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Cannabis and Cannabis Extracts:
Greater Than the Sum of Their Parts?
John M. McPartland
Ethan B. Russo
SUMMARY. A central tenet underlying the use of botanical remedies is
that herbs contain many active ingredients. Primary active ingredients
may be enhanced by secondary compounds, which act in beneficial syn-
ergy. Other herbal constituents may mitigate the side effects of dominant
active ingredients. We reviewed the literature concerning medical can-
nabis and its primary active ingredient, ∆9-tetrahydrocannabinol (THC).
Good evidence shows that secondary compounds in cannabis may enhance
the beneficial effects of THC. Other cannabinoid and non-cannabinoid
compounds in herbal cannabis or its extracts may reduce THC-induced
anxiety, cholinergic deficits, and immunosuppression. Cannabis terpenoids
and flavonoids may also increase cerebral blood flow, enhance cortical
activity, kill respiratory pathogens, and provide anti-inflammatory activ-
ity. [Article copies available for a fee from The Haworth Document Delivery
Service: 1-800-342-9678. E-mail address: <getinfo@haworthpressinc.com>
Website: <http://www.HaworthPress.com> 2001 by The Haworth Press, Inc.
All rights reserved.]
John M. McPartland, DO, MS, is affiliated with GW Pharmaceuticals, Ltd., Porton
Down Science Park, Salisbury, Wiltshire, SP4 0JQ, UK.
Ethan B. Russo, MD, is affiliated with Montana Neurobehavioral Specialists, 900
North Orange Street, Missoula, MT 59802 USA.
Address correspondence to: John M. McPartland, DO, Faculty of Health & Environ-
mental Science, UNITEC, Private Bag 92025, Auckland, New Zealand (E-mail: jmcpartland
@unitec.ac.nz).
The authors thank David Pate and Vincenzo Di Marzo for pre-submission reviews.
[Haworth co-indexing entry note]: “Cannabis and Cannabis Extracts: Greater Than the Sum of Their
Parts?” McPartland, John M., and Ethan B. Russo. Co-published simultaneously in Journal of Cannabis Ther-
apeutics (The Haworth Integrative Healing Press, an imprint of The Haworth Press, Inc.) Vol. 1, No. 3/4,
2001, pp. 103-132; and: Cannabis Therapeutics in HIV/AIDS (ed: Ethan Russo) The Haworth Integrative
Healing Press, an imprint of The Haworth Press, Inc., 2001, pp. 103-132. Single or multiple copies of this arti-
cle are available for a fee from The Haworth Document Delivery Service [1-800-342-9678, 9:00 a.m. - 5:00
p.m. (EST). E-mail address: getinfo@haworthpressinc.com].
2001 by The Haworth Press, Inc. All rights reserved. 103
KEYWORDS. Cannabis, marijuana, THC, cannabinoids, phytocanna-
binoids, cannabidiol, cannabichromene, cannabibigerol, tetrahydrocanna-
bivarin, terpenoids, essential oils, flavonoids, herbal medicine, medicinal
plants, herbal synergy
INTRODUCTION
Cannabis is an herb; it contains hundreds of pharmaceutical compounds
(Turner et al. 1980). Herbalists contend that polypharmaceutical herbs provide
two advantages over single-ingredient synthetic drugs: (1) therapeutic effects
of the primary active ingredients in herbs may be synergized by other com-
pounds, and (2) side effects of the primary active ingredients may be mitigated
by other compounds. Thus, cannabis has been characterized as a “synergistic
shotgun,” in contrast to Marinol(∆9-tetrahydrocannabinol, THC), a syn-
thetic, single-ingredient “silver bullet” (McPartland and Pruitt 1999).
Mechoulam et al. (1972) suggested that other compounds present in herbal
cannabis might influence THC activity. Carlini et al. (1974) determined that
cannabis extracts produced effects “two or four times greater than that ex-
pected from their THC content.” Similarly, Fairbairn and Pickens (1981) de-
tected the presence of unidentified “powerful synergists” in cannabis extracts
causing 330% greater activity in mice than THC alone.
Other compounds in herbal cannabis may ameliorate the side effects of
THC. Whole cannabis causes fewer psychological side effects than synthetic
THC, seen as symptoms of dysphoria, depersonalization, anxiety, panic reac-
tions, and paranoia (Grinspoon and Bakalar 1997). This difference in side ef-
fect profiles may also be due, in part, to differences in administration: THC
taken by mouth undergoes “first pass metabolism” in the small intestine and
liver, to 11-hydroxy THC; the metabolite is more psychoactive than THC itself
(Browne and Weissman 1981). Inhaled THC undergoes little first-pass metab-
olism, so less 11-hydroxy THC is formed. Thus, “smoking cannabis is a satis-
factory expedient in combating fatigue, headache and exhaustion, whereas the
oral ingestion of cannabis results chiefly in a narcotic effect which may cause
serious alarm” (Walton 1938, p. 49).
Respiratory side effects from inhaling cannabis smoke may be ameliorated by
both cannabinoid and non-cannabinoid components in cannabis. For instance,
throat irritation may be diminished by anti-inflammatory agents, mutagens in
the smoke may be mitigated by antimutagens, and bacterial contaminants in
cannabis may be annulled by antibiotic compounds (McPartland and Pruitt
1997). The pharmaceutically active compounds in cannabis that enhance ben-
eficial THC activity and reduce side effects are relatively unknown. The pur-
104 CANNABIS THERAPEUTICS IN HIV/AIDS
pose of this paper is to review the biochemistry and physiological effects of
those other compounds.
MATERIALS AND METHODS
MEDLINE (1966-2000) was searched using MeSH keywords: cannabin-
oids, marijuana, tetrahydrocannabinol. AGRICOLA (1990-1999) was searched
using the keywords cannabis, hemp, and marijuana. Phytochemical and ethno-
botanical databases were searched via the Agricultural Research Service
webpage <http://www.ars-grin.gov/~ngrlsb/>. All reports were scanned for
supporting bibliographic citations; antecedent sources were retrieved to the
fullest possible extent. Data validity was assessed by source (peer-reviewed
article vs. popular press), identification methodology (analytical chemistry vs.
clinical history) and the frequency of independent observations.
RESULTS AND DISCUSSION
Turner et al. (1980) listed over 420 compounds in cannabis. Sparacino et al.
(1990) listed 200 additional compounds in cannabis smoke. We will highlight
six cannabinoids beyond THC, a dozen-odd terpenoids, three flavonoids, and
one phytosterol. Other non-cannabinoids with proven pharmacological activ-
ity include poorly characterized glycoproteins, alkaloids, and compounds that
remain completely unidentified (Gill et al. 1970).
CANNABINOIDS
Mechoulam and Gaoni (1967) defined “cannabinoids” as a group of C21
terpenophenolic compounds uniquely produced by cannabis. The subsequent
development of synthetic cannabinoids (e.g., HU-210) has blurred this defini-
tion, as has the discovery of endogenous cannabinoids (e.g., anandamide), de-
fined as “endocannabinoids” by DiMarzo and Fontana (1995). Thus, Pate
(1999) proposed the term “phytocannabinoids” to designate the C21 com-
pounds produced by cannabis. Phytocannabinoids exhibit very low mamma-
lian toxicity, and mixtures of cannabinoids are less toxic than pure THC
(Thompson et al. 1973).
Cannabidiol (CBD) is the next-best studied phytocannabinoid after THC
(Figure 1). The investigation of CBD by marijuana researchers is rather para-
doxical, considering its concentrations are notably lower in drug varieties of
cannabis than in fiber cultivars (Turner et al. 1980).
John M. McPartland and Ethan B. Russo 105
CBD possesses sedative properties (Carlini and Cunha, 1981), and a clini-
cal trial showed that it reduces the anxiety and other unpleasant psychological
side effects provoked by pure THC (Zuardi et al. 1982). CBD modulates the
pharmacokinetics of THC by three mechanisms: (1) it has a slight affinity for
cannabinoid receptors (Ki at CB1 = 4350 nM, compared to THC = 41 nM,
Showalter et al. 1996), and it signals receptors as an antagonist or reverse ago-
nist (Petitet et al. 1998), (2) CBD may modulate signal transduction by per-
turbing the fluidity of neuronal membranes, or by remodeling G-proteins that
carry intracellular signals downstream from cannabinoid receptors, and (3) CBD
is a potent inhibitor of cytochrome P450 3A11 metabolism, thus it blocks the
hydroxylation of THC to its 11-hydroxy metabolite (Bornheim et al. 1995).
The 11-hydroxy metabolite is four times more psychoactive than unmetabo-
lized THC (Browne and Weissman 1981), and four times more immuno-
suppressive (Klein et al. 1987).
CBD provides antipsychotic benefits (Zuardi et al. 1995). It increases dopa-
mine activity, serves as a serotonin uptake inhibitor, and enhances norepin-
ephrine activity (Banerjee et al. 1975; Poddar and Dewey 1980). CBD protects
neurons from glutamate toxicity and serves as an antioxidant, more potently
than ascorbate and α-tocopherol (Hampson et al. 1998). Auspiciously, CBD
does not decrease acetylcholine (ACh) activity in the brain (Domino 1976;
Cheney et al. 1981). THC, in contrast, reduces hippocampal ACh release in
rats (Carta et al. 1998), and this correlates with loss of short-term memory con-
solidation. In the hippocampus THC also inhibits N-methyl-D-aspartate (NMDA)
receptor activity (Misner and Sullivan 1999; Shen and Thayer 1999), and
NMDA synaptic transmission is crucial for memory consolidation (Shimizu et
al. 2000). CBD, unlike THC, does not dampen the firing of hippocampal cells
(Heyser et al. 1993) and does not disrupt learning (Brodkin and Moersch-
baecher 1997).
Consroe (1998) presented an excellent review of CBD in neurological dis-
orders. In some studies, it ameliorates symptoms of Huntington’s disease, such
as dystonia and dyskinesia. CBD mitigates other dystonic conditions, such as
torticollis, in rat studies and uncontrolled human studies. CBD functions as an
anticonvulsant in rats, on a par with phenytoin (Dilantin, a standard anti-
epileptic drug).
CBD demonstrated a synergistic benefit in the reduction of intestinal motil-
ity in mice produced by THC (Anderson, Jackson, and Chesher 1974). This
may be an important component of observed benefits of cannabis in inflamma-
tory bowel diseases.
The CBD in cannabis smoke may explain why inhaling it causes less airway
irritation and inflammation than inhalation of pure THC (Tashkin et al. 1977).
CBD imparts analgesia (more potently than THC), it inhibits erythema (much
more than THC), it blocks cyclooxygenase (COX) activity with a greater max-
106 CANNABIS THERAPEUTICS IN HIV/AIDS
imum inhibition than THC, and it blocks lipoxygenase (the enzyme that pro-
duces asthma-provoking leukotrienes), again more effectively than THC (Evans
1991). Mice with inflammatory collagen-induced arthritis (a mouse model for
rheumatoid arthritis) were given oral CBD (5 mg/kg per day) and showed clin-
ical improvement, and the treatment effectively blocked progression of the ar-
thritis (Malfait et al. 2000).
CBD reportedly has little or no effect on the immune system (reviewed by
Klein et al. 1998), although the mouse arthritis study by Malfait et al. (2000)
showed CBD decreases the production of tumor necrosis factor (TNF) and In-
terferon-gamma (IFN-γ), which are two immunomodulatory cytokines de-
scribed later. CBD actually kills bacteria and fungi, with greater potency than
THC (Klingeren and Ham 1976; ElSohly et al. 1982; McPartland 1984). Thus,
cannabis may have less microbial contamination than other herbs, an impor-
tant consideration for immunocompromised individuals (McPartland and Pruitt
1997).
Cannabinol (CBN) is the degradation product of THC (Turner et al. 1980),
and is found most often in aged cannabis products (Figure 1). CBN potentiates
the effects of THC in man (Musty et al. 1976), yet it antagonizes the effects of
THC in mice (Formukong et al. 1988). Studies reporting CBN’s effects upon
norepinephrine and dopamine also conflict–CBN may have negligible effects
on these biogenic amines (Banerjee et al. 1975), enhance their release (Poddar
and Dewey 1980), or decrease their release (Dalterio et al. 1985). CBN in-
creases plasma concentrations of follicle-stimulating hormone, and enhances
the production of testicular testosterone (Dalterio et al. 1985). CBN shares
some characteristics with CBD; for example, it has anti-convulsant activity
(Turner et al. 1980) and anti-inflammatory activity (Evans et al. 1991).
CBN has affinity for CB1receptors (Ki at CB1 = 308 nM) and signals as an
agonist (Showalter et al. 1996). Further down the signal transduction cascade,
it stimulates the binding of GTP-γ-S (Petitet et al. 1998), but with half the effi-
cacy of THC; when CBN is added to THC, the effects are not significantly ad-
ditive. CBN has a three-fold greater affinity for CB2receptors (Ki = 96 nM)
(Showalter et al. 1996), thus it may affect cells of the immune system more
than the central nervous system (Klein et al. 1998). CBN modulates thymocytes
(Herring and Kaminski 1999) by attenuating the activity of the c-AMP re-
sponse element-binding protein (CREB), nuclear factor κB (NF-κB), and
interleukin-2 (IL-2). IL-2 is regulated by activator protein-1 (AP-1) transcrip-
tion factor, a complex of c-Fos and c-Jun proteins (Foletta et al. 1998); CBN
inhibits the expression of these proteins in splenocytes, via decreased activa-
tion of ERK MAP kinases (Faubert and Kaminski 2000).
Cannabichromene (CBC) is the fourth major cannabinoid, found predomi-
nantly in tropical Cannabis spp. strains (Figure 1). Until the mid-1970s, CBC
was frequently misidentified as CBD, because CBC and CBD have nearly the
John M. McPartland and Ethan B. Russo 107
same retention times in gas chromatography. Like CBD, CBC decreases in-
flammation (Wirth et al. 1980) and provides analgesic effects (Davis and
Hatoum 1983). CBC inhibits prostaglandin synthesis in vitro, but less potently
than CBD or THC (Burstein et al. 1973). CBC exhibits strong antibacterial ac-
tivity and mild antifungal activity, superior to THC and CBD in most instances
(ElSohly et al. 1982). Unlike CBD, CBC has no effect on cytochrome P450 en-
zymes (Kapeghian et al. 1983), nor does it function as an anticonvulsant in rats
(Davis and Hatoum 1983).
The molecular affinity of CBC for cannabinoid receptors has not been mea-
sured. In mice, CBC causes hypothermia, sedation, and synergizes the depres-
sant effects of hexobarbital (Hatoum et al. 1981). CBC also sedates dogs and
decreases muscular coordination in rats, but causes no cannabimimetic activ-
ity in monkeys and people (Turner et al. 1980). In rats, the co-administration of
CBC with THC potentiates THC changes in heart rate, but does not potentiate
THC’s hypotensive effects (O’Neil et al. 1979). Co-administration of CBC
lowers the LD50 dose of THC in mice (Hatoum et al. 1981).
Cannabigerol (CBG) is the biosynthetic precursor of CBC, CBD, and THC,
and is present only in minor amounts (Figure 1). CBG has been called “inac-
tive” when compared to THC, but CBG has slight affinity for CB1receptors,
approximately the same as CBD (Devane et al. 1988). In rat brains, CBG in-
hibits the uptake of serotonin and norepinephrine, less effectively than CBD
and THC, but CBG inhibits GABA uptake more effectively than CBD and THC
(Banerjee et al. 1975). CBG acts as an analgesic (more potently than THC), it
inhibits erythema (much more than THC), and it blocks lipoxygenase, again
more effectively than THC (reviewed by Evans 1991).
CBG has antibacterial properties (Mechoulam and Gaoni 1965). Its activity
against gram-positive bacteria, mycobacteria, and fungi is superior to that of
THC, CBD, and CBC (ElSohly et al. 1982). CBG inhibits the growth of human
oral epitheloid carcinoma cells (Baek et al. 1998).
Delta-8-THC (∆8-THC) is an isomer of delta-9-THC; it differs only by the
location of the double bond in the cyclohexal “C” ring. The Ki of ∆8-THC is
126 nM (Compton et al. 1993), and this loosely correlates with human studies,
which show ∆8-THC is less psychoactive than ∆9-THC (Hollister 1974). The
chemical stability of ∆8-THC and its relative ease of synthesis compared to
∆9-THC, have made ∆8-THC the template for the development of two impor-
tant synthetic derivatives, the extremely potent psychoactive CB1agonist,
HU-210 (Mechoulam and Ben-Shabat 1999), and the non-psychoactive anti-
emetic and neuroprotectant, HU-211 (dexanabinol) (Achiron et al. 2000;
Biegon and Joseph 1995; Gallily et al. 1997). ∆8-THC was employed clini-
cally in an important study (Abrahamov and Mechoulam 1995) in which 8
children with hematological malignancies were treated with the drug over the
course of 8 months at a dose of 18 mg/m2to treat chemotherapy-associated
108 CANNABIS THERAPEUTICS IN HIV/AIDS
nausea and vomiting. Interestingly, not only was this agent uniformly effective
as an antiemetic, but it was also free of psychoactive effects in this age range
(2-13 years).
Tetrahydrocannabivarin (THCV) is a propyl analogue of ∆9-THC, primar-
ily appearing in indica and afghanica varieties of cannabis, such as hashish
from Nepal (Merkus 1971), dagga from South Africa (Boucher et al. 1977),
and in plants cultivated from seeds from Zambia (Pitts et al. 1992) (Figure 1).
THCV is only 20-25% as psychoactive as ∆9-THC (Hollister 1974). It has a
quicker onset of action than ∆9-THC (Gill et al. 1970), and is of briefer dura-
tion (Clarke 1998). THCV may be clinically effective in migraine treatment
(Personal communication, HortaPharm, November 2000). Kubena and Barry
(1972) suggested THCV synergizes the effects of THC, but did not hypothe-
size a mechanism. As a legal fine point, this analogue is not controlled in the
Netherlands, and is not specified in the USA as a Schedule I drug, but would
likely be considered illegal under the Controlled Substance Analogue Enforce-
ment Act of 1986 (Public Law 99-570). THCV is of interest from a medical-le-
gal standpoint in that is has been suggested as a biochemical marker of illicit
cannabis use, since it is not a metabolite of Marinol(synthetic THC) (ElSohly
et al. 1999).
TERPENOIDS
The unique smell of cannabis does not arise from cannabinoids, but from
over 100 terpenoid compounds (Turner et al. 1980). Terpenoids derive from
repeating units of isoprene (C5H8), such as monoterpenoids (with C10 skele-
tons), sesquiterpenoids (C15), diterpenoids (C20), and triterpenoids (C30). The
final structure of terpenoids ranges from simple linear chains to complex
polycyclic molecules, and they may include alcohol, ether, aldehyde, ketone,
or ester functional groups. These compounds are easily extracted from plant
material by steam distillation or vaporization. This distillate is called the es-
sential oil or volatile oil of the plant. A range of researchers cite different
yields of essential oil from different types of cannabis: Martin et al. (1961)
cited yields of 0.05-0.11% essential oil from fresh, green leaves and flowers of
mixed male and female plants, from feral hemp growing in Canada. Nigram et
al. (1965) yielded 0.1% essential oil from fresh, whole, male plants from Kash-
mir. Malingré et al. (1973) yielded 0.12% essential oil from fresh leaves of
“strain X” obtained from birdseed in the Netherlands. Ross and ElSohly
(1996) yielded 0.29% essential oil from fresh marijuana buds, reputed to be the
Afghani variety “Skunk #1.” Drying the plant material led to a loss of water
content and net weight, concentrating the essential oil to 0.80% in buds that
had been dried at room temperature for one week (Ross and ElSohly 1966).
John M. McPartland and Ethan B. Russo 109
Field-cultivated cannabis yields about 1.3 liter of essential oil per metric ton
of freshly harvested plant material (Mediavilla and Steinemann 1997). Pre-
venting pollination increases the yield of essential oil–18 l/ha in sinsemilla
crops, versus 8 l/ha in pollinated crops (Meier and Mediavilla 1998). The com-
position of terpenoids varies between strains of cannabis (Mediavilla and
Steinemann 1997), and varies between harvest dates (Meier and Mediavilla
1998).
Many terpenoids vaporize near the same temperature as THC, which boils
at 157°C (see Figures 1-2). Terpenoids are lipophilic and permeate lipid mem-
branes. Many cross the blood-brain barrier (BBB) after inhalation (Buchbauer
et al. 1993; Nasel et al. 1994).
Meschler and Howlett (1999) discussed several mechanisms by which
terpenoids modulate THC activity. For instance, terpenoids may bind to
cannabinoid receptors. Thujone, from Artemisia absinthium, has a weak affin-
ity for CB1receptors (Ki at CB1= 130,000 nM). Terpenoids might modulate
the affinity of THC for its own receptor, by sequestering THC, by perturbing
annular lipids surrounding the receptor, or by increasing the fluidity of neuronal
membranes. Further downstream, terpenoids may alter the signal cascade by
remodeling G-proteins. Terpenoids may alter the pharmacokinetics of THC by
changing the BBB; cannabis extracts are known to cause a significant increase
in BBB permeability (Agrawal et al. 1989). Terpenoids may also act on other
receptors and neurotransmitters. Some terpenoids act as serotonin uptake in-
hibitors (as does Prozac), enhance norepinephrine activity (as do tricyclic
antidepressants), increase dopamine activity (as do monoamine oxidase inhib-
itors and bupropion), and augment GABA (as do baclofen and the benzodiaz-
epines). Recently, strong serotonin activity at the 5-HT1A and 5-HT2a receptors
has been demonstrated (Russo et al. 2000; Russo 2001) that may support syn-
ergistic contributions of terpenoids on cannabis-mediated pain and mood ef-
fects. Further studies are in progress to identify the most active terpenoid
components responsible, and whether synergism of the components is demon-
strable.
The essential oil of cannabis is traditionally employed as an anti-inflamma-
tory in the respiratory and digestive tracts without known contraindications at
physiological dosages (Franchomme and Pénoël 1990). The essential oil of
black pepper, Piper nigrum, has a composition of terpenes that is qualitatively
quite similar to that of cannabis (Lawless 1995). It has often been claimed
anecdotally, that smoked cannabis may substitute for nicotine in attempts at
smoking cessation. Aside from cannabinoid influences, current evidence sup-
ports this contention based on terpene content and its activity. A recent study
has shown that inhalation of black pepper essential oil vapor significantly re-
duced withdrawal symptoms and anxiety in tobacco smokers (Rose and Behm
1994). Interestingly, the authors posited not a central biochemical mechanism,
110 CANNABIS THERAPEUTICS IN HIV/AIDS
John M. McPartland and Ethan B. Russo 111
FIGURE 1. Phytocannabinoids
Structure* Concentration†
(% dry weight) Boiling
Point °C§Properties
∆-9-tetrahydrocannabinol (THC) 0.1-25% 157 Euphoriant
Analgesic
Antiinflammatory
Antioxidant
Antiemetic
cannabidiol (CBD) 0.1-2.89% 160-180 Anxiolytic
Analgesic
Antipsychotic
Antiinflammatory
Antioxidant
Antispasmodic
cannabinol (CBN) 0.0-1.6% 185 Oxidation
breakdown
product
Sedative
Antibiotic
cannabichromene (CBC) 0.0-0.65% 220 Antiinflammatory
Antibiotic
Antifungal
cannabigerol (CBG) 0.03-1.15% MP
52 Antiinflammatory
Antibiotic
Antifungal
O
CH3
CH3
OH
H3C
OH
CH3
OH
CH3
CH2
O
CH3
CH3
CH3
OH
O
OH
HO
OH
but rather a peripheral one assuming physical cues of bronchial sensation as
operative in the origin of the benefit. The true scope of the essential oil benefits
in this context may be quite a bit broader.
Pate (1994), McPartland (1997), and McPartland, Clarke and Watson
(2000), have reviewed the pesticidal properties of cannabis attributable to its
terpenoid content. The essential oil of Eugenia dysenterica was recently dem-
onstrated to have significant inhibitory effects on Cryptococcus neoformans
strains isolated from HIV patients with cryptococcal meningitis (Costa et al.
2000). Key components of that oil were common to cannabis: β-caryo-
phyllene, α-humulene, α-terpineol, and limonene.
Additionally, monoterpenes such as those abundant in cannabis resin have
been suggested to: (1) inhibit cholesterol synthesis, (2) promote hepatic en-
112 CANNABIS THERAPEUTICS IN HIV/AIDS
FIGURE 1 (continued)
Structure* Concentration†
(% dry weight) Boiling
Point °C§Properties
∆-8-tetrahydrocannabinol (∆-8-THC) 0.0-0.1% 175-178 Resembles
∆-9-THC
Less psychoactive
More stable
Antiemetic
tetrahydrocannabivarin (THCV) 0.0-1.36% < 220 Analgesic
Euphoriant
*Structures of constituents obtained from Bissett and Wichtl 1994; British Medical Association 1997; Buckingham
1992; Iversen 2000; Tisserand and Balacs 1995; Turner et al. 1980.
†Concentrations of constituents (v/w or w/w) were calculated from various sources. Cannabinoid concentrations
(presented as a range, including cannabinoids and cannabinoidic acids) were primarily obtained from Small, 1979;
Veszki et al., 1980; Fournier et al., 1987; and Pitts et al., 1992. Terpenoid data (presented as maximum values)
were calculated from Ross and El Sohly, 1996; and Mediavilla and Steinemann, 1997. Flavonoid data came from
Paris et al., 1976; and Barrett et al., 1986.
§Boiling/meltingpoints(MP)recordedatatmosphericpressure(760mmHg)unlessotherisenoted;valuesobtained
from various sources, primarily Buckingham, 1992; Guenther, 1948; Parry, 1918; and Mechoulam (personal com-
munication, April 2001).
O
CH3
CH3
OH
H3C
O
OH
John M. McPartland and Ethan B. Russo 113
FIGURE 2. Terpenoid essential oil components of cannabis.
Cannabis Constituent Structure* Concentration†Boiling
Point °C§Properties
β-myrcene 0.47% 166-168 Analgesic
Antiinflammatory
Antibiotic
Antimutagenic
β-caryophyllene 0.05% 119 Antiinflammatory
Cytoprotective
(gastric mucosa)
Antimalarial
d-limonene 0.14% 177 Cannabinoid agonist?
Immune potentiator
Antidepressant
Antimutagenic
linalool 0.002% 198 Sedative
Antidepressant
Anxiolytic
Immune potentiator
pulegone 0.001% 224 Memory booster?
AChE inhibitor
Sedative
Antipyretic
1,8-cineole (eucalyptol) > 0.001% 176 AChE inhibitor
Increases cerebral
blood flow
Stimulant
Antibiotic
Antiviral
Antiinflammatory
Antinociceptive
α-pinene 0.04% 156 Antiinflammatory
Bronchodilator
Stimulant
Antibiotic
Antineoplastic
AChE inhibitor
H
HO
O
O
zyme activity to detoxify carcinogens, (3) stimulate apoptosis in cells with
damaged DNA, and (4) inhibit protein isoprenylation implicated in malignant
deterioration (Jones 1999).
Myrcene, specifically β-myrcene, a noncyclic monoterpene, is the most
abundant terpenoid produced by cannabis (Ross and ElSohly 1996; Mediavilla
and Steinemann 1997). It also occurs in high concentrations in hops (Humulus
lupulus) and lemongrass (Cymbopogon citratus). Myrcene is a potent analge-
sic, acting at central sites that are antagonized by naloxone (Rao et al. 1990).
Myrcene also works via a peripheral mechanism shared by CBD, CBG, and
CBC–by blocking the inflammatory activity of prostaglandin E2(Lorenzetti et
al. 1991). This activity is expressed by other terpenoids in cannabis smoke,
114 CANNABIS THERAPEUTICS IN HIV/AIDS
FIGURE 2 (continued)
Cannabis Constituent Structure* Concentration†Boiling
Point °C§Properties
α-terpineol 0.02% 217-218 Sedative
Antibiotic
AChE inhibitor
Antioxidant
Antimalarial
terpineol-4-ol 0.0004% 209 AChE inhibitor
Antibiotic
p
-cymene 0.0004% 177 Antibiotic
Anticandidal
AChE inhibitor
borneol 0.008% 210 Antibiotic
∆-3-carene 0.004% 168 Antiinflammatory
OH
OH
OH
such as carvacrol, which is more potent than THC or CBG (Burstein et al.
1975). The activity of many terpenoids may be cumulative: unfractionated
cannabis essential oil exhibits greater antiinflammatory activity than its indi-
vidual constituents, suggesting synergy (Evans et al. 1987).
Myrcene also synergizes the antibiotic potency of other essential oil com-
ponents, against Staphylococcus aureus, Bacillus subtilis, Pseudomonas aeru-
ginosa, and a specific strain of Escherichia coli (Onawunmi et al. 1984).
Myrcene inhibits cytochrome P450 2B1, an enzyme implicated in the meta-
bolic activation of promutagens (De Oliveira et al. 1997). Aflatoxin B1is a
promutagen produced by Aspergillus flavus and Aspergillus parasiticus, two
fungal contaminants of moldy marijuana (reviewed by McPartland and Pruitt
1997). After aflatoxin B1is metabolized by P450 2B1, it becomes extremely
hepatocarcinogenic. Myrcene blocks this metabolism, as do other terpenoids
in cannabis, including limonene, α-pinene, α-terpinene, and citronellal (De
Oliveira et al. 1997).
β-Caryophyllene is the most common sesquiterpenoid in cannabis (Mediavilla
and Steinemann 1997). It is the main component of copaiba balsam, from
Copaifera spp. (Lawless 1995), which is a popular oral and topical anti-in-
flammatory agent in Brazil (Basile et al. 1988). The latter authors were able to
demonstrate anti-inflammatory effects of the oleoresin in rats comparable to
phenylbutazone, in reduction of granuloma formation. A decreased vascular
permeability to injected histamine was also observed.
A gastric cytoprotective effect of β-caryophyllene was demonstrated in rats
against challenge with absolute ethanol and hydrochloric acid (Tambe et al.
1996). This benefit was noted without influence on gastric acid or pepsin se-
cretion. The authors suggested this agent as clinically safe, and potentially use-
ful. Campbell et al. (1997) have demonstrated a moderate antimalarial effect
against two strains of Plasmodium falciparum by an essential oil rich in
β-caryophyllene and α-terpineol.
Limonene is a monocyclic monoterpenoid and a major constituent of citrus
rinds (Tisserand and Balacs 1995). It finds extensive use as a solvent and in the
perfumery and flavor industries. Because of limonene’s widespread occur-
rence and application, its biological activity is well known. Limonene is highly
absorbed by inhalation and quickly appears in the bloodstream (Falk-Flilips-
son et al. 1993). According to Ross and ElSohly (1996), limonene is the second
most common terpenoid in an unidentified cultivar of cannabis.
Limonene may have a low-affinity interaction with cannabinoid receptors
(Meschler and Howlett 1999). Studies of long-term inhalation of lemon fra-
grance (predominately limonene) have demonstrated inhibition of thymic in-
volution in stress-induced immunosuppression in mice (Ortiz de Urbina et al.
1989).
John M. McPartland and Ethan B. Russo 115
Limonene was the primary component of the essential oil mixture em-
ployed by Komori et al. (1995), in their clinical study of immune function and
depressive states in humans. The key result of this experiment was the ability
to markedly reduce the dosage of, or even eliminate the need for, synthetic an-
tidepressant drugs.
As mentioned in the myrcene section, limonene protects against aflatoxin
B1-induced cancer by inhibiting the hepatic metabolism of the promutagen to
its active form. Limonene also blocks this process at two earlier steps by inhibit-
ing the growth of Aspergillus fungi and inhibiting their production of aflatoxins
(Greene-McDowelle et al. 1999). Limonene and other terpenoids suppress the
growth of many species of fungi and bacteria, demonstrated in hundreds of
published studies (reviewed by McPartland 1997).
Limonene blocks the carcinogenesis induced by benz[α]anthracene (Crowell
1999), a component of the “tar” generated by the combustion of herbal canna-
bis. Thus, this terpenoid may reduce the harm caused by inhaling cannabis
smoke. Limonene blocks carcinogenesis by multiple mechanisms. It detoxi-
fies carcinogens by inducing Phase II carcinogen-metabolizing enzymes (Crowell
1999). It selectively inhibits the isoprenylation of Ras proteins, thus blocking
the action of mutant ras oncogenes (Hardcastle et al. 1999). It induces re-
differentiation of cancer cells (by enhancing expression of transforming growth
factor β1 and growth factor II receptors), and it induces apoptosis of cancer
cells (Crowell 1999). Orally administered limonene is currently undergoing
Phase II clinical trials in the treatment of breast cancer (Vigushin et al. 1998);
it also protects against lung, liver, colon, pancreas, and skin cancers (Vigushin
et al. 1998; Crowell 1999; Setzer et al. 1999).
Linalool is a noncyclic monoterpenoid, commonly extracted from lavender
(Lavandula spp.), rose (Rosa spp.), and neroli oil (from Citrus aurantium). It
usually constitutes 5% or less of cannabis essential oil (Ross and ElSohly
1996). Linalool nevertheless exhibits strong biological activity. Buchbauer et
al. (1993) assayed the sedative effects of over 40 terpenoids upon inhalation
by mice; linalool was the most powerful, reducing mouse motility 73% after 1
hour of inhalation. The study demonstrated that other terpenoids found in can-
nabis, such as citronellol and α-terpineol, are also deeply sedating upon inha-
lation, even in low concentrations. Furthermore, combinations of these terpenoids
(e.g., neroli oil) are synergistic in their sedative effects. These terpenoids may
mitigate the anxiety provoked by pure THC. Inhalation of such terpenoids also
provides antidepressant effects (Komori et al. 1995).
Reducing anxiety and depression will improve immune function via the
neuroendocrine system, by damping down the hypothalamic-pituitary-adrenal
(HPA) axis. Hence, inhalation of terpenoids reduces the secretion of HPA
stress hormones (e.g., corticosterone), and normalizes CD4-CD8 ratios (Komori
et al. 1995). By a similar mechanism, terpenoids in Ginkgo biloba inhibit
116 CANNABIS THERAPEUTICS IN HIV/AIDS
corticosterone secretion by attenuating corticotropin-releasing factor (CRF)
expression (Marcihac et al. 1998). CRF not only induces corticosterone secre-
tion via the HPA axis, it is also associated with anxiety. Rodríguez de Fonseca
et al. (1996) showed that the psychoactive cannabinoid HU-210 caused a re-
lease of CRF. Thus, the terpenoids act synergistically with non-psychoactive
CBD, which may decrease CRF by inhibiting IFN-γ(Malfait et al. 2000).
Pulegone, a monocyclic monoterpenoid, is a minor constituent of cannabis
(Turner et al. 1980). Higher concentrations of pulegone are found in rosemary
(Rosmarinus officinalis), “the herb of remembrance.” Pulegone may alleviate
a major side effect of THC–loss of short-term memory consolidation. THC
causes acetylcholine (ACh) deficits in the hippocampus. Hippocampal ACh
deficits are also seen in people with Alzheimer’s disease. Alzheimer’s patients
can be treated with tacrine (Cognex), a drug that increases ACh activity by
inhibiting acetylcholinesterase (AChE). Indeed, tacrine has blocked THC-in-
duced memory loss behavior in rats. Pulegone exhibits the same activity as
tacrine, that of AChE inhibition (Miyazawa et al. 1997). Other terpenoids in
cannabis also provide AChE inhibition, including limonene, limonene oxide,
α-terpinene, γ-terpinene, terpinen-4-ol, carvacrol, l-and d-carvone, 1,8-cineole,
p-cymene, fenchone, and pulegone-1,2-epoxide (Perry et al. 1996; McPartland
and Pruitt 1999). The beneficial effects of AChE inhibitors, however, are de-
creased in individuals carrying the E4 subtype of the apolipoprotein E gene,
ApoE E4 (Poirier et al. 1995). Pulegone has also demonstrated significant sed-
ative and antipyretic properties in a study in rats (Ortiz de Urbina et al. 1989).
1,8-Cineole, a bicyclic monoterpenoid, is a minor constituent of cannabis
and the major aromatic found in Eucalyptus species. Studies show the inhala-
tion of 1,8-cineole increases cerebral blood flow and enhances cortical activity
(Nasel et al. 1994). Brain function is enhanced by administering terpenoids
that improve cerebral blood flow, much as the ginkgolides in Ginkgo biloba
(Russo 2000). Similarly, cerebral blood flow increases after inhaling cannabis
smoke, and this increase is not related to plasma levels of THC (Mathew and
Wilson 1993).
A stimulatory effect on rat locomotion was demonstrated employing a
1,8-cineole-rich essential oil of rosemary with a terpene profile similar to that
of cannabis (Kovar et al. 1987). Blood levels correlated with the degree of
stimulation observed. Antinociceptive and anti-inflammatory effects of 1,8-
cineole were demonstrated at high doses in rats, using carrageenan rat paw and
cotton pellet-induced granuloma models (Santos and Rao 2000). An analgesic
effect of an essential oil was demonstrated in another animal study, and corre-
lated with the 1,8-cineole concentration (Aydin et al. 1999).
1,8-Cineole demonstrated antibacterial activity against Bacillus subtilis,
and antifungal properties against Trichophyton mentagrophytes,Cryptococcus
neoformans, and Candida albicans (Hammerschmidt et al. 1993). In subse-
John M. McPartland and Ethan B. Russo 117
quent assays, this essential oil component was cidal against Candida albicans
and Escherichia coli, and bacteriostatic against Staphylococcus aureus (Car-
son and Riley 1995). In a rat study, 1,8-cineole prevented the sexual transmis-
sion of Herpes simplex virus type 2 (HSV-2). HSV-2 is a frequently comorbid
condition with HIV, and its prevention has been suggested as one method of
lowering HIV transmission risks (Gwanzura et al. 1998).
Perry et al. (2000) demonstrated that 1,8-cineole was an inhibitor of human
erythrocyte acetylcholinesterase, but that an essential oil of Salvia lavan-
dulaefolia containing 1,8-cineole and other terpenoids produced a synergistic
inhibition of acetylcholinesterase that suggested utility in the clinical treat-
ment of Alzheimer’s disease. A similar mechanism may operate in cannabis
essential oil with the same components.
α-Pinene, a bicyclic monoterpenoid, was effective in prevention of acute
inflammation in a carrageenan-induced plantar edema model (Gil et al. 1989).
A pharmacokinetics study of inhaled α-pinene in humans demonstrated 60%
uptake, and a relative bronchodilation effect (Falk et al. 1990). After 1 hour of
inhalation, α-pinene produced a 13.8% increase in mouse motility measures
(Buchbauer et al. 1993). α-Pinene has inhibited acetylcholinesterase in a vari-
ety of assays (Perry et al. 1996; McPartland and Pruitt 1999), suggesting utility
in the clinical treatment of Alzheimer’s disease. The antibiotic properties of
α-pinene, α-terpineol, and terpinen-4-ol have been demonstrated against
Staphylococcus aureus, S. epidermidis and Propionibacterium acnes (Raman
et al. 1995). α-Pinene and its isomer β-pinene were both cytotoxic in vitro
against Hep-G2 (human hepatocellular carcinoma) and Sk-Mel-28 (human
melanoma) tumor cell lines (Setzer et al. 1999).
α-Terpineol, terpinen-4-ol, and 4-terpineol are three closely related mono-
terpenoids. Inhalation of α-terpineol reduced mouse motility 45% (Buchbauer
et al. 1993). Burits and Bucar (2000) demonstrated that 4-terpineol exhibits
“respectable” radical scavenging and antioxidant properties. Terpinen-4-ol,
α-terpineol, and α-pinene demonstrated dose-dependent antibiotic properties
against Staphylococcus aureus, S. epidermidis and Propionibacterium acnes
(Raman et al. 1995). Similar studies have demonstrated antimicrobial activity
against a wide range of pathogenic organisms, excluding Pseudomonas (Car-
son and Riley 1995). Campbell et al. (1997) have demonstrated a moderate
antimalarial effect against two strains of Plasmodium falciparum by an essen-
tial oil with major α-terpineol and α-caryophyllene components.
Cymene, or p-cymene, a monoterpenoid, is active against Bacterioides
fragilis, Candida albicans, and Clostridium perfringens (Carson and Riley
1995).
118 CANNABIS THERAPEUTICS IN HIV/AIDS
Borneol, a bicyclic monoterpenoid, was tested in walnut oil as an external
treatment for purulent otitis media (Liu 1990), where it proved to be 98% ef-
fective (P < 0.001), to a greater degree than neomycin, and without toxicity.
∆3-Carene, a bicyclic monoterpenoid, was effective in prevention of acute
inflammation in a carrageenan-induced plantar edema model (Gil et al.
1989).
FLAVONOIDS
Flavonoids are aromatic, polycyclic phenols. Cannabis produces about 20
of these compounds, as free flavonoids and conjugated glycosides (Turner et
al. 1980). Paris et al. (1976) estimated that cannabis leaves consist of 1%
flavonoids. Some flavonoids are volatile, lipophilic, permeate membranes,
and apparently retain pharmacological activity in cannabis smoke (Sauer et al.
1983). Flavonoids may modulate the pharmacokinetics of THC, via a mecha-
nism shared by CBD, the inhibition of P450 3A11 and P450 3A4 enzymes.
Naringenin, a flavonoid in grapefruit juice, also inhibits these enzymes, thus
blocking the metabolism of cyclosporine, caffeine, benzodiazepines, and cal-
cium antagonists (Fuhr 1998). Two related enzymes, P450 3A4 and P450 1A1,
metabolize environmental toxins from procarcinogens to their activated forms.
Thus, P450-suppressing compounds serve as chemoprotective agents, shield-
ing healthy cells from the activation of benzo[α]pyrene and aflatoxin B1
(Offord et al. 1997), which are two procarcinogens potentially found in canna-
bis smoke (McPartland and Pruitt 1997).
Apigenin is a flavone found in nearly all vascular plants (Figure 3). It exerts
a wide range of biological effects, including many properties shared by
terpenoids and cannabinoids. Apigenin is the primary anxiolytic agent found
in chamomile, Matricaria recutita, (reviewed in Russo 2000). It selectively
binds with high affinity to central benzodiazepine receptors, which are located
in α- and β-subunits of GABAAreceptors (Salgueiro et al. 1997); this anxio-
lytic activity is not associated with the unwanted side effects caused by syn-
thetic benzodiazepines, such as muscular relaxation, amnesia, and sedation.
Apigenin inhibits the production of tumor necrosis factor-alpha (TNF-α), a
cytokine primarily expressed by monocytes and macrophages (Gerritsen et al.
1995). TNF-αinduces and maintains inflammation, a pathological condition
in rheumatoid arthritis and multiple sclerosis. THC decreases TNF-α, proba-
bly by a nonreceptor-mediated mechanism (Burnette-Curley and Cabral 1995),
although one study suggested THC might induce TNF-α(Shivers et al. 1994).
Either way, apigenin provides beneficial suppression of TNF-α, whether in
concert with THC or counteracting THC.
John M. McPartland and Ethan B. Russo 119
Apigenin and other flavonoids interact with estrogen receptors, and appear
to be the primary estrogenic agents in cannabis smoke (Sauer et al. 1983). Al-
though apigenin has a high affinity for estrogen receptors (especially β-estrogen
receptors), it has low estrogenic activity; apigenin actually inhibits estradiol-
induced proliferation of breast cancer cells (Wang and Kurzer 1998).
Quercetin is a flavonol found in nearly all vascular plants, including canna-
bis (Turner et al. 1980). Quercetin is a potent antioxidant; by some measures
more potent than ascorbic acid, α-tocopherol, and BHT (Gadow et al. 1997).
Combinations of quercetin and other antioxidants work synergistically (Hud-
120 CANNABIS THERAPEUTICS IN HIV/AIDS
FIGURE 3. Flavonoid and phytosterol components of cannabis.
Cannabis Constituent Structure* Concentration†Boiling
Point °C§Properties
apigenin > 0.1% 178 Anxiolytic
Antiinflammatory
Estrogenic
quercetin > 0.1% 250 Antioxidant
Antimutagenic
Antiviral
Antineoplastic
cannflavin A 0.02% 182 COX inhibitor
LO inhibitor
β-sitosterol ? 134 Antiinflammatory
5-α-reductase
inhibitor
OOH
OH
OH O
OOH
OH
OH O
OH
OH
OH
CH3
CH3
CH3
CH3
CH3
CH3
son and Mahgoub 1981). The antioxidant potential of quercetin and other
flavonoids should be tested against CBD, another potent antioxidant (Hampson
et al. 1998). Perhaps flavonoids can induce chemical reduction of CBD, effec-
tively recycling CBD as an antioxidant. Flavonoids block free radical forma-
tion at several steps: by scavenging superoxide anions (in both enzymatic and
non-enzymatic systems), by quenching intermediate peroxyl and alkoxyl radi-
cals, and by chelating iron ions, which catalyze many Fenton reactions leading
to free radical formation (Musonda and Chipman 1998).
Free radicals activate NF-κB, a transcription factor protein that induces the
expression of oncogenes, inflammation, and apoptosis. Quercetin arrests the
formation of NF-κB, by blocking the PKC-induced phosphorylation of an in-
hibitory subunit of NF-κB called IκB (Musonda and Chipman 1998), conse-
quently quercetin hinders carcinogenesis and inflammatory diseases. NF-κB
also plays a role in the activation of HIV-1 (Greenspan 1993), so quercetin
may hinder the replication of that virus. In a similar fashion, silymarin (a
flavonoid produced by milk thistle, Silybum marianum) impedes NF-κB-in-
duced replication of the hepatitis C virus, and thus inhibits hepatic carcinoma
(McPartland 1996). These flavonoids may synergize with CBN, which also
downregulates NF-κB (Herring and Kaminski 1999), thereby counteracting
the effects of THC, which may increase NF-κB activity (Daaka et al. 1997).
Cannflavin A is one of a pair of prenylated flavones apparently unique to
cannabis (Barrett et al. 1986). The yield of cannflavin A is 0.02% of dry herb.
This compound is a potent inhibitor of prostaglandin E2in human rheumatoid
synovial cells, with an IC50 of 31 ng/ml, about 30 times more potent than aspi-
rin in that system (Barrett et al. 1986). Cannflavin A inhibits cyclooxygenase
(COX) enzymes and lipoxygenase (LO) enzymes more potently than THC
(Evans et al. 1987). However, these assays were done with alcohol-extracted
cannflavin; we question whether cannflavin is sufficiently volatile. Other phe-
nols related to flavonoids are volatile and apparently retain pharmacological
activity in cannabis smoke, such as eugenol and p-vinylphenol (Burstein et al.
1976).
β-Sitosterol was demonstrated in significant concentrations in the red oil
extract of cannabis (Fenselau and Hermann 1972). In animal assays, this
phytosterol reduced acute inflammation 65% and chronic edema 40.6% (Gomez
et al. 1999). This agent has been the subject of most interest as the active ingre-
dient of Serenoa repens, the saw palmetto, and Urtica dioica, the nettle,
wherein β-sitosterol acts as a 5-α-reductase inhibitor. In numerous trials (Wilt
et al. 1998; McPartland and Pruitt 2000), standardized extracts of saw pal-
metto have proven equivalent or superior to finasteride in treatment of benign
prostatic hyperplasia.
John M. McPartland and Ethan B. Russo 121
CONCLUSIONS
Does the body absorb non-cannabinoids in physiologically relevant con-
centrations? In the absence of experimental data, we can estimate, using
limonene as an example of AChE inhibition. According to Ross and ElSohly
(1996), fresh, female flowering tops consist of 0.29% essential oil. Air drying
of female flowering tops decreases their moisture content (MC) from approxi-
mately 85% MC to 15% MC, with a concomitant loss in water weight
(McPartland and Pruitt 1997). Although some essential oil is volatilized and
lost in the drying process, the remaining terpenoids become concentrated. The
concentration of essential oil in air-dried cannabis is 0.8%, and limonene con-
sists of 17.2% of the essential oil (Ross and ElSohly 1996). Thus, air-dried
cannabis consists of 0.14% limonene; therefore a 500 mg cannabis cigarette
(which is half the size of a standard tobacco cigarette) would contain 0.7 mg
limonene. If we assume the systemic bioavailability of limonene from smok-
ing cannabis is 18%, the same as THC (Ohlsson et al. 1980), then 0.13 mg
would be absorbed. Distributing this dose evenly in the total body water of a 70
kg man, without metabolism or sequestration, would produce a maximum tis-
sue concentration of 1.3 µM. This concentration is an order of magnitude be-
low the IC50 concentration of limonene’s inhibition of AChE (Miyazawa et al.
1997). Hence, limonene must synergize with other AChE inhibitors in order to
be effective.
Vaporizer technology may improve the bioavailability of limonene and
other compounds, which volatilize around the same temperature as THC (see
Figures 1-3). Vaporizers are smoking apparati that heat cannabis to 185°C
(365°F), which vaporizes THC but is below the ignition point of combustible
plant material. Vaporized cannabis emits a thin gray vapor, whereas combusted
cannabis produces a thick smoke. Thus, vaporizers deliver a better canna-
binoid-to-tar ratio than cigarettes or water pipes (Gieringer 1996). In a recent
study, traces of THC were vaporized at temperatures as low as 140°C (284°F)
and the majority of THC vaporized by 185°C (365°F); benzene and other car-
cinogenic vapors did not appear until 200°C (392°F), and cannabis combus-
tion occurred around 230°C (446°F) (Gieringer 2001).
Concerning bioavailability, it should be mentioned that cannabis com-
pounds need not be absorbed systemically through the lungs to produce CNS
activity. Inhaled compounds may reach receptors in the olfactory bulb, send-
ing mood-altering messages via olfactory nerves directly to the limbic region
and hippocampus. This route may be responsible for some sedative effects of
terpenoids upon inhalation (Buchbauer et al. 1993).
The paucity of research concerning non-THC synergists in cannabis is peri-
odically criticized (Mechoulam et al. 1972; McPartland and Pruitt 1999; Russo
2000). We have highlighted several cannabinoids, terpenoids, and flavonoids
122 CANNABIS THERAPEUTICS IN HIV/AIDS
that deserve further attention regarding their contributions to the effects of
clinical cannabis. Most of the data we present here is based on in vitro experi-
ments or animal studies. Clearly the next step should involve human clinical
trials of each constituent, alone, or in combination with THC, or combined
with a cocktail of cannabis compounds.
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