Many dispensaries are vending their products with a number termed “Total THC”. This is a fuzzy value which represents a combination of lab-measured numbers which implies greater potency and usually bumps the percentage numbers of flower into the attractive >20% range. Those who are not aware of the intricacies of THC often buy their medicine based solely on this number, believing this to be the only, or at least primary, indicator of quality.

“THC”, in general parlance, is a catch-all label for an extremely complex molecule. As the cannabis plant grows, it produces fatty acids, tetrahydrocannabinolic acid, or “THCa”. This form is not psychoactive, but does have medicinal value, including anti-emetic and anti-inflammatory properties. After the flower is removed from the plant and begins curing, or with the direct application of heat, THCa begins to decarboxylate into delta-9 THC, the psychoactive molecule tetrahydrocannibinol. Delta-9 is readily usable by humans, with its own medicinal values similar but separate from THCa.

So what then is the “Total THC” reported by some labs and dispensaries? This number is a simply a combination of THCa and THC. Specifically, THCa is directly measured through high-pressure light chromatography (HPLC; gas chromatography, GC, does not directly measure THCa, but derives it based on the delta-9 value). Then the decarboxylated value, delta-9, is read and added to the base value, giving the composite “Total THC”. The question remains, then, what benefit does this reading give to lab results?

Simply, this combination of readings gives a high THC number, which less informed patients can then take as indicating a high level of psychoactivity, or otherwise judge the medicine of being higher value. However, “Total THC” does not necessarily indicate anything of scientific value beyond a high number to take to market.

To understand the medicinal value, one needs to know the specific readings. For example, Concentrate A contains 80.84% THCa and 3.95% delta-9 measured with an HPLC. “Total THC” for Concentrate A equals 84.79%. A dispensary could honestly round that percentage, and label this as 85% Total THC. The problem, then, is that when dabbed the THCa decarboxylates so actually only contains 67% delta-9 ( 80.84/1.28 + 3.95 = 67.11 ).

Now, when one uses Concentrate A to prepare an edible, this difference can become even more evident. The body processes both THCa and delta-9, but converts each molecule differently; delta-9 will be psychoactive, while THCa will not be psychoactive. If the edible is cooked, most of the THCa will decarboxylate into delta-9 creating a highly psychoactive product. If the edible is icing, for instance, and not cooked, then the THCa will stay as it is, and the finished product will have low psychoactivity. “Total THC” without the further testing of individual molecules, gives little guidance to the producer.

There is a tremendous amount of knowledge that is only now coming to light about the effects and structures of Cannabis. What is known and what is assumed to be true about medical marijuana will be challenged, quantified, and examined scientifically in the coming years. Patients, doctors, and everyone working in the medical marijuana field will be best served by accuracy and honest assessment to the best of what science can tell, even as that knowledge is in a state of flux.

–Betsy Gribble, Information Services

Sequoia Analytical Labs