A man sitting with two jars of pot

Consumers who live in states with legalized private cannabis markets have access to more potent and chemically diverse pot than marijuana researchers. 

National Geographic Creative/Alamy Stock Photo

Government pot is less potent than commercial pot, questioning dozens of scientific studies

Earlier this week, four U.S. states voted to legalize recreational use of marijuana, whereas four states made it legal as just a medicine. But as national tolerance grows for the drug, a new study suggests the marijuana in circulation bears little resemblance to what the government requires federally funded academics to use, a handful of special strains approved by the U.S. National Institute on Drug Abuse (NIDA). The finding calls into the question the validity of dozens of studies based on the government-grown marijuana.

The U.S. federal government instituted strict taxes on marijuana sales and use in 1937 that, in effect, made it illegal. But it wasn’t until 1970 that the feds slapped the drug with a Schedule I designation, the country’s strictest level of controlled substances. Around the same time, the Bureau of Narcotics and Dangerous Drugs, the Drug Enforcement Administration’s (DEA's) predecessor, began regulating marijuana cultivation for research. Ever since, the University of Mississippi has held an exclusive contract to grow marijuana destined for laboratory experiments, from studying its effects on driving ability to investigating whether it can help treat glaucoma.

But do the findings from that work accurately reflect the experiences of people who regularly use marijuana? Probably not, says Nolan Kane, a plant geneticist at the University of Colorado (CU) in Boulder, who compared the chemical profiles of privately grown and government-grown marijuana in a study released last month. Researchers have suspected for years that NIDA’s marijuana has little in common with what’s available from private growers in terms of potency and chemical variety. But there have never been enough data to back that up. “Everybody knows this is the case,” he says, “but this is the first truly extensive study looking into it.”

With legislation poised to make marijuana more widely accessible, Kane and colleagues requested data from a private cannabis testing laboratory that dispensaries in Colorado, Washington, and California had hired to verify levels of psychoactive components including tetrahydrocannabinol (THC) in their retail pot. Steep Hill Labs, based in Berkeley, California, used high-performance liquid chromatography on 2980 marijuana samples to sort out individual molecules and compile a menu of its chemical compounds.

The primary compounds in marijuana are cannabinoids, which alter how neurotransmitters are released in the brain. THC is the best known, but others—only some of which have psychoactive effects—include cannabidiol, cannabigerol, cannabichromene, and tetrahydrocannabivarin. Though THC is often the primary focus of many federally funded studies, there’s increasing consensus within the field of cannabis research that many medicinal benefits of marijuana derive from various cannabinoids working in tandem, known as the “entourage effect,” Kane says.

The research team compared lab results from the privately grown cannabis samples with NIDA-provided information about the chemical composition of government-grown marijuana. Because Steep Hill tests for more compounds than NIDA, the researchers compared only those analyzed in both. Cannabinoid levels showed a great range in privately grown marijuana, which had diverse mixes of the various cannabinoids and other compounds called terpenes. The federally grown strain, in contrast, had a “limited diversity,” the researchers reported last week on the preprint server bioRxiv. Importantly, THC levels on average were between 10% and 15% lower in NIDA-sanctioned pot than in the least potent samples in legal dispensaries. “In NIDA’s marijuana, you pretty much only get THC,” Kane says. “That doesn’t seem like a good analog for what’s going on in the private market.”

Daniela Vergara, a postdoctoral scholar in Kane’s lab at CU who led the study, notes that the euphoric effects, as well as some of the suspected therapeutic benefits, of cannabis ramp up with its dosage. The researchers conclude that less potent and less chemically diverse pot prevents researchers from discovering the effects—both good and bad—of the cannabinoids prevalent in privately grown strains. “The bottom line is that if you can’t have people consuming the cannabis they usually consume, then your research is not going to be valid,” Vergara says.

NIDA declined to comment on the paper, but in a prepared statement, the agency noted that it has diversified its cannabis offerings to researchers since 2014. The statement also noted that NIDA supports a recent DEA decision to increase the number of farms eligible to grow marijuana for research “to potentially increase the variety and strains available to scientists.”

Kane says this is a good start, but it doesn’t compare to the vast array of cannabinoid compositions found on the private market. Kane and Vergara would ideally like to see federal guidelines revised to allow researchers to test any legally sold cannabis strains.

Ethan Russo, a neurologist and psychopharmacology researcher at Phytecs in Los Angeles, California—a biotech firm that studies naturally made endocannabinoids—agrees. If U.S. researchers had access to privately grown cannabis, the state of the science would rapidly improve, Russo says. “Because of the constraints on this research, we’ve taken a backseat to the rest of the world. We should be leading.”