Between Science and Big Business: Tapping Mary Jane’s Uncharted Potential

2.1. Cannabinoid Receptors

The endogenous cannabinoid system consists of so far two identified G-protein coupled receptors (GPCRs), CB₁ and CB₂ that were named after their affinity for the agonist Δ⁹-THC.^32,33 Both CB₁ and CB₂ are coupled through the G_i/o family of proteins and are expressed both in the CNS and the immune system.³³⁻³⁵

CB₁ was first cloned by Tom Bonner’s lab in 1990.¹⁶ Autoradiographic studies have shown that CB₁ can be found mainly in the cerebral cortex, hippocampus, basal ganglia, and cerebellum—regions that are consistent with the known effects of cannabinoids on motivation and cognition.^16,34,36 Indeed, the physiological responses generally associated with Δ⁹-THC consumption such as reduced stress, increased appetite, and euphoria, are generally attributed to activation of CB₁ receptors.³⁷⁻³⁹

The CB₂ receptor was first cloned in 1993 at the MRC Laboratory of Molecular Biology in Cambridge, England, and has a 44% sequence identity with CB₁.^17,32 Immunocytochemical evidence has identified the presence of CB₂ in spleen, thymus, tonsils, bone marrow, pancreas, mast cells, peripheral blood leukocytes, and several cultured immune cell models.^33,41 Although CB₂ is expressed mainly in the immune system, it is also present in the CNS, where it has been shown to control synaptic function and regulate synaptic plasticity, making it highly relevant target for many neurological disorders.^42,43

2.2. Endocannabinoids

By inference, the presence of cannabinoid receptors indicates the existence of endogenous molecules that have the ability to modulate those receptors. These effects are mainly attributed to the two eicosanoids, AEA and 2-AG (Figure​Figure11a).⁴⁴⁻⁴⁷ The endocannabinoids (eCBs) are lipophilic, and, unlike most neurotransmitters, they are not stored in vesicles but rather synthesized “on demand” from membrane phospholipids as a result of increased intracellular Ca²⁺ levels at the postsynaptic site.^42,48 Their action is generally presynaptic rather than postsynaptic, meaning that once at their target site, eCBs bind to CB₁ receptors located at the presynaptic site in a retrograde manner, suppressing neurotransmitter release (Figure​Figure11b).^33,48 Although they are inherently quite similar, the two ligands exhibit distinct functions in the ECS. While both AEA and 2-AG regulate presynaptic neurotransmitter release, the molecules mediate short-term and long-term synaptic plasticity in the brain by operating in phasic and tonic modes.⁴⁹ The available evidence suggests that AEA acts as the tonic signaling molecule, adapting slowly to stimulus and firing a sustained response, whereas 2-AG represents the phasic signal, adapting rapidly to stimulus and producing a more transient response during neuronal depolarization.⁴⁹ After the desired homeostatic response has been achieved, both AEA and 2-AG are removed from the synapse and degraded by their respective hydrolytic enzymes.⁴⁹

Figure 1

(a) Structures of the known phytocannabinoids Δ9-tetrahydrocannabinol (Δ9-THC) and cannabidiol (CBD), as well as the endogenous cannabinoids anandamide (AEA) and 2-arachidonyl glycerol (2-AG). (b) Schematic representation of the main components of the endocannabinoid system within the central nervous system (CNS). Here, glutamate release activates the NMDA receptor, leading to increased cytoplasmic calcium levels. Subsequently, the enzyme NAPE-PLD catalyzes the synthesis of AEA from NAPE, and DAGL catalyzes the synthesis of 2-AG from DAG. Release of AEA and 2-AG into the synaptic cleft triggers the activation of CB receptors at the presynaptic site and inhibits further neurotransmitter release. Once homeostasis is achieved, the endogenous cannabinoid molecules are degraded by their respective enzymes.

2.3. Enzymes

Synthesis of 2-AG and other monoacylglycerols is catalyzed by diacylglycerol lipase α (DAGLα), and synthesis of anandamide and other N-acylethanolamines is catalyzed by N-acylphosphatidylethanolamine (NAPE)-specific phospholipase D-like hydrolase (NAPE-PLD).^50,51 The most notable and well-understood degradation enzymes in the endocannabinoid system are fatty acid amide hydrolase (FAAH) and monoacylglycerol lipase (MAGL), which hydrolyze AEA and 2-AG, respectively.^52,53 Experimental evidence indicates that FAAH is located primarily on the intracellular membrane of postsynaptic cells, whereas MAGL is generally located in presynaptic terminals in the vicinity of CB₁ receptors.^54,55

2.4. Role of the Endocannabinoid System in the CNS

Entering the neurochemical, psychological, and philosophical realm of discussion, we are faced with three important questions about the endocannabinoid system: how do these components interact with each other to produce a physiological response?, why, from an evolutionary standpoint, do they work in this manner?, and to what effect do they influence our behavior?

To answer these questions, we must closely examine the known mechanisms of endocannabinoid signaling (Figure​Figure11b). As previously mentioned, endogenous cannabinoids act as retrograde messengers to suppress neurotransmitter release. In other words, endocannabinoids are synthesized “on-demand” in response to neuronal stimulation and suppress the release of chemicals such as glutamate and GABA.^56,57 In essence, this molecular mechanism outlines the process of endocannabinoid-mediated synaptic plasticity.⁵⁸ The evidence for this is overwhelming, as three independent research groups in the early 2000s reported that postsynaptic depolarization-induced Ca²⁺ elevation in the hippocampus and cerebellar cortex triggers the postsynaptic synthesis of endogenous cannabinoids, which proceed to inhibit CB₁-mediated neurotransmitter release at the presynaptic site.⁵⁹⁻⁶¹ Since the early 2000s, eCBs have been shown to activate both short-term (depolarization-induced suppression of inhibition/excitation, or DSI/DSE) and long-term plasticity (long-term depression, or LTD) at synapses throughout the brain.^58,62 The most important and well-explored of these phenomena is LTD, which is defined by the reduction in neurotransmitter release upon binding of eCBs to CB₁ and has been reported in the dorsal striatum, nucleus accumbens, amygdala, and hippocampus among others.⁶³⁻⁶⁸ The exact mechanisms underlying these changes are highly complex and still not fully understood. However, it is known that endocannabinoid-mediated LTD is a fundamental mechanism for inducing long-term changes to neural circuits and behavior.⁶² Simply put, the endocannabinoid system exists to provide on-demand protection against excitotoxicity in CNS neurons.⁶⁹

This brings us to the second question regarding the evolutionary purpose of the endocannabinoid system as a protective mechanism against fear, anxiety, and stress. Fear and anxiety are natural phenomena that occur as a result of a real or perceived threat, or the possibility of such a threat arising in the future.^18,40 Similarly, the stress response is a bodily reaction to this challenge in order to prepare it for upcoming danger, functioning as a protective mechanism that is essential to an organism’s survival.⁴⁰ The body’s response to stress consists of an autonomic and a neuroendocrine responses that are activated in parallel.¹⁸ The autonomic nervous system consists of the sympathetic and parasympathetic nervous system, and functions mainly by using catecholamines like norepinephrine and acetylcholine as neurotransmitters.⁷⁰ In contrast, the neuroendocrine system is mediated by activation of the hypothalamic pituitary adrenal (HPA) axis, releasing cortisol, corticotropin, and other corticosteroids.⁷⁰ Although these mechanisms are integral in delegating the basic survival instinct, superfluous response to external stressors, especially when chronic, can prove detrimental to cognitive health and incite a shift in several neurobehavioral responses including anxiety, memory, pain sensitivity, and coping behaviors.^18,71,72 Therefore, it is vital that the domains of fear, anxiety, and stress are regulated by the endocannabinoid system in an effort to maintain homeostasis in a healthy brain.⁴⁰

Lastly, it is important to touch upon the effects of endocannabinoid-mediated synaptic plasticity on human behavior. Several clinical and preclinical studies have been conducted in an effort to explore how the ECS acts as a buffer against the effects of stress. As previously discussed, the ECS controls several brain regions related to fear and anxiety, generally regulating overactivation. Acute exposure to stress results in an increase of FAAH activity and thus a reduction of AEA levels in the amygdala and prefrontal cortex. This leads to activation of the HPA axis and an increase in the concentration of 2-AG, which in turn inhibits the release of glutamate and GABA in the hypothalamus and prefrontal cortex, respectively.^40,73,74 However, the repeated exposure of the brain to nonhabituating, chronic stress results in desensitization of CB₁ receptor signaling.^40,75 This becomes important as chronic stress can trigger or exacerbate a variety of psychiatric disorders including schizophrenia and major depressive disorder (MDD).^76,77

3.1. Δ⁹-Tetrahydrocannabinol (Δ⁹-THC)

In 1964, Gaoni and Mechoulam reported the isolation of Δ⁹-THC as the first structurally elucidated active component of Cannabis sativa.¹³ There are several constitutional and stereoisomers of THC, but (−)-trans-Δ⁹-tetrahydrocannabinol or (6aR, 10aR)-delta-9-tetrahydrocannabinol is the main plant-derived isomer and, by extension, also the most well explored. Interestingly, it is far less stable than its Δ⁸ and Δ¹⁰ analogues, with Δ¹⁰ being the most stable as a result of the double bond in conjugation with the aromatic ring (Figure​Figure33).

Δ⁹-THC acts as a partial agonist on both CB₁ and CB₂, with K_i values in the low nanomolar range.⁸⁸ The psychoactive effects of Δ⁹-THC are mediated by CB₁, and its potential immunological or anti-inflammatory effects are thought to be a result of CB₂ receptor agonism.⁸⁹ The effects of this molecule are fairly well studied, but the complexity of the interactions leaves several questions open. Effectively, it is known that Δ⁹-THC perturbs GABA and glutamatergic neurotransmission in a similar fashion to endogenous cannabinoids, producing many of the common effects associated with consumption of cannabis.^88,89 Notably, however, neuronal CB₁ receptors are targeted in a less selective manner by phytocannabinoids than the respective endogenous cannabinoids.⁸⁹ Emerging evidence over the last two decades has shown that in vivo administration of Δ⁹-THC can actually increase the release of certain neurotransmitters, i.e., acetylcholine in rat hippocampus, acetylcholine, glutamate, and dopamine in rat prefrontal cortex, and dopamine in mouse and rat nucleus accumbens.⁸⁹⁻⁹¹ These combined stimulatory–inhibitory influences could be responsible for the excitant and depressant effects of Δ⁹-THC.^92,93

The implications of Δ⁹-THC administration on psychosis, addiction, and memory and cognition remain controversial. Generally, cognitive deficits observed from acute exposure to cannabis are transient.^88,94 In contrast, prolonged use is associated with more pronounced chronic deficits in learning and memory.⁹⁵ It is worth noting that more recent studies have not replicated this conclusion.^96,97

3.2. Cannabidiol (CBD)

(−)-Cannabidiol (CBD) is the second major constituent of Cannabis sativa. It was first isolated in 1940 by Adams and co-workers, but its structure was not fully elucidated until almost 30 years later when Mechoulam’s group was able to isolate CBD from Lebanese hashish and establish its structure and stereochemistry.^14,15,98 It differs from the THC in that it has a pyran ring and can easily undergo acid- and base-catalyzed transformations to produce Δ⁹-THC and Δ⁶-CBD, respectively (Figure​Figure44).⁹⁸

Although structurally similar to Δ⁹-THC, CBD exhibits none of the addictive or psychoactive properties associated with its infamous relative and is known to have very low affinity to both known cannabinoid receptors. This lack of affinity seems to be a result of the two rings in CBD being oriented in a perpendicular fashion, as compared to the planar conformation of Δ⁹-THC.⁹⁹ Unlike the endogenous cannabinoids and Δ⁹-THC, CBD possesses a highly complex and diverse pharmacological profile, relying on interactions with a myriad of receptors. Here, we will highlight only the most important interactions. One known mechanism of cannabidiol action is its function as an antagonist of cannabinoid receptor agonists.¹⁰⁰ It was able to block the effects of CB₁ agonists WIN55212 and CP55940 at a far lower dose than is required for receptor activation by CBD. Studies have also shown that it enhances endogenous adenosine signaling through inhibition of uptake, providing an explanation for its anti-inflammatory properties.^101,102 In addition, CBD is a modest agonist of the serotonin (5-HT_2A) receptor, which may be responsible for its analgesic and anxiolytic effects.¹⁰³ It is also a potent antioxidant, as studies by Hampson et al. have shown that CBD prevents hydrogen peroxide-induced oxidative damage as well as or better than vitamin C and vitamin E.¹⁰⁴ Furthermore, there is evidence for activity at the δ- and μ-opioid receptors and TRPV1 cation channels.⁸⁹

CBD has a well-established safety profile and generally is well tolerated in doses up to 1500 mg/day orally, without any reported negative effects on mood or motor skills.¹⁰⁵ Evidence from human studies has highlighted the potential of CBD for treatment against anxiety at 300–600 mg PO daily.²⁰ With this in mind, interest in the therapeutic potential of cannabidiol has skyrocketed over the past decades. Increasing amounts of preclinical and clinical data have been gathered to support the application of CBD as an antipsychotic, analgesic, antiemetic, antioxidant, antiepileptic, anti-inflammatory, and anticonvulsant.^20,88

3.3. Approved Cannabinoids

The only two pharmaceutical forms of Δ⁹-THC on the U.S. market are nabilone (a synthetic derivative of Δ⁹-THC) and dronabinol (synthetic Δ⁹-THC).¹⁰⁶ Both medications are used in the treatment of chemotherapy-related nausea and AIDS-associated weight loss and anorexia.⁸⁸ On June 25, 2018, the FDA approved Epidiolex, a highly purified botanical CBD extract, for the treatment of Dravet syndrome and Lenox Gastaut syndrome, two forms of childhood-onset epilepsy.^12,107 Almost a decade after a study conducted by the lab of Ben Whalley highlighted the antiseizure properties of cannabidiol, Epidiolex is the first cannabis-derived medicine approved for clinical use. The only currently approved combined formulation, Sativex, contains a 1:1 ratio of CBD/Δ⁹-THC.¹² Interestingly, users have oftentimes described vastly different sensations based on whether the administered drug was synthetic or plant-derived, although the two were chemically identical.¹²

3.4. Entourage Effect

Here lies the pressing question: how can two chemically identical compounds produce different effects based purely on the method of their isolation? Given that chemistry is an exact science and spectroscopic methods can confirm the identity of the molecules in question, there are only two scenarios that could explain this phenomenon: (a) one of the substances was mistakenly identified, or (b) one of the substances contains an impurity that contributes to the overall pharmacological profile.¹² The so-called “entourage effect” provides a strong case for the latter and was first described by Ben-Shabat in 1998 with reference to the enhanced activity of the endogenous cannabinoid 2-AG by inactive fatty acid glycerol esters.¹⁰⁸ Since then, the term has been extended to incorporate other cannabinoids and noncannabinoids that enhance the activity of cannabis preparations.¹⁰⁹ As stated by Mechoulam, “this type of synergism may play a role in the widely held view that in some cases, plants are better drugs than the natural products isolated from them”.¹¹⁰

At this stage, it is only logical to ask: what therapeutic advantage, if any, does utilizing the entire cannabis plant provide as opposed to the government-approved synthetic formulations like dronabinol? One indication that the nonpsychoactive components of the cannabis plant alter the physiological response is demonstrated by the markedly different effects of the Cannabis sativa and Cannabis indica chemovars.¹¹¹ Although both contain Δ⁹-THC, the former tends to enhance creativity and productivity, while the latter is known to induce relaxation. As a matter of fact, the disparities between the different chemovars are so significant that the species assignation of cannabis itself is subject to heavy debate.¹¹¹ The question remains: why do cannabis users experience such divergent strain-dependent sensations if the main active ingredient is the same?

Since the original discovery of the entourage effect, it has been shown on several occasions that THC monotherapy is not as effective as the dual administration of THC in combination with CBD or terpenoids.¹⁰⁹ In 2010, Johnson and co-workers conducted a multicenter, double-blind, randomized placebo-controlled study of cannabis-based extracts in patients with cancer-related pain.¹¹² In their findings, the THC-predominant extract produced results similar to the placebo, whereas a plant extract containing a mixture of CBD and THC was statistically significantly better than both.^111,112 In another study, researchers found that small doses of pure CBD reduce pain until a peak is reached, after which further increases are ineffective.¹¹³ This bell-shaped dose–response curve was, however, not observed for a full-spectrum cannabis extract with equivalent doses of CBD, which resulted in a linear dose–response curve with no observed ceiling effect.¹¹³ Thus, counterintuitively, higher purity formulations of the active ingredients in cannabis did not guarantee higher therapeutic efficacy. Further evidence for the entourage effect was provided by a study conducted in 2018, which employed five distinct cannabis extracts with a uniform concentration of CBD on mice with induced seizures.¹¹⁴ The results of this study showed that all five extracts were beneficial when compared to the control, but there were pronounced differences between the number of mice developing tonic-clonic seizures (21.5–66.7%) as a result of the varying amounts of the “minor” components in each extract.^111,114 In summary, these findings show that isolating or synthesizing only the active components of marijuana may significantly limit the plant’s therapeutic potential and, by extension, limit the variability of interbreeding and hybridization within the highly versatile cannabis genome.

Currently, the lack of hard scientific evidence to back these empirical findings limits the utility of the entourage effect in therapeutic applications.¹¹⁵ Neither the effects of cannabinoid–cannabinoid interactions nor the effects of cannabinoid–terpenoid interactions have been clearly elucidated. If there are to be significant advances in cannabinoid-based drug discovery, it is essential that more comprehensive studies are designed and performed to gather conclusive scientific evidence.

4.1. The Tangled History of Cannabis

What is the reason for this lack of progress? And why has cannabinoid-based drug development been so stagnant in comparison to opioids? With the introduction of cannabis, opium, and coca into Western culture at a time of rapid technological and scientific developments, the blurred lines between religious, social, and medicinal uses of these plants became ever more defined.¹²⁹ However, early efforts to identify and isolate the active components of cannabis for medicinal purposes proved to be too big of a challenge for the state of knowledge at the time.¹³⁰ Availability of other therapeutics discouraged physicians from prescribing such preparations, and cannabis was swept under the rug as a useless remedy. Henceforth, cannabis became looped into the efforts to eliminate illegitimate use of drugs under a series of international drug conventions in the early 20th century. The results of this have shaped the portrayal of cannabis in popular culture, as well as efforts in science up to this day (Figure​Figure55).

Figure 5

A select timeline of the history of cannabis as medicine.

4.2. Regulatory Status and Academic Research

In the United States, federal law prohibits the possession, production, and distribution of cannabis. The Controlled Substance Act (CSA) of 1970 lists cannabis (in the form of resin, extracts, tincture, pure THC, and pure CBD) as a Schedule I drug with no medical use, in the same category as heroin and worse than methamphetamine and cocaine.^129,131,132 As a consequence, obtaining permission to conduct clinical research on cannabis is a lengthy process and requires approval from both the FDA and the DEA.¹³³ In addition, all cannabis used for research purposes must be obtained exclusively from the University of Mississippi, which inherently limits the quality and diversity of samples.^107,134 This is troubling on several accounts. First off, it is widely accepted that samples obtained from this source have more resemblance with marijuana from the 1980s than the wide variety and increased potency of cannabis products available on the commercial market today. In addition, restricting research to samples from just one source neglects to acknowledge both the biggest advantage and the greatest challenge associated with plant medicine: the idea that different strains produce different effects. Without access to the wide variety of cannabis products that are available to the consumer, the research becomes tenuous.

These are issues that researchers have faced for decades, but they become ever more relevant as both the medical and recreational use of cannabis are skyrocketing. At its core, the CSA provides a legal foundation for the government’s fight against drugs with a high potential for abuse. But what defines a “drug of abuse”, and why are some drugs viewed differently than others? To what extent does the policy on drugs like alcohol, tobacco, marijuana, and several prescription drug families reflect their true dangers? And how have these policies been modified and skewed in order to facilitate the regulating body’s political agenda? Here, the lines between government policy and scientific progress become blurred, especially as most academic research institutes rely heavily on funding provided by government agencies.¹³⁵ Really, it is a Catch-22 situation—as long as academic research on cannabinoids remains so heavily restricted, efforts to enforce the appropriate regulations on their consumption will remain futile.

4.3. Cannabis in Big Business

While federal regulations have not changed much since the 1970s, several states across the United States have loosened their restrictions on marijuana, creating a new legal cannabis market. In 1996, California passed Prop 215, the country’s first medical marijuana law, in an effort to provide relief to patients suffering from chronic illnesses. Since then, the movement has spread across the US in what has been called “medicine by popular vote”.^12,136 As of November 2021, medical marijuana is legal in 36 states across the United States, and 18 states as well as the district of Columbia have enacted legislation to regulate the nonmedical use of cannabis.¹³⁷ Consequently, the legal medical and recreational cannabis market has become a multibillion dollar industry and is expected to continue growing at a compound annual rate of 26% per year.¹³⁸

In fact, Big Marijuana has become so powerful that indirect competitors in Big Tobacco, Big Alcohol, and Big Pharma have recently announced deals with cannabis companies in response to the plethora of social and political campaigns against opioid, alcohol, and tobacco use.¹³⁹ In past years, the pharma giant Novartis, the alcohol firm Molson Coors Brewing, and several tobacco companies have joined forces with marijuana businesses in an effort to capitalize on this new movement.¹³⁹

The authors are grateful to Mr. Kevin Vargas for the design of TOC image. TOC was designed using resources from www.flaticon.com.