Introduction

An enduring notion in the medicinal Cannabis and cannabinoid field is that of entourage: the idea that use of the whole plant may exert substantially greater effects than the sum of its individual parts.¹ Entourage is usually construed as a positive attribute, with the assumption that superior therapeutic actions, or a more favorable “high,” will be obtained from consuming the whole Cannabis plant rather than individual components such as Δ⁹-tetrahydrocannabinol (Δ⁹-THC). Somewhat surprisingly, the evidence for this widely cited notion is relatively sparse.

Cannabis contains ∼150 phytocannabinoids, the most common of which are Δ⁹-THC and cannabidiol (CBD), together with their acid precursors THCA and CBDA.²Cannabis also contains a large number of monoterpene and sesquiterpene compounds (together called terpenoids), the most common of which include α-pinene, β-pinene, linalool, limonene and β-myrcene (monoterpenes) and β-caryophyllene and caryophyllene oxide (sesquiterpenes).³ Terpenoids are volatile compounds that are synthesized alongside phytocannabinoids mainly in the trichomes of the cannabis plant, and provide cannabis with its distinctive aroma and flavor.⁴ Terpenoids are often lost if the extraction process involves heating.⁵

The entourage concept applied to cannabis can encompass the potential for both cannabinoid–cannabinoid and cannabinoid–terpenoid interactions. With regard to the former, Δ⁹-THC-CBD synergy in producing analgesia was reported in an animal model of neuropathic pain⁶ while in humans, CBD has been proposed to ameliorate some of the adverse psychotomimetic and anxiogenic effects of Δ⁹-THC.^7,8 This claim is controversial, however, with a number of contrary findings.^9,10 CBD may modulate Δ⁹-THC effects at the receptor level acting as a CB₁ negative allosteric modulator,¹¹ providing some biological plausibility to a modulatory interaction.

Scientific evidence for cannabinoid–terpenoid interactions is essentially absent, and mostly comes from websites and dispensaries extolling the virtues of proprietary Cannabis chemical varieties, or chemovars.^12,13 However, some terpenoids do have intrinsic psychoactive and physiological effects, and modulatory effects on Δ⁹-THC actions are not farfetched.^1,14 For example, in studies with laboratory animals, limonene displayed anxiolytic effects, pinene increased gastrointestinal motility, linalool was sedative, anticonvulsant, and anxiolytic, while myrcene produced sedation, analgesia, and muscle relaxant effects (summarized in Russo and Marcu¹⁴). Lewis et al.¹³ reported that in a low terpenoids variety (1.1% terpenoids) myrcene concentration is 0.45%, while in a high variety (4.8% total) myrcene concentration is as high as 3.44%. Compelling evidence for cannabinoid–terpenoid interactions or synergy does not yet exist. A report on perceived efficacy of Cannabis for childhood epilepsy identified the presence of three predominant terpenoids (β-caryophyllene, β-myrcene, and α-pinene); however, when extracts perceived as “effective” were compared with “ineffective” extracts, differences in terpenoid profile/content were not significant.¹⁵

With so many bioactive components present in cannabis, the systematic, granular elucidation of possible entourage effects poses a substantial combinatorial puzzle and scientific challenge. As a preliminary approach to addressing this challenge, this study examined whether the effects of Δ⁹-THC on its cognate cannabinoid receptors (CB₁ and CB₂) would be modified in the presence of terpenoids that are commonly found in cannabis, either alone or in combination. The demonstration of such a receptor-level entourage effect might lead to predictions regarding functional cannabinoid–terpenoid interaction effects that could be tested in vivo.

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