How strong is your weed? Study shows labels often misrepresent potency
While cannabis concentrates tend to be labeled accurately, about half of flower products are mislabeled
University of Colorado at Boulder
image:
A sampling of cannabis products purchased at Colorado dispensaries, including: three kinds of loose flower (a, b, c); a pre-rolled joint (d); shatter (e); Moroccan Hash (f); sugar (g); distillate concentrate (h)
view moreCredit: CU Boulder
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 funded by the Institute of Cannabis Research, the state’s official cannabis research institute, and 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 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% percent 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 flower,” 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 homogenous oils that are easier to analyze, whereas plants are inherently heterogenous 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, was more abundant than CBD in products across categories.
“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,” said Bidwell. “Our data suggests that multiple other cannabinoids should also be reported on there.”
What’s next? With support from the Institute of Cannabis Research, 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.”
Journal
Scientific Reports
Method of Research
Data/statistical analysis
Subject of Research
Not applicable
Article Title
Accuracy of labeled THC potency across flower and concentrate cannabis products
Article Publication Date
1-Jul-2025
COI Statement
D.I.M. and C.B. were employees of MedPharm Holdings (dba Bud & Mary’s) during the study period. MedPharm Holdings is a U.S. Drug Enforcement Administration (DEA) and State of Colorado licensed cannabis research company and a bulk manufacturer of cannabis products for the Colorado adult-use marketplace. MedPharm Holdings has no stake in any products tests in this study. G.G., M.O.T., G.M., C.S., J.L., and L.C.B. declare no competing interests.
Survey: A third of Californians use cannabis, but many don't know the risks
Most California cannabis users seek symptom relief; few ask their doctors for advice. This and other trends suggest a need for more public education on impacts of cannabis use.
Researchers at the University of California San Diego have completed a landmark survey of more than 5,000 Californians to study the effects of Proposition 64: The Adult Use of Marijuana Act, which made recreational cannabis use legal for adults 21 years of age and older across the state in 2016. The results of the survey, titled Impact 64, reveal that while many Californians are using cannabis regularly for both recreational and medicinal purposes, there are significant gaps in knowledge around cannabis use and its impacts. Initial results of the survey were recently published in the journal Cannabis and Cannabinoid Research.
"Our study provides the first comprehensive understanding of cannabis use patterns in California since the implementation of Proposition 64," said Linda Hill, M.D., M.P.H., principal investigator of Impact 64, distinguished professor at the UC San Diego Herbert Wertheim School of Public Health and Human Longevity Science, clinical professor at the School of Medicine and affiliated faculty at the Qualcomm Institute.
"It’s clear that a large portion of the population is using cannabis, but there are significant gaps in knowledge regarding laws and safety, and physicians are rarely consulted for advice on use. We need more targeted education initiatives for both cannabis users and medical providers.”
The new study found:
- 37% of California adults reported cannabis use in the past three months. 58% consumed cannabis daily, and 40% of users reported very frequent use (multiple times a day).
- 77% reported obtaining cannabis products from dispensaries, which the majority (94%) perceived as licensed.
- Regardless of self-categorization as a “medicinal” or “recreational user,” many participants reported improvements in emotional (82%), mental (81%) and physical (62%) health from cannabis.
- Although 78% felt comfortable discussing cannabis with their primary doctor, only 66% of participants reported that their physicians are aware of their cannabis use, and few users (15%) turn to medical providers for information and guidance about cannabis.
The passage of Proposition 64 in 2016 has driven rapid growth in California’s cannabis industry. The California Department of Cannabis Control (DCC) reports that there were more than $4.2 billion in cannabis sales across the state in 2024. As cannabis use becomes more mainstream with legalization in additional states, concerns have also increased about the risks it could pose to public health, such as impaired driving.
Impact 64, supported by the DCC, sought to evaluate cannabis use among adults in California in the post-Proposition 64 era, including frequency of use, sources, attitudes, relationship with health care providers, and sources of information about cannabis. By collaborating closely with Quester, a market research firm, the team was able to gather both qualitative and quantitative data with an AI-powered survey. Partnering with Quester also helped ensure that the study population was a representative sample of Californians, including native Spanish speakers.
“These methods allowed us to collect more in-depth data than is possible in a typical survey-based study,” said study co-author Renee Dell’Acqua, M.P.H, research program manager for the Herbert Wertheim School of Public Health’s Transportation Research and Education for Driving Safety (TREDS) center. “The result is an incredibly rich picture of how adults are using cannabis in California that can be used to inform future policy and public health initiatives.”
The study also assessed knowledge of the laws and behaviors related to cannabis use and driving, and these results are still pending publication. Future studies are also needed to explore cannabis-related attitudes, knowledge and practices among medical providers.
The research highlights the need for education and guidance on safe cannabis use practices, particularly given the prevalence of use in California.
“There is still much to be learned regarding the evolving world of legalized cannabis, including how it’s being used, by who, and the level of risks it may pose to public safety,” said Thomas Marcotte, Ph.D. co-principal investigator of Impact 64, professor of psychiatry and co-director of the Center for Medicinal Cannabis Research at UC San Diego School of Medicine. “The risk-benefit ratio for cannabis use is complex and warrants further study.”
Additional co-authors of the study include Daniel Ageze, Jill Rybar, and Sara Baird at UC San Diego Herbert Wertheim School of Public Health and Human Longevity Science and Alice Gold, Tom Shaughnessy and Ilene Lanin-Kettering at Quester.
This study was funded by the California Department of Cannabis Control (Grant #: 65334).
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Journal
Cannabis and Cannabinoid Research
DOI
Cannabidiol and liver enzyme level elevations in healthy adults
JAMA Internal Medicine
About The Study: In this randomized double-blind clinical trial of healthy adults administered cannabidiol (CBD), 5 mg/kg/d for 28 days, 8 (5.6%) experienced liver enzyme level elevations and 7 (4.9%) met protocol defined criteria for potential drug-induced liver injury. Participants did not experience clinical symptoms related to liver function during this 28-day study and hepatic enzymes returned to normal within 1 to 2 weeks following discontinuation. The findings of this study underscore the need for further investigation on the long-term effects of CBD use, its impact on various populations, and the safety of lower doses commonly used by consumers.
Corresponding Author: To contact the corresponding author, Jeffry Florian, PhD, email jeffry.florian@fda.hhs.gov.
To access the embargoed study: Visit our For The Media website at this link https://media.jamanetwork.com/
(doi:10.1001/jamainternmed.2025.2366)
Editor’s Note: Please see the article for additional information, including other authors, author contributions and affiliations, conflict of interest and financial disclosures, and funding and support.
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Journal
JAMA Internal Medicine
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