A Primer: Cannabis Potency Testing and Labeling Issues

Or, Why does 46% THC Weed Look so Terrible?

As a medical cannabis consumer, I need to track information about the cannabis I consume so I can track whether or not it is effective. At one point, I felt that cannabis testing could be an ally in discovering what it was in the strains that were helping me. Until I started to learn more about cannabis testing in detail.

Even in the best case, the THC potency listed on a container may not reflect what’s in the package.

Let’s talk about how cannabis testing generally works: and how it goes wrong.

The exact cannabis you buy from the dispensary isn’t tested – the methods used to test cannabis destroys it in the process. Instead, a representative sample of material is taken for testing. Accuracy in cannabis potency testing depends on precision across many steps: sampling, homogenization, and the testing itself must be correct in order for the test results to accurately represent the cannabis or cannabis product. Most cannabis lab employees I’ve engaged with are passionate about both the science and the plant and take every precaution necessary to ensure the steps are followed to a tee.

But there are those that are more than willing to use the power of the lab coat to lie to turn a quick dollar. And for those bad actor labs wanting to engage in artificially inflating THC potency to get their farmer clients more money – there are many opportunities to do so. 


Sampling is the act of taking a representative sample of cannabis to be tested from a batch. 

Batches can be as large as 50 pounds (sometimes more), which means it’s more important that care be taken in ensuring the representative sample is performed appropriately. Batches of flower are grouped by strain, and batch size is the major dictator of testing costs. This means that testing costs are a higher burden on smaller, craft farms. 

As little as .5% of material can be used to sample from these batches, so the importance of that material as being ‘representative’ of that batch as a whole is paramount. Sampling methods must be precise and consistent in order to ensure the sample is as statistically representative of the batch as possible. Specific information and rigorous sampling training is required to ensure consistent samples across a single lab – much less across all of the labs of a state. 

Only taking the most beautiful looking buds isn’t the only way that sample can be manipulated. In some states, ‘kiefing’ the batch is legal – or, people are allowed to re-introduce kief from a strain back into a batch before testing. 

Often there is also a chain of custody issue – meaning that the batches for testing are presented to the sampler, without any confirmation that it’s truly the product destined for shelves.  Swapping a sample is exceptionally easy in testing environments without off-the-shelf testing or a state-run reference lab.


Once the sample is taken, it needs to be homogenized. Homogenization is basically making cannabis into a fine powder that will be even more representative of that cannabis sample. If this step isn’t performed correctly, it can skew the results.

I have heard of and seen many different homogenization methods, and labs often pride themselves on their homogenization practices being as precise as possible. I’ve had some labs go into extensive detail about how THC crystals can stick to each other, necessitating things like cryogenic homogenizers. 

Any ‘Cheats’ that happen during the homogenization stage would carry a similar impact a lot like those in the sampling stage as homogenization is an extension of sampling. Without everyone using industry-wide, agreed upon standards, homogenization processes can introduce a lot of variability: intentionally or not.

The Science!

Once homogenized, the sample is weighed and then diluted through a couple of solvent preparations and some spins on a centrifuge before being handed over to the machine that will interpret what it might contain by comparing it to samples it ‘knows.’  High Performance Liquid Chromatography (HPLC) is the current gold standard of potency testing, and in order for it to work, it requires careful and precise calibration using a cannabis reference standard.

Cannabis Reference Standards 

A cannabis reference standard is material that can be used to calibrate equipment that is testing for cannabinoid potency. 

The reference standard presents additional complications. For some substances, it’s easy to acquire high quality reference standard material. You might have read the amusing story about the $761 peanut butter that is used by the National Institute of Standards and Technology (NIST) so that food labs have a way to calibrate their gas chromatographs. In the case of peanut butter – no problem. But in the case of cannabis, a federally illegal substance, the only labs that can access the highest quality of standard would require a DEA license. As you can imagine, many cannabis labs have issues acquiring this license due to being involved in a federally illegal activity.

The cannabis reference standard is an area labs often cite as an issue in areas where cheating is suspected. Since the reference standard is used to calibrate overall measurements for the whole machine, it’s an effective way for bad actor labs to intentionally use a high-reporting, low-quality standard while still maintaining that their numbers are accurate.  

To go back to the peanut butter example, it would be like the food lab choosing to use some random store brand peanut butter to test instead of NIST’s carefully controlled sample.


Once the data is analyzed, the THC potency can be extracted by using the formula % Total THC = % THC + (% THCA x 0.877). The potency, along with pesticide, heavy metal, and microbial testing information, is entered into the LIMS and is then is often either entered into or interfaced with a state’s seed to sale/ testing system (if they have one). 

Some bad actor labs can use some ‘magical math’ to make potency just a bit better for their clients. Moisture percentage can impact the THC potency of a sample. Different ‘loss on drying’ calculations can also slightly impact the THC potency. The most impactful ‘math trick’ is less a trick of math and one of being imprecise in weights: if the incorrect sample weight is entered it can radically change the THC percentage (and would be an easy number to alter as most LIMS allow manual entry for that value).


Many labeling and testing laws allow for an error threshold of total potency (meaning that the label is allowed to be out of synch with contents by a particular amount.), These laws (of course) vary state to stateColorado, for instance, allows misstatement of potency by up to 15%!

That’s not the only time inflation may legally be allowed on the label! 

In some states cannabis is prepackaged and sold with the appropriate labels, and in others, dispensaries create the labels and apply them to containers of flower as sold.  Sometimes, in such states, a “tolerance” is allowed between the tested percentage and the percentage as advertised – of up to 10%.  When you add those two together, it represents a 20% allowed overstatement of the tested product!


Cannabis potency testing is an exciting new science with a lot of potential to support medical and recreational users. Sampling, homogenization, and all of the science behind cannabis testing could be an amazing ally of consumer safety advocates.  However, because of the precision demanded and the lack of meaningful regulations and oversight, this new science presents many opportunities for bad actors to cheat the numbers for profit.