In 1964, the great chemist Raphael Mechoulam first published "Isolation, structure and partial synthesis of an active constituent of hashish" in the Journal of the American Chemical Society ⁽¹⁾. Since then, the world has learned that the active component of Cannabis is a chemical called tetrahydrocannabinol or THC. In actuality, there are a handful of different isomers of tetrahydrocannabinol that we generally refer to as THC. The most prominent one Mechoulam found in hashish was a compound called Δ^⁹-tetrahydrocannabinol. Once Mechoulam and others began looking for active compounds in fresh and cured cannabis, they actually found the biological precursors to them in the form of acids. The biological precursor of THC is Δ^⁹-tetrahydrocannabinolic acid or THCA. Similarly, CBG, CBD, THCV, CBDV and other cannabinoids all have conjugate acid forms as the principal precursors we find in fresh and cured cannabis in the markets today.

A carboxylic acid group. The R represents any number of potential molecules.

The term acid in this context refers to a carboxylic acid group, a simple -COOH on the side of the molecule (see image above). With a bit of energy, -COOH, carboxylic acid groups spontaneously leave the molecule in a process called decarboxylation (Fig. 1).

Figure 1: Decarboxylation of THCA by heat.

Carboxylic acid groups are common in biochemistry and many natural plant compounds are synthesized with a -COOH group. This is an evolutionary remnant due to how plant enzymes synthesize complex molecules like resins, terpenes, cannabinoids, polyphenols, and other phytochemicals ⁽²⁾. The difference between THC and its acid form is subtle, but makes a great difference in our pharmacognosy of cannabis medicinal compounds. Both THCA and THC have similar binding affinities to endocannabinoid receptors and have similar pharmacokinetics. However, unlike THC, THCA does not pass the blood-brain barrier and thus is not regarded as a psychoactive compound. With a little heat, THCA will spontaneously lose its carboxylic acid group (-COOH) as carbon dioxide, CO₂. The same principal applies to the decarboxylation of other cannabinoid acids. This is why long before THC and cannabinoids were ever discovered, heating cannabis was always part of the medicinal herbal lore. Cannabis requires “activation.” In other words, it requires the heat of a flame (from smoking) or the heat of a burner (from cooking) before ingestion. Though THCA is not regarded as being “active” or psychotropic, it almost certainly possesses therapeutic properties and has been studied as such; For example, it is known to possess significant anti-inflammatory properties ⁽³⁾.

The subtle, structural differences between THC and THCA yield dramatic differences in their therapeutic, metabolic and pharmacokinetic properties. As a result, subtle differences in the analytical methodology, instrumentation, and reporting used to assay cannabis potency have a large effect on the quality of information coming from these analyses. If we are to test a batch of cured cannabis and assay cannabinoid potency as a measure of quality, then we can make a small calculation to estimate the total available THC from a measure of THCA in the plant.

Editor’s Note: The formula that can be used to calculate total THC potency is available here.

But if we apply our technical skills to assay cannabinoid infused products for ingestion, the specific amounts of actual THCA and THC present in the sample will govern the way the product performs. For example, in formulated cannabis-infused edible products, the “felt effect” will be governed by the amount of THC. While the presence of THCA in the edible product can be considered therapeutic, it does not contribute to the intoxicating properties. So, accurate analytical resolution of THC and THCA is critical when evaluating ingestible cannabinoid products.

How cannabinoids change with heat and/or time is a huge part of the research behind how cannabis works in the body and why it seems to be so crucial for healthy body function. The endocannabinoid system can use different cannabinoids for different issues and needs. With so many more doctors and researchers focused on this topic, it will only be a matter of time before we fully understand how the body uses all the different chemicals.

1. Gaoni Y & Mechoulam R. (1664) Isolation, Structure, and Partial Synthesis of an Active Constituent of Hashish. J. Am. Chem. Soc., 1964, 86 (8), pp 1646–1647
2. Geissman TA. The Biosynthesis of Phenolic Plant Products. and Nicholas HJ. The Biogenesis of Terpenes in Plants. in, Biogenesis of Natural Compounds. Bernfeld P, (Ed). 1963 Pergamon Press.
3. Ruhaak LR, et al. (2011), Evaluation of the cyclooxygenase inhibiting effects of six major cannabinoids isolated from Cannabis sativa. Biological and Pharmaceutical Bulletin, 34 (5): 774–8

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