What Is THCA? How It Turns Into THC

THCA, short for delta-9-tetrahydrocannabinolic acid, is the acidic precursor of THC. The plant makes it from CBGA with an enzyme called THCA synthase and stores it in the glandular trichomes on its flowers and leaves, where it can represent up to 90% of the total THC (Moreno-Sanz, Cannabis and Cannabinoid Research, 2016).

THC itself is scarce in the living plant. A 2016 decarboxylation study notes that THC, CBD and CBG do not occur in significant concentrations in cannabis, which mainly makes their acid forms, THCA, CBDA and CBGA (Wang and colleagues, Cannabis and Cannabinoid Research, 2016). Friedhelm Korte of the University of Bonn first identified the acid as a major component of hashish in 1965 (Moreno-Sanz 2016).

Unlike THC, THCA does not produce psychoactive effects in humans, and it does not appear to convert into THC inside the body (Moreno-Sanz 2016). Because heat does the converting, much of the THC people take in is formed when cannabis is smoked, vaped or cooked.

Health Canada makes the same point in its guidance to producers: when a product contains THCA and the way it is consumed will not convert it to THC, as with oils taken by mouth, producers may want to add label information to help people dose (Health Canada labelling guide).

The reaction is called decarboxylation: THCA loses its carboxylic acid group and becomes THC. It happens quickly with the heat of smoking, vaping or baking and slowly during storage (Moreno-Sanz 2016), and light can drive it too (Wang 2016).

Time and temperature both matter. In the Wang study, which heated dried cannabis extract in a vacuum oven, THCA was almost entirely converted after 30 minutes at 110°C, 9 minutes at 130°C and 6 minutes at 145°C, while below 100°C the reaction was still incomplete after 60 minutes. Those are lab conditions, not a kitchen oven or a joint.

Smoking is less efficient. Studies summarized in the 2016 review found that between about 30% and 70% of THCA ends up as THC, depending on the conditions (Moreno-Sanz 2016).

THC can also break down further into CBN with heat, oxidation and light (Moreno-Sanz 2016), which is one reason storage matters. See what CBN is and how it differs from CBD and how to store weed to keep it fresh.

Legal cannabis labels in Canada must show Total THC on the front of the package (Health Canada). Health Canada's labelling guide describes that figure as the THC a product could yield, "taking into account the potential to convert THCA into THC". In other words, THCA counts toward Total THC.

Producers must test each lot or batch for both THCA and THC, and limits such as 10 mg of THC per container of edible cannabis are also calculated with THCA's potential to become THC included (Health Canada).

To read the number: according to Health Canada's example, a 30-gram package labelled "Total THC 180 mg/g" contains 5,400 mg of THC in total, and 180 mg/g is the same as 18%. If a menu lists THCA instead, remember that heat turns it into THC, so the figure describes THC potential, not a milder product.

THCA is treated as cannabis. Schedule 1 of the Cannabis Act covers every part of the cannabis plant, including its phytocannabinoids, plus molecules identical to a phytocannabinoid however they were obtained (Health Canada), and Health Canada says all phytocannabinoids are regulated under the Act (Health Canada).

So Canada has no separate category for THCA flower or THCA concentrates: they follow the same rules as other cannabis, and their THCA counts toward Total THC and toward THC limits.

Very little is known about what THCA does in people. As of the 2016 review, most findings came from cell studies, only 1 animal study had been published, and whether THCA binds to the CB1 receptor that THC acts on was still disputed (Moreno-Sanz 2016). Reports of people using unheated cannabis preparations are anecdotes, not clinical evidence.

None of this shows that THCA treats or prevents anything. If you are thinking about THCA for a health reason, talk to a doctor or pharmacist.

Most of the THC potential in dried flower is still THCA until it is heated, which is why Total THC is the number to compare. GasDank delivers same day across Toronto and the GTA, usually within 1 to 2 hours, and ships across Canada by mail order. Browse all flower or concentrates; the menu carries lab-tested products. Customers must be 19 or older (21 in Quebec), with ID checked at the door.