Cannabis potency: Why you shouldn't trust the label

A broad survey of Colorado dispensaries found that nearly half of all cannabis flower products are mislabeled. The THC potency listed on the package often doesn’t match what’s actually inside.

Most of the inaccurate labels overstate the amount of THC – the psychoactive compound in cannabis. By contrast, testers found that almost all of the concentrates examined – including oils and waxes – were labeled correctly. In fact, 96 percent fell within an acceptable margin of error.

These findings come from the first large-scale audit of potency labels in a legal cannabis market. The researchers provide a rare look at today’s cannabis potency, highlighting where testing is reliable and where it needs improvement.

THC labels are often inaccurate

Study senior author Cinnamon Bidwell is an associate professor of psychology and neuroscience at the University of Colorado Boulder and co-director of the Center for Health and Neuroscience, Genes, and Environment (CU Change).

“Cannabis use has complex and wide-ranging effects, and we are working hard to better understand them,” said Bidwell. “While that research plays out, we should, at the very least, be providing accurate information about the amount of THC in these products.”

The Institute of Cannabis Research – Colorado’s official cannabis research institute – funded the project, which researchers carried out with MedPharm Research, LLC, a licensed testing lab, manufacturer, and retailer.

“We want to instill and foster trust in products, and the only way to do that is to continually evaluate and correct any issues that might be discovered,” said Duncan Mackie, director of pharmacology at MedPharm and a co-author of the paper.

Testing reveals true cannabis potency

Because federal regulations prohibit university scientists from purchasing or handling commercially available cannabis, the team collaborated with MedPharm to collect samples.

A “secret shopper” visited 52 dispensaries across 19 Colorado counties. They purchased 277 products: 178 flower items – including loose buds and pre-rolled joints – and 99 smokable concentrates, ranging from distilled oils to Moroccan hash and waxy “sugar.” Edibles were not part of this phase of the study.

The shopper photographed each label and anonymized every sample with a number. MedPharm chemists, blind to the labeling information, then tested each product.

Flower samples averaged 21 percent THC; concentrates averaged 71 percent, with some as high as 84 percent. For perspective, marijuana in the 1980s typically contained about 8 percent THC.

Where THC labels fall short

Colorado considers a cannabis label accurate if the product’s THC content is within 15 percent (higher or lower) of the printed value. Among flower products, 44 percent missed that mark. Of those, 54 items overstated THC levels, while 23 contained more THC than advertised.

Though the average discrepancy was modest – about two percentage points – some errors were large. One sample labeled 24 percent THC, for instance, tested at only 16 percent.

Concentrates fared much better: only four samples fell outside the acceptable range. “When it comes to concentrates, Colorado gets a good grade for labeling accuracy, but there are some real issues with flower,” Bidwell said.

Previous work in other states suggests some third-party testing labs inflate potency results, possibly to satisfy businesses seeking stronger-sounding products.

Yet concentrates, which are homogeneous oils, are easier to measure than the heterogeneous structure of plant material.

This difference offers another explanation for why flower labels run off-target. Standardizing plant sampling methods could reduce label discrepancies, the authors note.

Labels miss key compounds

Colorado requires labels to list cannabidiol (CBD) content, and 80 to 85 percent of products complied. However, only 16 percent included information on other cannabinoids, such as cannabigerol (CBG) and cannabigerolic acid (CBGA).

Interestingly, the tests found greater quantities of CBG and CBGA – compounds with potential anti-inflammatory and anti-anxiety effects – than CBD across product types. Yet labels rarely show those figures.

“Focusing on THC on the label can actually do a disservice for consumers, because it creates an environment in which people buy based solely on THC content,” Bidwell said. “Our data suggests that multiple other cannabinoids should also be reported there.”

Edibles will be examined next

Backed by additional funding from the Institute of Cannabis Research, the team plans to extend its label audit to include edibles and other product categories.

As more states legalize cannabis for medical and recreational use, accurate labeling will become increasingly important for patient safety, informed recreational use, and public trust.

“We all want the same thing: a strong, successful industry that regulators can feel good about, businesses can thrive in, and customers can trust,” Mackie concluded.

The study is published in the journal Scientific Reports.

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