg, acute RS Anxiolytic,
↓Pressor
↓Tachycardia
All effects ↓by systemic
WAY100635
EPM 24 h
following RS
Anxiolytic
Soares et al. [68] WR dlPAG 15, 30 or 60nmol, acute ETM Anxiolytic
Panicolytic
All effects ↓by intra-dlPAG
WAY100635 but not AM251
PAG E-stim Panicolytic
Long et al. [69] C57BL/6 J mice i.p. 1, 5, 10, 50mg/kg, chronic, daily/21 d EPM No effect NA
L-DT 1 mg/kg
anxiolytic
SI No effect
OF 50 mg/kg anxiolytic
Lemos et al. [70]WR i.p.
PL
IL
10mg/kg IP, 30nmol intra-PL and
intra-IL, acute
CFC IP and PL anxiolytic IL
anxiogenic
NA
Casarotto et al. [71] C57BL/6 J mice i.p. 15, 30, and 60 mg/kg,
acute, or subchronic, daily/7 d
MBT Anticompulsive Effect ↓by IP AM251 but not
WAY100635
Gomes et al. [72] WR BNST 15, 30, and 60 nmol, acute EPM Anxiolytic Both effects ↓by intra BNST
WAY100635VCT Anxiolytic
Granjeiro et a l. [73] WR Intracisternal 15, 30, and 60 nmol, acute RS Anxiolytic, ↓Pressor ↓Tachycardia NA
EPM 24 h after RS Anxiolytic
Deiana et al. [74]SM i.p.
Oral
120mg/kg, acute MBT Anticompulsive NA
Uribe-Marino et al. [75]SM i.p. 0.3,3.0,30.0mg/kg, acute PS Panicolytic NA
Blessing et al.
Tab l e 1 (continued)
Study Animal Route Dose Model Effect Receptor Involvement
Stern et al. [76]WR i.p. 3,10, 30 mg/kg
immediately after retrieval,
acute
Reconsolidation blockade Anxiolytic
1and7doldfearmemories
disrupted
Effect ↓by AM251 but not
WAY100635
Campos et al. [77]WR i.p. 5mg/kg, subchronic, daily/7 d EPM following PS Anxiolytic Effects ↓by IP WAY100635
Hsiao et al. [78]WR CeA1μg/μl REM sleep time ↓REM sleep suppression NA
EPM Anxiolytic
OF Anxiolytic
Gomes et al. [79]WR BNST15,30,60nmol, acute CFC Anxiolytic Both effects ↓by intra-BNST
WAY100635
El Batsh et al. [80] LE-H R i.p. 10mg/kg, chronic,
daily/14 d
CFC Anxiogenic NA
Campos et al. [81] C57BL/6 mice i.p. 30mg/kg2 hafterCUS,
chronic daily/14 d
EPM Anxiolytic Both effects ↓by AM251
NSF Anxiolytic
Do Monte et al. [82] L-E HR IL 1 μgor0.4μg/0.2 μl
5 min before extinction
daily/4 d
Extinction of CFC Anxiolytic Effect ↓by IP rimonabant
Campos et al. [83]Rat i.p. 5mg/kg, chronic,
daily/21 d
ETM Anxiolytic
Panicolytic
Panicolytic effect ↓by
intra-dlPAG WAY100635
Almeida et al. [84]Rat i.p. 1, 5, 15 mg/kg, acute SI Anxiolytic NA
Gomes et al. [85]WR BNST30 and 60 nmol, acute RS Anxiogenic
↑Tachydardia
Effect ↓by WAY100635
Twardowschy et al. [86]SM i.p. 3mg/kg, acute PS Panicolytic Effects ↓by IP WAY100635
Focaga et al. [87] WR PL 15, 30, 60 nmol, acute EPM Anxiogenic All effects ↓by intra PL
WAY100635
Anxiolytic EPM effect
post-RS ↓by IP metyrapone
EPM after RS Anxiolytic
CFC Anxiolytic
Nardo et al. [88]SM i.p. 30 mg/kg, acute MBT Anticompulsive NA
da Silva et al. [89]WR SNpr 5μg/0.2μl GABA
A
blockade
in dlSC
Panicolytic Both effects ↓by AM251
Effective doses are in bold
Receptor specific agents: AM251 = cannabinoid receptor type 1 (CB
1
R) inverse agonist; WAY100635 = 5-hydroxytryptamine 1A antagonist; SR141716A = CB
1
R antagonist; rimonabant = CB
1
R
antagonist; capsazepine = transient receptor potential vanilloid type 1 antagonist; naloxone = opioid antagonist; flumazenil = GABA
A
receptor antagonist
Anxiolytic effects in models used: CER = reduced fear response; CFC = reduced conditioned freezing; CFC extinction = reduced freezing following extinction training; EPM = reduced % time in open arm;
ETM = decreased inhibitory avoidance; L-DT = increased % time in light; VCT = increased licks indicating reduced conflict; NSF = reduced latency to feed; OF = increased % time in center; SI = increased
social interaction
Anticomplusive effects: MBT = reduced burying
Panicolytic effects: ETM = decreased escape; GABA
A
blockade in dlSC = defensive immobility, and explosive escape; PAG-E-Stim = increased threshold for escape; PS = reduced explosive escape
WR=Wistarrats;SM=Swissmice;L-EHR=Long–Evans hooded rats; i.p. = intraperitoneal; dlPAG = dorsolateral periaqueductal gray; i.c.v. = intracerebroventricular; PL = prelimbic; IL = infralimbic;
BNST = bed nucleus of the stria terminalis; CeA = amygdala central nucleus; SNpr = substantia nigra pars reticularis; CUS = chronic unpredictable stress; GSCT = Geller–Seifter conflict test; CER =
conditioned emotional response; EPM = elevated plus maze; VCT = Vogel conflict test; CFC = contextual fear conditioning; RS = restraint stress; ETM = elevated T maze; PAG E-stim = electrical
stimulation of the dlPAG; L-DT = light–dark test; SI = social interaction; OF = open field; MBT = marble-burying test; PS = predator stress; NSF = novelty suppressed feeding test; GABA
A
=γ-
aminobutyric acid receptor A; dlSC = deep layers superior colliculus; REM = rapid eye movement; NA = not applicable
Cannabidiol as a Potential Treatment for Anxiety Disorders
activation [79], and also upon microinjection into the cen-
tral nucleus of the amygdala [78]. In the prelimbic cortex,
which drives expression of fear responses via connections
with the amygdala [94], CBD had more complex effects: in
unstressed rats, CBD was anxiogenic in the EPM, partially
via 5-HT
1A
R receptor activation; however, following acute
restraint stress, CBD was anxiolytic [87]. Finally, the anxi-
olytic effects of systemic CBD partially depended on
GABA
A
receptor activation in the EPM model but not in
the VCT model [61,62].
As noted, CBD has been found to have a bell-shaped re-
sponse curve, with higher doses being ineffective. This may
reflect activation of TRPV1 receptors at higher dose, as block-
ade of TRPV1 receptors in the DPAG rendered a previously
ineffective high dose of CBD as anxiolytic in the EPM [66].
Given TRPV1 receptors have anxiogenic effects, this may
indicate that at higher doses, CBD’s interaction with TRPV1
receptors to some extent impedes anxiolytic actions,
although was notably not sufficient to produce anxiogenic
effects.
Stress-induced Anxiety Models
Stress is an important contributor to anxiety disorders, and
traumatic stress exposure is essential to the development of
PTSD. Systemically administered CBD reduced acute in-
creases in heart rate and blood pressure induced by restraint
stress, as well as the delayed (24 h) anxiogenic effects of stress
in the EPM, partially by 5-HT
1A
R activation [67,73]. How-
ever intra-BNST microinjection of CBD augmented stress-
induced heart rate increase, also partially via 5-HT
1A
Ractiva-
tion [85]. In a subchronic study, CBD administered daily 1 h
after predator stress (a proposed model of PTSD) reduced the
long-lasting anxiogenic effects of chronic predator stress, par-
tially via 5-HT
1A
R activation [77]. In a chronic study, system-
ic CBD prevented increased anxiety produced by chronic un-
predictable stress, in addition to increasing hippocampal
AEA; these anxiolytic effects depended upon CB
1
R activation
and hippocampal neurogenesis, as demonstrated by genetic
ablation techniques [81]. Prior stress also appears to modulate
CBD’s anxiogenic effects: microinjection of CBD into the
prelimbic cortex of unstressed animals was anxiogenic in the
EPM but following restraint stress was found to be anxiolytic
[87]. Likewise, systemic CBD was anxiolytic in the EPM
following but not prior to stress [65].
PD and Compulsive Behavior Models
CBD inhibited escape responses in the ETM and increased
DPAG escape electrical threshold [68], both proposed models
of panic attacks [95]. These effects partially depended on 5-
HT
1A
R activation but were not affected by CB
1
R blockade.
CBD was also panicolytic in the predator–prey model, which
assesses explosive escape and defensive immobility in re-
sponse to a boa constrictor snake, also partially via 5-HT
1A
R
activation; however, more consistent with an anxiogenic ef-
fect, CBD was also noted to decrease time spent outside the
burrow and increase defensive attention (not shown in
Table 1)[75,86] . Finally, CBD, partially via CB
1
Rs, de-
creased defensive immobility and explosive escape caused
by bicuculline-induced neuronal activation in the superior
colliculus [89]. Anticompulsive effects of CBD were investi-
gated in marble-burying behavior, conceptualized to model
OCD [96]. Acute systemic CBD reduced marble-burying be-
havior for up to 7 days, with no attenuation in effect up to high
(120 mg/kg) doses, and effect shown to depend on CB
1
Rs but
not 5-HT
1A
Rs [71,74,88].
Contextual Fear Conditioning, Fear Extinction,
and Reconsolidation Blockade
Several studies assessed CBD using contextual fear condition-
ing. Briefly, this paradigm involves pairing a neutral context,
the conditioned stimulus (CS), with an aversive unconditioned
stimulus (US), a mild foot shock. After repeated pairings, the
subject learns that the CS predicts the US, and subsequent CS
presentation elicits freezing and other physiological re-
sponses. Systemic administration of CBD prior to CS
re-exposure reduced conditioned cardiovascular re-
sponses [63], an effect reproduced by microinjection of
CBD into the BNST, and partially mediated by 5-
HT
1A
R activation [79]. Similarly, CBD in the prelimbic
cortex reduced conditioned freezing [70], an effect
preventedby5-HT
1A
Rblockade[87]. By contrast,
CBD microinjection in the infralimbic cortex enhanced
conditionedfreezing[70]. Finally, El Batsh et al. [80]
reported that repeated CBD doses over 21 days, that is
chronic as opposed to acute treatment, facilitated condi-
tioned freezing. In this study, CBD was administered
prior to conditioning rather than prior to re-exposure
as in acute studies, thus further directly comparable
studies are required.
CBD has also been shown to enhance extinction of
contextually conditioned fear responses. Extinction train-
ing involves repeated CS exposure in the absence of the
US, leading to the formation of a new memory that
inhibits fear responses and a decline in freezing over
subsequent training sessions. Systemic CBD administra-
tion immediately before training markedly enhanced ex-
tinction, and this effect depended on CB
1
R activation,
without involvement of TRPV1 receptors [65]. Further
studies showed CB
1
Rs in the infralimbic cortex may be
involved in this effect [82].
CBD also blocked reconsolidation of aversive memo-
ries in rat [76]. Briefly, fear memories, when reactivated
by re-exposure (retrieval), enter into a labile state in
Blessing et al.
which the memory trace may either be reconsolidated or
extinguished [97], and this process may be pharmacolog-
ically modulated to achieve reconsolidation blockade or
extinction. When administered immediately following re-
trieval, CBD prevented freezing to the conditioned con-
text upon further re-exposure, and no reinstatement or
spontaneous recovery was observed over 3 weeks, con-
sistent with reconsolidation blockade rather than extinc-
tion [76]. This effect depended on CB
1
R activation but
not 5-HT
1A
Ractivation[76].
Summary and Clinical Relevance
Overall, existing preclinical evidence strongly supports
the potential of CBD as a treatment for anxiety disor-
ders. CBD exhibits a broad range of actions, relevant to
multiple symptom domains, including anxiolytic,
panicolytic, and anticompulsive actions, as well as a
decrease in autonomic arousal, a decrease
in conditioned fear expression, enhancement of fear ex-
tinction, reconsolidation blockade, and prevention of the
long-term anxiogenic effects of stress. Activation of 5-
HT
1A
Rs appears to mediate anxiolytic and panicolytic
effects, in addition to reducing conditioned fear expres-
sion, although CB
1
R activation may play a limited role.
By contrast, CB
1
R activation appears to mediate CBD’s
anticompulsive effects, enhancement of fear extinction,
reconsolidation blockade, and capacity to prevent the
long-term anxiogenic consequences of stress, with in-
volvement of hippocampal neurogenesis.
While CBD predominantly has acute anxiolytic ef-
fects, some species discrepancies are apparent. In addi-
tion, effects may be contingent on prior stress and vary
according to brain region. A notable contrast between
CBD and other agents that target the eCB system, in-
cluding THC, direct CB
1
R agonists and FAAH inhibi-
tors, is a lack of anxiogenic effects at a higher dose.
Further receptor-specific studies may elucidate the recep-
tor specific basis of this distinct dose response profile.
Further studies are also required to establish the efficacy
of CBD when administered in chronic dosing, as rela-
tively few relevant studies exist, with mixed results, in-
cluding both anxiolytic and anxiogenic outcomes.
Overall, preclinical evidence supports systemic CBD
as an acute treatment of GAD, SAD, PD, OCD, and
PTSD, and suggests that CBD has the advantage of
not producing anxiogenic effects at higher dose, as dis-
tinct from other agents that enhance CB
1
R activation. In
particular, results show potential for the treatment of
multiple PTSD symptom domains, including reducing
arousal and avoidance, preventing the long-term adverse
effects of stress, as well as enhancing the extinction and
blocking the reconsolidation of persistent fear memories.
Human Experimental and Clinical Studies
Evidence from Acute Psychological Studies
Relevant studies are summarized in Table 2. The anxiolytic
effects of CBD in humans were first demonstrated in the con-
text of reversing the anxiogenic effects of THC. CBD reduced
THC-induced anxiety when administered simultaneously with
this agent, but had no effect on baseline anxiety when admin-
istered alone [99,100]. Further studies using higher doses
supported a lack of anxiolytic effects at baseline [101,107].
By contrast, CBD potently reduces experimentally induced
anxiety or fear. CBD reduced anxiety associated with a simu-
lated public speaking test in healthy subjects, and in subjects
with SAD, showing a comparable efficacy to ipsapirone (a 5-
HT
1A
Ragonist)ordiazepam[98,105]. CBD also reduced the
presumed anticipatory anxiety associated with undergoing a
single-photon emission computed tomography (SPECT) im-
aging procedure, in both healthy and SAD subjects [102,104].
Finally, CBD enhanced extinction of fear memories in healthy
volunteers: specifically, inhaled CBD administered prior to or
after extinction training in a contextual fear conditioning par-
adigm led to a trend-level enhancement in the reduction of
skin conductance response during reinstatement, and a signif-
icant reduction in expectancy (of shock) ratings during rein-
statement [106].
Evidence from Neuroimaging Studies
Relevant studies are summarized in Table 3. In a SPECT study
of resting cerebral blood flow (rCBF) in normal subjects,
CBD reduced rCBF in left medial temporal areas, including
the amygdala and hippocampus, as well as the hypothalamus
and left posterior cingulate gyrus, but increased rCBF in the
left parahippocampal gyrus. These rCBF changes were not
correlated with anxiolytic effects [102]. In a SPECT study,
by the same authors, in patients with SAD, CBD reduced
rCBF in overlapping, but distinct, limbic and paralimbic areas;
again, with no correlations to anxiolytic effects [104].
In a series of placebo-controlled studies involving 15
healthy volunteers, Fusar-Poli et al. investigated the effects
of CBD and THC on task-related blood-oxygen-level depen-
dent functional magnetic resonance imaging activation, spe-
cifically the go/no-go and fearful faces tasks [109,110]. The
go/no-go task measures response inhibition, and is associated
with activation of medial prefrontal, dorsolateral prefrontal,
and parietal areas [111]. Response activation is diminished
in PTSD and other anxiety disorders, and increased activation
predicts response to treatment [112]. CBD produced no
changes in predicted areas (relative to placebo) but reduced
activation in the left insula, superior temporal gyrus, and trans-
verse temporal gyrus. The fearful faces task activates the
amygdala, and other medial temporal areas involved in
Cannabidiol as a Potential Treatment for Anxiety Disorders
Tabl e 2 Human psychological studies
Study Subjects,
design
CBD route,
dose
Measure Effect
Karniol et al. [99]HV,
DBP
Oral, 15, 30, 60 mg, alone
or with THC,
acute, at 55, 95, 155, and
185 min
Anxiety and pulse rate after
THC and at baseline
↓THC-induced increases in
subjective anxiety and
pulse rate
No effect at
baseline
Zuardi et al., [100]HV,
DBP
Oral 1 mg/kg alone or with
THC, acute, 80 min
STAI score after THC ↓THC-induced increases in
STAI scores
Zuardi et al. [98]HV,
DBP
Oral 300 mg,
acute, 80 min
VAMS, STAI and BP
following SPST
↓STAI scores
↓VA M S s c o r e s
↓BP
Martin-Santos et al. [101]HV,
DBP
Oral 600 mg,
acute, 1, 2, 3 h
Baseline anxiety and
pulse rate
No effect
Crippa et al. [102]10HV,
DBP
Oral 400 mg,
acute, 60 and 75 min
VAMS before SPECT
SPECT
↓VA M S s c o r e s
Bhattacharyya et al. [103]15HV
DBP
Oral 600 mg,
acute, 1, 2, 3 h
STAI scores
VAMS scores
↓STAI scores
↓VA M S s c o r e s
Crippa et al. [104] SAD and HC
DBP
Oral 400 mg,
acute, 75 and 140 min
VAMS before SPECT
SPECT
↓VA M S s c o r e s
Bergamaschi et al. [105] SAD and HC DBP Oral 600 mg, acute,
1, 2, 3 h
VAMS, SSPS-N, cognitive
impairment, SCR, HR
after SPST
↓VAMS, SSPS-N and cognitive
impairment, no effect on SCR
or HR
Das et al. [106]HV
DBP
Inhaled, 32 mg, acute,
immediately following,
before, after extinction
SCR and shock expectancy
following extinction
CBD after extinction training
produced trend level reduction
inSCRanddecreasedshock
expectancy
Hindocha et al. [107] Varying in schizotypy and
cannabis use, DBP
Inhaled, 16 mg, acute Baseline VAS anxiety No significant effect of CBD
HV = healthy volunteers; DBP = double-blind placebo; SAD = social anxiety disorder; HC = healthy controls; THC =
Δ
9-tetrahydrocannabinol; STAI =
Spielberger’s state trait anxiety inventory; VAMS = visual analog mood scale; BP = blood pressure; SPST = simulated public speaking test; SCR = skin
conductance response; SPECT = single-photon emission computed tomography; SSPS-N = negative self-evaluation subscale; HR = heart rate; VAS =
visual analog scale, CBD = cannabidiol
Tabl e 3 Neuroimaging studies
Study Subjects, design CBD route, dose, timing Measure Effect of CBD
Crippa et al. [102]10HV,
DBP
Oral 400 mg,
acute, 60 and 75 min
SPECT, resting (rCBF) ↓rCBF in left medial temporal cluster,
including amygdala and HPC, also ↓rCBF
in the HYP and posterior cingulate gyrus
↑rCBF in left PHG
Borgwardt et al. [108]15HV,
DBP
Oral 600 mg,
acute, 1–2h
fMRI during oddball and
go/no-go task
↓Activation in left insula, STG and MTG
Fusar-Poli et al. [109]15HV,
DBP
Oral 600 mg,
acute, 1–2h
fMRI activation during
fearful faces task
↓Activation in left medial temporal region,
including amygdala and anterior PHG, and
in right ACC and PCC
Fusar-Poli et al. [110]15HV,
DBP
Oral 600 mg,
acute, 1–2h
fMRI functional connectivity
during fearful faces task
↓Functional connectivity between L) AMY
and ACC
Crippa et al. [104] SAD and HC
DBP
Oral 400 mg,
acute, 75 and 140 min
SPECT, resting (rCBF) ↓rCBF in the left PHG, HPC and ITG.
↑rCBF in the right posterior cingulate gyrus
CBD = cannabidiol; HV = healthy controls; DBP = double-blindplacebo; SAD= social anxiety disorder; HC = healthy controls; SPECT = single-photo
emission computed tomography; rCBF = regional cerebral blood flow; fMRI = functional magnetic resonance imaging; HPC = hippocampus; HYP =
hypothalamus; PHG = parahippocampal gyrus; STG = superior temporal gyrus; MTG = medial temporal gyrus; ACC = anterior cingulate cortex; PCC =
posterior cingulate cortex
Blessing et al.
emotion processing, and heightened amygdala response acti-
vation has been reported in anxiety disorders, including GAD
and PTSD [113,114]. CBD attenuated blood-oxygen-level
dependent activation in the left amygdala, and the anterior
and posterior cingulate cortex in response to intensely fearful
faces, and also reduced amplitude in skin conductance fluctu-
ation, which was highly correlated with amygdala activation
[109]. Dynamic causal modeling analysis in this data set fur-
ther showed CBD reduced forward functional connectivity
between the amygdala and anterior cingulate cortex [110].
Evidence from Epidemiological and Chronic Studies
Epidemiological studies of various neuropsychiatric disorders
indicate that a higher CBD content in chronically consumed
cannabis may protect against adverse effects of THC, includ-
ing psychotic symptoms, drug cravings, memory loss, and
hippocampal gray matter loss [115–118] (reviewed in [119]).
As THC acutely induces anxiety, this pattern may also be
evident for chronic anxiety symptoms. Two studies were iden-
tified, including an uncontrolled retrospective study in civilian
patients with PTSD patients [120], and a case study in a pa-
tient with severe sexual abuse-related PTSD [121], which
showed that chronic cannabis use significantly reduces PTSD
symptoms; however, these studies did not include data on the
THC:CBD ratio. Thus, overall, no outcome data are currently
available regarding the chronic effects of CBD in the treat-
ment of anxiety symptoms, nor do any data exist regarding the
potential protective effects of CBD on anxiety potentially in-
duced by chronic THC use.
Summary and Clinical Relevance
Evidence from human studies strongly supports the potential
for CBD as a treatment for anxiety disorders: at oral doses
ranging from 300 to 600 mg, CBD reduces experimentally
induced anxiety in healthy controls, without affecting baseline
anxiety levels, and reduces anxiety in patients with SAD.
Limited results in healthy subjects also support the efficacy
of CBD in acutely enhancing fear extinction, suggesting po-
tential for the treatment of PTSD, or for enhancing cognitive
behavioral therapy. Neuroimaging findings provide evidence
of neurobiological targets that may underlie CBD’s anxiolytic
effects, including reduced amygdala activation and altered
medial prefrontal amygdala connectivity, although current
findings are limited by small sample sizes, and a lack of inde-
pendent replication. Further studies are also required to estab-
lish whether chronic, in addition to acute CBD dosing is an-
xiolytic in human. Also, clinical findings are currently limited
to SAD, whereas preclinical evidence suggests CBD’spoten-
tial to treat multiple symptom domains relevant to GAD, PD,
and, particularly, PTSD.
Conclusions
Preclinical evidence conclusively demonstrates CBD’seffica-
cy in reducing anxiety behaviors relevant to multiple disor-
ders, including PTSD, GAD, PD, OCD, and SAD, with a
notable lack of anxiogenic effects. CBD’s anxiolytic actions
appear to depend upon CB
1
Rs and 5-HT
1A
Rs in several brain
regions; however, investigation of additional receptor actions
may reveal further mechanisms. Human experimental find-
ings support preclinical findings, and also suggest a lack of
anxiogenic effects, minimal sedative effects, and an excellent
safety profile. Current preclinical and human findings mostly
involve acute CBD dosing in healthy subjects, so further stud-
ies are required to establish whether chronic dosing of CBD
has similar effects in relevant clinical populations. Overall,
this review emphasizes the potential value and needfor further
study of CBD in the treatment of anxiety disorders.
Required Author Forms Disclosure forms provided by the authors are
available with the online version of this article.
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