Endogenous vs Phytogenic vs Synthetic Cannabinoids

Three origins, one receptor system

About 600 million years of evolution produced a signalling system so fundamental that sea urchins have a version of it. The endocannabinoid system (ECS) wasn't discovered because researchers were curious about it in the abstract , it was found, mostly by accident, while scientists were trying to work out exactly where and how THC acted in mammalian tissue. That backstory matters, because it explains why we now talk about three quite distinct categories of cannabinoid as though they belong to one family. Mechanistically, they do. Chemically and legally, they're very different creatures.

The short version: endogenous cannabinoids are molecules your body synthesises itself; phytogenic cannabinoids are produced by plants; synthetic cannabinoids are made in a laboratory. All three can interact with the ECS, particularly at CB1 and CB2 receptors. That's roughly where the similarity ends.

Endogenous cannabinoids: made to order, used and destroyed fast

Your body produces endocannabinoids on demand , not stored in vesicles the way classical neurotransmitters are, but synthesised at the synapse when needed and broken down almost immediately after. The two best characterised endocannabinoids are anandamide (N-arachidonoylethanolamine, or AEA) and 2-arachidonoylglycerol (2-AG). Both are derived from arachidonic acid, a polyunsaturated fatty acid that sits within cell membranes.

Anandamide is a partial agonist at CB1 and CB2 receptors. 2-AG is a full agonist at both, and is generally present in the brain at concentrations orders of magnitude higher than anandamide, though it's also broken down more rapidly. Their degradative enzymes , FAAH for anandamide, MAGL for 2-AG; are themselves research targets, because inhibiting those enzymes allows endocannabinoid tone to increase without introducing exogenous compounds at all.

The on-demand synthesis model means endocannabinoids act primarily in a retrograde fashion at synapses: a postsynaptic neuron fires, releases endocannabinoids that travel backwards and bind to presynaptic CB1 receptors, modulating further neurotransmitter release. It's an elegant feedback loop, and quite unlike what happens with plant or synthetic cannabinoids flooding receptors from the outside.

Phytogenic cannabinoids: over 100 compounds from a single plant

Cannabis sativa is the best-known source of phytogenic cannabinoids, but it's not the only one, beta-caryophyllene, for instance, is a terpene found in a wide range of plants that acts as a CB2 agonist, which blurs the line between "cannabinoid" and "terpene" in ways that are still being argued about in the literature. For the purposes of this article, I'll focus on the canonical cannabis-derived compounds.

Phytogenic cannabinoids are synthesised in the trichomes of the cannabis plant, starting from cannabigerolic acid (CBGA), often called the "mother cannabinoid." Enzymatic and thermal processes convert CBGA into the acidic precursors, THCA, CBDA, and so on; which are then decarboxylated (by heat or light) into the neutral forms most people know: THC, CBD, CBN, CBC, CBG, CBDV, and dozens of others.

THC is the most pharmacologically potent at CB1, acting as a partial agonist with higher potency than anandamide, partly why exogenous THC can produce effects the endocannabinoid system itself doesn't. CBD's receptor pharmacology is genuinely more complicated; it has low affinity for CB1 and CB2 directly, and its documented mechanisms include antagonism at GPR55, modulation of TRPV1 channels, and indirect effects on endocannabinoid tone via FAAH inhibition. The "it doesn't bind the receptors" line you sometimes see is an oversimplification.

I'll admit I got this wrong for years, I kept framing CBD as essentially receptor-inactive, which the more recent binding studies make clear isn't quite the full picture.

Worth noting: minor cannabinoids like Delta-8-THC, Delta-10-THC, THCP, and HHC occupy a regulatory grey zone in many countries. In Australia, most THC analogues are captured under the Poisons Standard regardless of their specific isomeric form. Anyone marketing products containing these compounds should understand that the Therapeutic Goods Administration's scheduling enforcement does not distinguish between structural analogues on the basis of novelty; if it has psychoactive cannabinoid activity, it is almost certainly scheduled.

Synthetic cannabinoids: precision tools and serious hazards

Synthetic cannabinoids were, initially, a research innovation. Laboratories developed compounds like WIN 55,212-2 and CP-47,497 as molecular tools to characterise the ECS, to map receptor distributions and understand binding kinetics. The pharmaceutical industry followed, producing compounds with specific receptor profiles for investigational use. That research lineage is legitimate and ongoing.

But the term "synthetic cannabinoid" now spans an enormous range. On one end: carefully characterised pharmaceutical-grade molecules produced under Good Manufacturing Practice conditions, some of which appear on the Australian Register of Therapeutic Goods (ARTG) and are accessible via the Special Access Scheme or through an Authorised Prescriber. On the other end: the "designer drug" class, sold under names like Spice, K2, and dozens of others; which are full agonists at CB1 with far higher potency than THC, unpredictable metabolite profiles, and a significant clinical risk record.

The distinction is real and matters a lot. A synthetic cannabinoid developed by a pharmaceutical company, characterised in peer-reviewed literature, and registered with the TGA is a fundamentally different entity from an unscheduled analogue sprayed onto plant matter and sold at a servo. Lumping them together because both were made in a lab does nobody any favours.

In Australia, most novel synthetic cannabinoids are captured as Schedule 9 (Prohibited Substances) under the Poisons Standard, or become so as new analogues are specifically added. Supplying unapproved synthetic cannabinoids is a criminal matter under state and territory drug laws as well as Commonwealth legislation.

How the three classes interact differently with CB1 and CB2

Receptor pharmacology is where the three classes diverge most sharply. Endocannabinoids are partial agonists, they bind and activate, but the signalling ceiling is lower than a full agonist would produce. They also act transiently, degraded within seconds to minutes. Phytogenic cannabinoids like THC are also partial agonists at CB1, but they resist rapid degradation, persist in tissue, and can accumulate in lipid-rich environments given their lipophilicity. Synthetic cannabinoids from the designer class are typically full agonists, with binding affinities that can exceed THC by one to two orders of magnitude.

That difference in intrinsic efficacy, partial vs. full agonism; is clinically significant. Full agonism at CB1 is associated with a substantially higher risk of adverse events: cardiovascular effects, acute psychosis, seizures. The blotter of safety data that exists for cannabis over millennia of use does not extend to these synthetic full agonists.

CB2 pharmacology is a slightly different story. Because CB2 is expressed predominantly in peripheral immune tissue rather than the CNS, full agonism there carries a different risk profile, which is part of why selective CB2 agonists have attracted pharmaceutical interest without the same psychoactivity concerns.

Classification in Australian law

Under Australia's Poisons Standard (the document that underpins scheduling decisions nationally), cannabinoids sit across multiple schedules depending on the specific compound and intended use. CBD in preparations meeting specified criteria sits at Schedule 4. THC-containing medicines are generally Schedule 8 controlled drugs. Psilocybin and most novel synthetic cannabinoids are Schedule 9 prohibited. The TGA's guidance on accessing unapproved cannabis medicines via the SAS or Authorised Prescriber pathway is the appropriate starting point for anyone in the clinical space, the TGA website (tga.gov.au) publishes current access data quarterly.

Honestly, the scheduling framework is more coherent than it sometimes gets credit for. It's not perfect, and the lag between novel compound emergence and formal scheduling can create real grey zones, but the underlying logic, risk-proportionate access tiers; is sound.

Why the classification still matters to the science

Between swim sessions last summer I spent a week going back through early ECS mapping papers, the Matsuda et al. 1990 CB1 cloning paper, the Munro et al. 1993 CB2 work, and what struck me is how much of the foundational pharmacology was done using synthetic probes before plant cannabinoids were well-characterised. The three categories aren't just a regulatory taxonomy; they reflect genuinely different scientific histories.

Understanding that endocannabinoids are transient, phytogenic cannabinoids are persistent and lipophilic, and synthetic cannabinoids span a vast efficacy spectrum; that's not just trivia. It shapes how researchers design studies, how regulators think about risk, and how the broader cannabinoid science conversation should be framed. The ECS didn't evolve to receive plant chemicals. It evolved to receive the body's own signals. Everything else is, in a sense, a visitor at a door the body built for itself.

Sources

• Endocannabinoid system: An overview of its potential in current medical practice, National Center for Biotechnology Information (NCBI/NIH)
• Medicinal cannabis guidance documents, Therapeutic Goods Administration (TGA)
• Synthetic cannabinoids drug facts; Alcohol and Drug Foundation (ADF)
• Cannabinoid receptor pharmacology, Annual Review of Pharmacology via NCBI/NIH

, Elise Tran, Science writer, cannabinoids & the ECS