When a customer buys a cannabis product labeled 25% THC, they expect that level of potency. Yet, new research from the University of Colorado Boulder shows this often isn’t true.
Nearly half of all tested cannabis flower products contained less THC than labels claimed, raising concerns about labeling accuracy and consumer trust in Colorado’s legal marijuana market.
The study, published in Scientific Reports, examined 277 cannabis products from 52 dispensaries across 19 Colorado counties, making it the largest independent audit of this type.
Researchers found that 44% of cannabis flower products did not meet the state’s labeling accuracy standard, which allows a 15% margin of error between labeled and actual THC. By contrast, 96% of cannabis concentrates were labeled accurately.
“Cannabis use has complex and wide-ranging effects, and we are working hard to better understand them,” co-author and associate professor of psychology and neuroscience at CU Boulder, Dr. Cinnamon Bidwell, said in a press release. “While that research plays out, we should, at the very least, be providing accurate information about the amount of THC in these products.”
Colorado, the first state to legalize recreational marijuana, has long served as a testing ground for the nation’s cannabis policies. Yet until now, no one had independently verified whether the THC numbers printed on dispensary labels matched the real chemical content inside the products.
For the study, researchers worked with MedPharm Research LLC, a state-licensed testing facility and manufacturer. Due to federal law, university scientists can’t handle retail cannabis, so MedPharm purchased and analyzed products blindly to avoid bias.
A secret shopper collected labeled, photographed samples of flower and concentrate products. MedPharm chemists then used high-performance liquid chromatography (HPLC) to analyze the samples without reference to the original labels.
Results showed flower products averaged 21% THC, while labels claimed an average of 22.5%. Concentrates averaged 70.7% THC, closely matching their labeled average of 73%.
Some flower products had slightly more THC than listed, but most overstated their potency, sometimes significantly. One product labeled 24% THC tested at just 16%.
On average, the difference between labeled and observed THC was about 2%.
A 2% THC difference may seem minor, but researchers say it can affect both medical and recreational users. For medical patients relying on specific doses, inaccurate potency could harm treatment. For recreational users, it could cause unexpectedly strong or weak effects and possible health risks.
“THC content has increased significantly, and we know that greater THC exposure is likely associated with greater risks, including risk of cannabis use disorder and some mental health issues,” Dr. Bidwell explained.
The findings have policy implications. Inaccurate labeling can erode consumer confidence and distort the market, especially since higher THC levels command premium prices.
Co-author and director of pharmacology at MedPharm, Duncan Mackie, emphasized the need for transparency. “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,” he said.
The study suggests multiple reasons why flower products may be more prone to inaccurate labeling than concentrates. Unlike concentrates, which are made from homogenized oils and are easier to analyze, raw plant material is inherently variable. Even within a single batch, THC levels can differ across buds depending on light exposure, curing, and storage.
Previous investigations in states like Washington and California have shown that some third-party labs may also inflate THC numbers to attract business from producers seeking to market “stronger” products.
A 2023 study of California and Colorado dispensaries found over 70% of flower products failed accuracy thresholds, with almost all overstating potency.
The Colorado team didn’t investigate whether deliberate inflation played a role, but noted that the market pressure to advertise higher THC remains a possible factor.
While THC remains the star of most cannabis marketing, the study highlights a blind spot in labeling: other cannabinoids. Colorado requires companies to list CBD levels, but only 16% of tested products included information about lesser-known compounds such as CBG (cannabigerol) and CBGA (cannabigerolic acid).
Interestingly, CBG and CBGA were more abundant than CBD in both flower and concentrate samples. These cannabinoids, believed to have anti-inflammatory and anti-anxiety properties, could play a significant role in how cannabis affects users, and yet, they’re largely invisible to consumers.
“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,” Dr. Bidwell said. “Our data suggests that multiple other cannabinoids should also be reported on there.”
The researchers hope their work will support better quality-control standards as legalization spreads. Accurate, consistent labeling could help consumers make safer, more informed choices and build trust in the market.
They plan to expand their analysis to edible cannabis products, a category known for inconsistency.
“We all want the same thing,” Mackie said. “A strong, successful industry that regulators can feel good about, businesses can thrive in, and customers can trust.”
Tim McMillan is a retired law enforcement executive, investigative reporter and co-founder of The Debrief. His writing typically focuses on defense, national security, the Intelligence Community and topics related to psychology. You can follow Tim on Twitter: @LtTimMcMillan. Tim can be reached by email: tim@thedebrief.org or through encrypted email: LtTimMcMillan@protonmail.com