Phytocannabinoids are naturally occurring active compounds from plants of the genus Cannabis that act on the human endocannabinoid system. Apart from the best known phytocannabinoids THC and CBD, cannabis also contains other pharmacologically active substances (including terpenes), some of which work together in a synergistic manner. When the pharmacological properties of a complete plant extract exceed the properties of each fraction alone and effectively 1 + 1 adds up to 3, this is due to the “entourage effect” of the contained active substances. The entourage effect is exploited in the phytotherapeutic approach to pharmacotherapy

What are phytocannabinoids?

Phytocannabinoids (Phyto = Greek for plant) are naturally occurring lipophilic (fat-soluble) terpene phenols and their transformation products derived from the genus Cannabis (hemp), a mostly annual herbaceous plant. Cannabinoids have also been detected in other plants (e.g. hops and echinacea).1  The term cannabinoid refers to a family of molecules that have binding affinity to the body’s endocannabinoid receptors CB1 and CB2. THC and CBD are the most biologically active phytocannabinoids that, when consumed, mimic human endocannabinoids such as anandamide (AEA) and 2-arachidonoylglycerol (2-AG) at their receptor binding sites.2 Over 100 different phytocannabinoids have been discovered so far.3

How are Phytocannabinoids synthesized?

Phytocannabinoids are synthesized together with terpenes (the main component of essential oils) in secretory cells within glandular trichomes and reach the highest concentration in unfertilized female flowers of the cannabis plant. The common raw material for the synthesis of cannabinoids and terpenoids is geranyl pyrophosphate (geranyl-PP or GPP).4 Through enzymatic conjugation of GPP and olivetoleic acid, cannabigerolic acid (CBGA) is formed, from which subsequently CBG (cannabigerol), THCA (tetrahydrocannabinol acid), CBDA (cannabidiol acid) or CBCA (cannabichromene acid) are synthesized, among others. In the plant, the cannabinoids are predominantly present in the form of their acidic precursors as carboxylic acids (instead of THC e.g. THCA; A stands for acid). Under the influence of heat, light or during long-term storage, these acidic precursors are converted into their neutral, pharmacologically more active forms by decarboxylation – i.e. removal of CO2 – as an example, the weak CB1 receptor agonist THCA becomes the potent CB1 receptor agonist THC.5
Rasin glands Cannabis (Trichome)

Which Phytocannabinoids exist and what is their pharmacological effect?

The most well-known cannabinoid is the psychotropic Δ9-tetrahydrocannabinol (Δ9-THC), which was isolated in 1964 by Yehiel Gaoni and Raphael Mechoulam at the Weizmann Institute of Science in Israel.6

THC (mainly antiemetic, relaxing, sedating) unfolds its effect predominantly as an agonist of CB1 and CB2 receptors of the endocannabinoid system (ECS). The main function of the ECS is, among other things, the inhibition of release of various neurotransmitters.

Neurotransmitter Associated Dysfunction
Excitatory Amino Acids
Glutamate Epilepsy, neuronal cell death in ischemia and hypoxia (stroke, traumatic brain injury, nerve gas damage)
Inhibitory Amino Acids
GABA Disorders of spinal cord function, epilepsy
Glycine Hyperekplexia and other syndromes with exaggerated startle response
Norepinephrine Autonomous homeostasis, hormones, depression
Serotonin depression, anxiety, migraine, vomiting
Dopamine Parkinsons Disease, schizophrenia, vomiting, pineal hormones, addiction
Acetylcholine Neuro-muscular disorders, autonomous homeostasis (heart rate, blood pressure), dementia, parkinsonism, epilepsy, circadian rythm
Neuropeptides (endorphins, enkephalins) Pain, movement, neural development, anxiety
Table 1. Functions of the neurotransmitters under control of the ECS (Table from the Book "Cannabis Verordnungshilfe für Ärzte. Grotenhermen Häusermann")

In simplified terms, CB1 receptors are expressed in the central nervous system, gastrointestinal tract, fat cells, liver parenchyma and skeletal muscle; and CB2 receptors mainly on immune cells.2

The second most common cannabinoid in medicinal hemp, cannabidiol (CBD – mainly antipsychotic, anxiolytic, anti-inflammatory, antiemetic, spasmolytic), is not psychotropic and acts in part indirectly through modulation of the THC/CB2 receptor interaction.

Further mechanisms of action have been discovered for CBD – among others, it shows an agonistic binding affinity to the serotonin receptor 5-HT1 and the receptor GPR55 (potentially the CB3 receptor of the ECS), as well as an antagonistic effect on the μ-opioid receptor.7

It is particularly noteworthy that CBD significantly reduces the psychotropic effects of THC and is therefore now being discussed as a potential antipsychotic medication in scientific literature. Furthermore, for other phytocannabinoids from cannabis, including tetrahydrocannabivarin, cannabigerol and cannabichromene, further therapeutic applicability has been experimentally demonstrated, (e.g., neuroprotective, anti-inflammatory or modulatory properties).8,9,10

The terpenes (main constituent of essential oils) also seem to be important players in the entire “orchestra” of cannabis pharmacology; it is also well known outside cannabis research that the fragrance of limonene (terpene found in cannabis and citrus fruits), for example, improves mood and that myrcene (terpene found in cannabis and hops) is relaxing.

Dr. Ethan B. Russo published a review in the British Journal of Pharmacology in 2011 on the synergistic effects of phytocannabinoids and terpenes. The following overview is taken from this work:

Phytocannabinoid Structure Selected pharmacology (reference) Synergistlc terpenolds
THC delta9-tetrahydrocannabinol (THC) Analgesic via CB1, and CB2 (Rahn and Hohmann, 2009) Various
Al/antioxidant (Hampson et al., 1998) Limonene et al.
Bronchodilatory (Williams et al., 1976) Pinene
↓ Sx. Alzheimer disease (Volicer et al., 1997; Eubanks et al., 2006) Limonene, pinene, Linalool
Benefit on duodenal ulcers (Douthwaite, 1947) Caryophyllene, Limonene
Muscle relaxant (Kavia et al., 201 0) Linalool?
Antipruritic, cholestatic jaundice (Neff et al., 2002) Caryophyllene?
CBD CBD Al/antioxidant (Hampson et al., 1998) Limonene et al.
Anti-anxiety via 5-HT1A (Russe et al., 2005) Linalool, limonene
Anticonvulsant Oones et al., 2010) Linalool
Cytotoxic versus breast cancer (Ligresti et al., 2006) Limonene
↑ adenosine A2A signalling (Carrier et al., 2006) Linalool
Effective versus MRSA (Appendino et al., 2008) Pinene
Decreases sebum/sebocytes (Biro et al., 2009) Pinene, Limonene, Linalool
Treatment of addiction (see text) Caryophyllene
CBC CBC Anti-inflammatory/analgesic (Davis and Hatoum, 1983) Various
Antifungal (EISohly et al., 1982) Caryophyllene oxide
AEA uptake inhibitor (De Petrocellis et al., 2011) -
Antidepressant in rodent model (Deyo and Musty, 2003) Limonene
CBG CBG TRPM8 antagonist prostate cancer (De Petrocellis et al., 2011) Cannabis terpenoids
GABA uptake inhibitor (Banerjee et al., 1975) Phytol, Linalool
Anti-fungal (EISohly et al., 1982) Caryophyllene oxide
Antidepressant rodent model (Musty and Deyo, 2006); and via 5-HTIA antagonism (Cascio et al., 2010) Limonene
Analgesie, α-2 adrenergic blockade (Cascio et al., 2010) Various
↓ keratinocytes in psoriasis (Wilkinson and Williamson, 2007) adjunctive role?
Effective versus MRSA (Appendino et al., 2008) Pinene
Al/anti-hyperalgesic (Bolognini et al., 2010) Caryophyllene et al. . . .
THCV THCV Treatment of metabolic syndrome (Cawthorne et al., 2007) -
Anticonvulsant (Hilf et al., 2010) Linalool
CBV CBV lnhibits diacylglycerol lipase (De Petrocellis et al., 2011) -
Anticonvulsant in hippocampus (Hill et al., 2010) Linalool
CBN CBN Sedative (Musty et al., 1976) Nerolidol, Mycrene
Effective versus MRSA (Appendino et al., 2008) Pinene
TRPV2 agonist for burns (Qin et al., 2008) Linalool
↓ keratinocytes in psoriasis (Wilkinson and Williamson, 2007) adjunctive role?
↓ breast cancer resistance protein (Holland et al., 2008) Limonene
Table 2. 5-HT, 5-hydroxytryptamine (serotonin); AEA, arachidonoylethanolamide (anandamide); AI, anti-inflammatory; CB1/CB2, cannabinoid receptor 1 or 2; GABA, gamma aminobutyric acid; TRPV, transient receptor potential vanilloid receptor; MRSA, methicillin-resistant Staphylococcus aureus; Sx, symptoms.

Monotherapy vs. Phytotherapy - What is the Entourage Effect?

There is a fundamental difference between a monotherapeutic and a phytotherapeutic approach in pharmacotherapy: monotherapy works with one or a few isolated or chemically designed novel components to target a molecule or a single signaling pathway known to be involved in a disease. Since all physiological processes in the body are ultimately intertwined however, unforeseen (and at first sight unrelated) side effects often occur.

In the phytotherapeutic approach, a mixture of active ingredients is used, its clinical effects (including side effects) being well-known from sometimes millennia of ongoing observation and tradition – not only from in vitro or in vivo models of diseases, but humans – and science examines in detail which molecules and signaling pathways are involved in the following.

In the case of cannabis, whose broad spectrum of activity and favorable safety profile has been known for 5,000 years, Carlini et al. as early as 1974 demonstrated that cannabis extracts can be two to four times more effective than THC alone.4

If the pharmacological properties of a complete plant extract act synergistically in a way that effectively 1 + 1 = 3, then this is the so-called “entourage effect” of the contained active ingredients: In addition to the known active ingredients, other undefined components in the mixture seem to contribute to its enhanced efficacy. Experts call medical cannabis a prime example for this effect.

There are various hypotheses for the explanation:
a) It is possible that the different active ingredients simultaneously influence several signaling pathways in the same symptom complex (“multi-target”), b) that the active ingredients mutually influence each other’s solubility or bioavailability and therefore also influence pharmacokinetics, c ) that interactions between the active ingredients increase the bacterial resistance of the whole organism and d) that adverse reactions are balanced out by the presence of agonists or antagonists with variant binding affinity for the receptors. For example, CBD reduces the intoxicating effect of THC but enhances its inhibitory effect on tumor cell growth (in vitro); THC and CBD also show a synergistic effect in pain treatment (in vivo).4,11,12

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[2]  Mouhamed Y, Vishnyakov A, Qorri B, et al. Therapeutic potential of medicinal marijuana: an educational primer for health care professionals. Drug Healthc Patient Saf. 2018;10:45-66. doi:10.2147/DHPS.S158592

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[5] Info-Broschüre: Medizinisches Cannabis Aspekte und Wirkungsweise von Dr. Arno Hazekamp

[6] Y. Gaoni, R. Mechoulam: Isolation, Structure, and Partial Synthesis of an Active Constituent of Hashish. In: Journal of the American Chemical Society. 86, 1964, S. 1646, doi:10.1021/ja01062a046


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[11] Pamplona FA, daSilva LR, Coan AC. Potential clinical benefits of CBD-rich Cannabis extracts over purified cannabidiol (CBD) in treatment-resistant epilepsy: observational data meta-analysis. Front Neurol. 2018;9:759. doi:10.3389/FNEUR.2018.00759

[12] Blasco-Benito S, Seijo-Vila M, Caro-Villalobos M, et al. Appraising the “entourage effect”: Antitumor action of a pure cannabinoid versus a botanical drug preparation in preclinical models of breast cancer. Biochem Pharmacol. June 2018. doi:10.1016/j.bcp.2018.06.025

[13] Marcu JP, Christian RT, Lau D, et al. Cannabidiol enhances the inhibitory effects of delta9-tetrahydrocannabinol on human glioblastoma cell proliferation and survival. Mol Cancer Ther. 2010;9(1):180-189. doi:10.1158/1535-7163.MCT-09-0407

[14] Casey S, Vaughan C. Plant-Based Cannabinoids for the Treatment of Chronic Neuropathic Pain. Medicines. 2018;5(3):67. doi:10.3390/medicines5030067