Colorado Study Finds Retail Cannabis Flower Often Tests Below Its THC Label
A 2023 peer-reviewed study found that many cannabis flower products purchased from Colorado dispensaries contained substantially less THC than their labels indicated. Researchers tested 23 samples from 10 dispensaries along the Colorado Front Range and compared the results with the potency information printed on the packaging.
The study, published in PLOS ONE, used high-performance liquid chromatography to measure total THC. The samples had an average observed potency of 14.98%, while the labels reported average minimum and maximum values of 20.27% and 24.10%, respectively.
Eighteen of the 23 samples—78.3%—contained less THC than the lowest potency value listed on the label. In 16 samples, or 69.6%, the measured potency was more than 15% below that minimum label value. Thirteen samples were more than 30% lower, and the largest discrepancy was 56.5% below the reported potency.
The researchers described the sampling as opportunistic rather than representative of every Colorado dispensary, strain, or testing laboratory. The sample was also relatively small. As a result, the findings show a substantial discrepancy among the products tested but do not establish how common the problem is across the entire state market.
The study also did not directly prove that laboratories or cannabis businesses manipulated test results. However, the authors identified several possible incentives for inaccurate potency reporting. Consumers often use THC percentage when comparing products, and products advertised as more potent may command higher prices. The paper discusses “lab shopping”—the practice of seeking out a laboratory that produces more favorable results—as one possible industry-level concern, but it was not measured in the study itself.
Accurate labeling matters because THC concentration is one factor consumers may consider when deciding how much cannabis to use. It can be particularly important for people who are inexperienced with cannabis or who use it for medical purposes. The Centers for Disease Control and Prevention notes that THC can affect memory, attention, decision-making, coordination, and reaction time, while the effects of higher-concentration products can carry additional risks.
Colorado requires cannabis products to undergo testing for potency and contaminants. The state’s 2024 Marijuana Handbook explains that testing laboratories must meet accreditation requirements and that marijuana samples are tested for cannabinoids as well as substances such as pesticides, solvents, and mold. The Colorado study nevertheless suggests that compliance with a testing system does not necessarily guarantee that a label accurately reflects the product purchased by a consumer.
The authors called for larger studies involving more products, states, laboratories, and product types. They also pointed to the need for stronger oversight and more consistent testing practices. For consumers, the findings are a reminder that a printed THC percentage should be treated as an estimate of potency—not as a perfectly precise measurement.
