How strong is your weed? Study shows labels often misrepresent potency

Nearly half of cannabis flower products are inaccurately labeled when it comes to potency, with most showing they contain more THC than they really do. Meanwhile, labels on cannabis concentrates like oils and waxes tend to be accurate, with 96% shown to match what’s inside.

That’s the takeaway from a sweeping new analysis of products sold at dispensaries across Colorado—the first state to legalize recreational marijuana. The study, published this month in the journal Scientific Reports, is the first comprehensive label audit of legal market cannabis to date, providing insight into just how strong cannabis has become, what the burgeoning industry is getting right in terms of testing and labeling and where it can improve.

“Cannabis use has complex and wide-ranging effects, and we are working hard to better understand them,” said senior author Cinnamon Bidwell, associate professor of psychology and neuroscience at CU Boulder and co-director of the Center for Health and Neuroscience, Genes and Environment (CU Change). “While that research plays out, we should, at the very least, be providing accurate information about the amount of THC in these products.”

The study was conducted in collaboration with MedPharm Research, LLC, a licensed cannabis testing facility, 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 on the paper.

Stronger weed, problematic labels

Under federal law, university scientists are not allowed to purchase or handle legal market cannabis for research, so collaborating with industry is critical, said first author Gregory Giordano, professional research assistant in the Department of Psychology and Neuroscience.

For the study, a secret shopper from MedPharm traveled the state to obtain 277 products from 52 dispensaries across 19 counties.

The sampling included 178 flower products (loose flower and pre-rolled joints) and 99 smokable concentrates—everything from vials of distilled liquids to balls of Moroccan hash and gobs of waxy “sugar.” No edibles were included in this phase of the study.

The shopper shared label photos with Bidwell’s team. Then the samples, marked only with a number, were tested by MedPharm chemists who hadn’t seen the labels.

Data analysis showed that flower products contained on average about 21% THC, or tetrahydrocannabinol—the main psychoactive ingredient in cannabis. Concentrates contained 71% THC on average, with some containing as much as 84%.

In the 1980s, the typical THC content in marijuana was around 8%.

“THC content has increased significantly, and we know that greater THC exposure is likely associated with greater risks, including the risk of cannabis use disorder and some mental health issues,” notes Bidwell.

Products were considered “accurately labeled” if they contained within 15% of the THC amount shown on the label—the same threshold the state uses.

About 44% of flower products failed to meet that standard, with 54 of those products inflating their THC content on the label and 23 containing more THC than the label indicated.

Either is concerning, the researchers say.

For those using cannabis medically, adequate dosing can be critical. For those using cannabis recreationally, taking more than expected can be dangerous.

Some discrepancies were large—one flower product was labeled as having 24% THC but had only 16%. But on average, the difference between labeled and observed THC was about 2%.

Only four concentrate products were labeled inaccurately.

“When it comes to concentrates, I would say Colorado gets a good grade for labeling accuracy, but there are some real issues with flowers,” said Bidwell.

Previous research in other states has shown that third-party testing labs often inflate THC potency, possibly to gain the business of marketers wanting to attract consumers seeking stronger products.

However, there are other potential explanations for the discrepancy: Concentrates are often made from homogeneous oils that are easier to analyze, whereas plants are inherently heterogeneous and harder to test.

Small changes in testing protocols could reduce mislabeling, the researchers said.

Beyond THC and CBD

The study also looked at several other cannabinoids (active compounds found in the Cannabis sativa plant), including cannabidiol (CBD), cannabigerol (CBG), and cannabigerolic acid (CBGA). Colorado law requires that companies put CBD levels on the label, a standard that 80% to 85% of products met.

But only 16% of products featured any information at all about other lesser-known cannabinoids.

Notably, CBG and CBGA, which have been associated with anti-inflammatory and anti-anxiety properties, were more abundant than CBD in products across categories.

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

What’s next? Bidwell and Mackie plan to look at—among other things—labels for cannabis edibles.

As more states legalize the plant for medicinal and recreational uses, they hope their research can inform how states regulate it.

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