These findings come from a large-scale analysis of cannabis products purchased from licensed dispensaries across Colorado, the first state to legalize recreational marijuana. Published in Scientific Reports, the study represents the most detailed audit yet of legal-market cannabis labeling. It offers new insight into how potent today's cannabis has become, what testing and labeling practices are working, and where the system still falls short.

"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 project was funded by the Institute of Cannabis Research, Colorado's official state research institute, and carried out in partnership with MedPharm Research, LLC, a licensed 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.

How the Research Was Conducted

Because federal law prevents university scientists from directly purchasing or handling cannabis from the legal market, industry collaboration was essential, explained first author Gregory Giordano, a professional research assistant in CU Boulder's Department of Psychology and Neuroscience.

A MedPharm "secret shopper" traveled throughout the state to collect 277 cannabis products from 52 dispensaries across 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 hash and waxy "sugar." Edibles were not part of this phase of research.

Photographs of each label were provided to Bidwell's team. The samples, identified only by number, were then tested by MedPharm chemists who did not see the original labels to ensure objectivity.

What the Tests Revealed

On average, cannabis flower products contained about 21% 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 around 8% THC.

"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.

Why Potency Labels Can Differ

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: Other Cannabinoids Matter Too

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."

Looking Ahead: Improving Cannabis Labeling

With continued support from the Institute of Cannabis Research, Bidwell and Mackie plan to expand their work to include edible cannabis products. As more states legalize marijuana for both medical and recreational purposes, they hope their research will help guide better regulatory standards.

"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."

Clive Svendsen, PhD, executive director of the Board of Governors Regenerative Medicine Institute and senior author of the study, explained the team's innovative approach. "Previous studies have shown that transfusions of blood or plasma from young mice improved cognitive decline in older mice, but that is difficult to translate into a therapy," Svendsen said. "Our approach was to use young immune cells that we can manufacture in the lab -- and we found that they have beneficial effects in both aging mice and mouse models of Alzheimer's disease."

Creating Youthful Immune Cells From Stem Cells

The cells, known as mononuclear phagocytes, normally circulate through the body to clear harmful substances. However, their function diminishes as organisms age. To produce youthful versions, researchers used human induced pluripotent stem cells -- adult cells reprogrammed to an early embryonic-like state -- to generate new, young mononuclear phagocytes.

When these lab-grown immune cells were infused into aging mice and mouse models of Alzheimer's disease, the scientists observed remarkable improvements in brain function and structure.

Improved Memory and Brain Cell Health

Mice that received the young immune cells outperformed untreated mice on memory tests. Their brains also contained more "mossy cells" within the hippocampus, a region essential for learning and memory.

"The numbers of mossy cells decline with aging and Alzheimer's disease," said Alexendra Moser, PhD, a project scientist in the Svendsen Lab and lead author of the study. "We did not see that decline in mice receiving young mononuclear phagocytes, and we believe this may be responsible for some of the memory improvements that we observed."

In addition, the treated mice had healthier microglia -- specialized immune cells in the brain responsible for detecting and clearing damaged tissue. Normally, microglia lose their long, thin branches as the brain ages or in Alzheimer's disease, but in treated mice, these branches remained extended and active, suggesting preserved immune and cognitive function.

How the Treatment Might Work

The exact mechanism behind these benefits is not yet clear. Because the young mononuclear phagocytes did not appear to cross into the brain, researchers believe they may influence brain health indirectly.

The team proposes several possibilities: the cells could release antiaging proteins or tiny extracellular vesicles capable of entering the brain, or they might remove pro-aging factors from the bloodstream, protecting the brain from harmful effects. Ongoing studies aim to identify the precise mechanism and determine how best to translate these findings into human therapies.

Toward Personalized Anti-Aging Therapies

"Because these young immune cells are created from stem cells, they could be used as personalized therapy with unlimited availability," said Jeffrey A. Golden, MD, executive vice dean for Education and Research. "These findings show that short-term treatment improved cognition and brain health, making them a promising candidate to address age- and Alzheimer's disease-related cognitive decline."

Additional authors include Luz Jovita Dimas-Harms, Rachel M. Lipman, Jake Inzalaco, Shaughn Bell, Michelle Alcantara, Erikha Valenzuela, George Lawless, Simion Kreimer, Sarah J. Parker,andHelen S. Goodridge.

Funding: This work was supported by the Universal Sunlight Foundation, the Cedars-Sinai Center for Translational Geroscience, and the Cedars-Sinai Board of Governors Regenerative Medicine Institute.