Interpreting Your Potency Results Part II

Calculating ‘Total’ Cannabinoids - The THC potency at the time of testing is NOT what the potency will be at the time of consumption.

When reviewing your product’s potency results on the Lightscale Labs Certificate of Analysis (COA), you’ll notice there’s more than one value for THC. You’ve got Δ9-THC, THCA, and then a big, bold number called ‘Total THC.’ Each of these numbers is different, and each is important.

A Certificate of Analysis from Lightscale Labs displaying the average levels of various cannabinoids contained in a batch of cannabis flower.

Here’s the COA for a batch of cannabis flower. Let’s evaluate how we arrived at each of those potencies.

By Oregon state law, “Total THC” must measure psychoactive THC (current or future) in all its different and various forms. (As of May 2021, Δ8-THC is not factored in to Total THC, but that will likely change very soon.) Most cannabinoids exist in an acidic and non-acidic form, such as THCA (non- psychoactive) and Δ9-THC (psychoactive).

Sure, the lab can measure the amount of each form of THC in the flower and add them together… but this gets tricky, because the THCA molecule and the Δ9-THC weigh different amounts. Potency is a description of what percentage of the product, by weight, is comprised of each particular kind of molecule, so this small discrepancy in molecular weight really matters!

What differentiates a THCA molecule from a Δ9-THC is a carbon, 2 oxygens, & a hydrogen atom, otherwise knowns as a Carboxyl Group.

When the vape cartridge is consumed, heat from the vape pen will cause many of the THCA molecules to lose a cluster of atoms known as a ‘carboxyl group.’ (Don’t freak out, it's just a carbon atom, two oxygens, and a hydrogen.) This process is called ‘decarboxylation’ and is what transforms THCA into Δ9-THC.

The carboxyl group accounts for about 12.3% of the weight of each molecule of THCA. So as soon as the group detaches and floats away, (it now lives as CO2 in the air, so you’re welcome, trees) the resulting Δ9-THC weighs 87.7% as much as it originally did.

What further complicates things is the fact that, legally, the product must be labeled with what the potency WILL BE at the time of consumption, which is not the same as the potency at the time of testing.

What currently exists in your product as a heavier THCA molecule will likely be inhaled by the consumer as a lighter Δ9-THC molecule. So, to know the true, at-the-time-of-inhalation potency, we need to adjust the weight of any THCA that shows up in the test results. Only then can we add it to the level of Δ9-THC level that exists naturally in the product. Together, the current weight of Δ9-THC plus the future weight of THCA that exists in 1 gram of product gives us the ‘Total THC’ potency.

(Many other cannabinoids also have acidic and neutral forms. Luckily, when CBDA is decarboxylated, the resulting CBD molecule also weighs 87% of its former self. Therefore, the same calculations used in this article for THC can be utilized to calculate Total CBD.)

In other words, we need to know what all that THCA will weigh after it’s been decarboxylated and becomes Δ9-THC.

An Example

Let’s say we test some (unbelievably potent) buds, and find out that each 1 gram of flower contains:

100mg of Δ9-THC (or 10% THC)

342mg of THCA (or 34.2% THCA)

100 mg of THC per 1 gram of flower means that 10% of every 1-gram nug is composed of THC molecules.

We know that when THCA is decarboxylated and becomes Δ9-THC, it will weigh 87.7% as much as it currently does. Therefore, we need to use the equation:

THCA × 0.877 = Future Potency of Δ9-THC

Heat will cause a molecule of THCA to separate into its constituent parts: 1 molecule of CO2 & 1 molecule of Δ9-THC.

Using our analytical results for this particular product, we get:

342mg THCA (now) × 0.877 = 300mg Δ9-THC (future)

Add that to the 100mg of Δ9-THC that already exists in our flower:

100mg Δ9-THC (now) + 300mg Δ9-THC (future) =

400mg Δ9-THC (per 1 gram of flower)

Which could also be written as:

Total THC Potency = 40%

Once decarboxylated THCA becomes Δ9-THC, it is added to the ‘Total THC’ potency amount.

Be In the Know

Understandably, we often get the question from clients, “why do I need to know all this math? Doesn’t the lab calculate all this ‘Total THC’ stuff for me?” The answer to that question depends on what state you live in, and what lab you use for testing. In Oregon, the THC level tracked by the state (aka listed in METRC) is required to be the fully-calculated Total THC potency. Some states have similar rules.

Across the country, however, there are few laws about how labs have to report information on their Certificates of Analysis, which is what many dispensaries use to determine whether or not they will buy a batch of cannabis product. There are plenty of COAs that list ‘Total THC’ as simply “THCA% + Δ9-THC%.” It’s not difficult to see why: forgetting to adjust for the weight lost during decarboxylation artificially inflates the perceived THC potency of a product. Unfortunately, reporting Total THC this way is at best misleading, and at worst, completely inaccurate.

Take the batch of flower from our example math problem above. Without adjusting for decarboxylation, you would simply arrive at the wrong ‘Total THC’ level.

When reading a Certificate of Analysis, always look to see that the THCA potency has been multiplied by that magic number, 0.877, before being added into the Total THC. Furthermore, make sure the “Total THC” level written on the COA matches what is being reported to the state (in METRC, or whatever Cannabis Tracking System your state uses.) Perhaps one day all analytical test results will be reported clearly and transparently. Until then, it is important to understand where your potency numbers are coming from.

Up Next: How Well Does the Average Potency Really Represent the Batch?