THC levels in weed often don't match what's promised on the label

The weed you’re buying might not make you as high as you hoped.

A study conducted by researchers at the University of Northern Colorado tested samples of cannabis sold at several Colorado dispensaries. Overall, they found that the product labels promised a potency higher than what was actually in the bags.

The study’s findings demonstrate the lack of regulation in the nation’s burgeoning cannabis industry and suggest that many buyers may be getting duped into believing their purchase will have a stronger concentration of THC, the psychoactive compound responsible for the euphoric “high” that weed delivers. Researchers say it is the first peer-reviewed study to examine empirically the potency of commercially available cannabis.

“I don’t believe what’s on the label,” said Mit McGlaughlin, one of the authors of the study and a professor of biological sciences at the University of Northern Colorado. “We just don’t have enough information for consumers about whether or not you can trust what’s being produced.”

To conduct the study, researchers bought 23 different samples of cannabis flowers from 10 dispensaries in Denver, Fort Collins and Garden City, Colo. They tested each sample to measure the concentration of THC, which stands for Delta-9-tetrahydrocannabinol.

In 18 of the 23 samples, which carried names including Sour Amnesia, Danky Kong and Colombian Gold ’72, the researchers found levels of potency below what was listed on the labels. Depending on the bag tested, some products contained 40 to 50 percent less THC than the labels promised. The amount of THC detected in the lab was, on average, 23 percent lower than the amount listed on the bags of cannabis.

Five samples contained levels of THC either within the range or close to those listed on the labels.

“These results make clear that consumers are often purchasing cannabis that has a much lower THC potency than is advertised,” the authors of the study concluded.

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Recreational cannabis is legal in 21 states and D.C., and it generates billions of dollars in annual sales. But researchers say there is not enough oversight of the dose of THC a person might get when buying marijuana, whether it is to be smoked, vaped or eaten. One reason for the lack of oversight is that cannabis remains illegal under federal law, meaning that standards related to retail and medical use vary by state.

“We have a hodgepodge of rules and regulations within each state,” said McGlaughlin. “It’s really hard to have to do that on a state-by-state basis.”

Just as breweries list the percentage of alcohol in bottles of beer, marijuana dispensaries often label bags of cannabis with the THC content. Researchers say the companies that grow cannabis typically send samples to third-party labs to measure the amount of THC in the plant. Often, the higher the concentration of THC, the higher the price.

This pricing dynamic has incentivized companies to grow, sell and market cannabis with higher concentrations of THC, says Anna Schwabe, the lead author of the study, which she conducted as a doctoral student at the University of Northern Colorado.

“It’s just kind of a mess right now,” said Schwabe, the director of research and development for a cannabis farm in New Jersey. “And, really, the folks who are at the short end of this stick are the consumers.”

People who regularly use marijuana to treat pain or insomnia, for example, may try to measure the amount of THC they’re taking, said Schwabe, who also is a lecturer at the University of Colorado at Boulder. It is difficult for consumers to judge accurately when the label does not match what they bought, Schwabe said.

“They’re not getting what they paid for,” Schwabe said. “This is not just a Colorado issue; this is a nationwide issue.”

In February, a patient with a medical marijuana license in Arkansas sued a cannabis testing lab and a cannabis farm for allegedly inflating claims about the amount of THC in the marijuana the person purchased. And two people filed a similar lawsuit in California in October, accusing a company of false advertisement over pre-rolled joints.

Jodi Gilman, the director of neuroscience at the Center for Addiction Medicine at Massachusetts General Hospital, said consumers cannot always trust what is on the labels of these products. In a clinical trial published in 2021, Gilman said people who thought they were taking CBD, another compound in cannabis that does not cause the same high, actually were unknowingly taking a cannabis product containing THC.

“That was a really scary experience for them,” said Gilman, who was not involved in the Colorado study. “You can’t always trust what’s on the label.”

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Schwabe said she first noticed the discrepancy in reported vs. actual THC while she was conducting a separate study on the smells of different strains of weed. She collected additional samples for the new research.

Schwabe and McGlaughlin sent samples of cannabis to a private lab. The lab researchers dissolved the cannabis buds in a solution and ran the resulting liquid through a chromatography machine that separated all the components of the plant according to molecular weight, McGlaughlin said. By doing so, they were able to determine the concentration of THC.

The amount of THC found in different parts of a cannabis plant can vary. Often, as you travel from the top to the lower limbs of a plant, the concentration of THC will fall, researchers say. Schwabe said advancements in the cultivation and growth of cannabis in recent decades has led to an overall rise in the amount of THC in weed. But she said she doesn’t think the increase is “as inflated as we have been led to believe.”

The THC in a cannabis bud can break down over time, especially if the weed isn’t stored correctly, researchers say. But, when THC degrades, it converts to cannabinol, which, according to the researchers, “was not observed in sizable quantities in the samples used in the study, indicating the lower potency in the observed versus reported values were not due to age or poor storage conditions.”

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