Scientists Reveal Inaccurate Weed THC Labels

COLORADO — A new study from the University of Colorado and MedPharm Research reveals that nearly 50% of cannabis flower products sold in Colorado carry THC labels that do not match their actual potency. The research highlights inconsistencies in testing and labeling practices that could mislead consumers regarding both strength and safety.

The statewide review, funded by the Institute of Cannabis Research, tested 277 cannabis products from 52 licensed dispensaries across 19 counties. Researchers examined 178 flower products, including loose flower and pre-rolled joints, and 99 concentrates such as oils, waxes, and hash. Edibles were not part of this stage of the study.

Testing revealed a significant discrepancy between labeled and actual THC content for flower products. About 44% failed to meet Colorado’s standard of being within 15% of the stated THC level. Most of these overestimated potency, while a smaller number contained more THC than indicated. In contrast, concentrates were far more accurately labeled, with only four products showing inconsistencies.

“Accurate THC information is critical, whether for medical use or recreational consumption,” said L. Cinnamon Bidwell, senior author of the study and associate professor at CU Boulder. “Users need reliable information to avoid unintentional overconsumption and associated risks.”

The study also highlighted the rise of ultra-potent cannabis. Flower products averaged 21% THC, while concentrates reached 71% on average, with some exceeding 80%. By comparison, marijuana in the 1980s typically contained about 8% THC.

Researchers identified several factors contributing to labeling discrepancies. Flower plants are inherently heterogeneous, making potency more difficult to measure than homogenized concentrates. In some cases, third-party labs may inflate THC results to attract business from marketers seeking higher potency claims.

Beyond THC, the study found that other cannabinoids such as cannabigerol (CBG) and cannabigerolic acid (CBGA) were present in higher concentrations than CBD in many products, despite labels rarely reflecting these compounds. Only 16% of products reported cannabinoids beyond THC and CBD, though these compounds may have notable therapeutic benefits, including anti-inflammatory and anti-anxiety effects.

“Focusing solely on THC can mislead consumers and underrepresent the value of other cannabinoids,” said Duncan Mackie, co-author and director of pharmacology at MedPharm. “Future labeling should provide a more complete cannabinoid profile to guide informed choices.”

The researchers plan to expand their work to include cannabis edibles and hope their findings will inform regulatory standards and industry practices as legal cannabis markets continue to grow nationwide.

Reference: Giordano, G., Brook, C. P., Ortiz Torres, M., MacDonald, G., Skrzynski, C. J., Lisano, J. K., Mackie, D. I., & Bidwell, L. C. (2025). Accuracy of labeled THC potency across flower and concentrate cannabis products. Scientific Reports, 1 July 2025. DOI:10.1038/s41598-025-03854-3