How strong are your herbs, really? Scientists say labels are often misleading

These findings come from a large-scale analysis of cannabis products purchased from licensed dispensaries throughout Colorado, the first state to legalize recreational marijuana. Published in Scientific reportsThe study represents the most detailed review to date of the status of cannabis brands in the legal market. It offers new insight into how effective cannabis is today, what testing and labeling practices work, and where the system is still deficient.

“Cannabis use has complex and wide-ranging effects, and we are working hard to better understand them,” said lead author Cinnamon Bidwell, assistant professor of psychology and neuroscience at the University of Colorado Boulder and co-director of the Center for Health, Neuroscience, Genes, and Environment (CU Change). “While conducting this research, we must, at the very least, provide accurate information about the amount of THC in these products.”

The project was funded by the Cannabis Research Institute, Colorado’s official research institute, and conducted in partnership with MedPharm Research, LLC, a licensed testing facility, manufacturer, and retailer.

“We want to instill and enhance confidence in products, and the only way to do that is to continually evaluate and correct any issues that may be discovered,” said Duncan Mackey, director of pharmacology at MedPharm and co-author of the paper.

How the research was conducted

Because federal law prohibits university scientists from purchasing or dealing with cannabis directly from the legal market, industry collaboration was essential, explained first author Gregory Giordano, a professional research assistant in the Department of Psychology and Neuroscience at the University of Colorado Boulder.

MedPharm’s “secret shopper” traveled throughout the state collecting 277 cannabis products from 52 dispensaries in 19 counties. The sample set included 178 flower products (loose flower and pre-rolled joints) and 99 smokable concentrates ranging from distilled liquids to Moroccan hashish and waxy “sugar.” Edible materials were not part of this phase of the research.

Images of each sign were provided to the Bidwell team. The samples, identified by numbers only, were then tested by MedPharm chemists who had not seen the original labels to ensure objectivity.

What the tests revealed

On average, hemp flower products contain about 21% tetrahydrocannabinol (THC), or tetrahydrocannabinol, the main psychoactive compound in marijuana. Concentrates averaged 71% THC, with some reaching as high as 84%. By comparison, marijuana in the 1980s typically contained about 8% tetrahydrocannabinol (THC).

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

Products were considered “micro-labeled” if they contained 15% of the amount of tetrahydrocannabinol (THC) shown on the label — the same limit used by the state.

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

Both are troubling, researchers say.

For those who use cannabis medically, adequate doses can be crucial. For those who use cannabis recreationally, taking a larger amount than expected can be dangerous.

Some of the discrepancies were significant – one flower product was labeled as containing 24% THC but contained only 16%. But on average, the difference between labeled and observed THC was about 2%.

Only four concentrated products were inaccurately labeled.

“When it comes to concentrates, I would say Colorado gets a good score for labeling accuracy, but there are some real issues with the flower,” Bidwill said.

Why efficacy labels can vary

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

However, there are other possible explanations for this discrepancy: concentrates are often made from homogeneous oils that are easy to analyze, while botanicals are inherently heterogeneous and difficult to test.

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

Beyond THC: Other cannabinoids are also important

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

But only 16% of products contain any information at all about other, less well-known cannabinoids.

Notably, CBG and CBGA, which are 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 harm consumers, because it creates an environment where people buy based solely on the THC content,” Bidwill said. “Our data suggest that many other cannabinoids should also be reported there.”

Looking to the future: Improving cannabis labeling

With continued support from the Hemp Research Institute, Bidwill and McKee plan to expand their business to include edible hemp products. As more states legalize marijuana for medical and recreational purposes, they hope their research will help guide better regulatory standards.

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