June 11 (UPI) -- High-potency marijuana flower and concentrates don't get users any more intoxicated than lower potency forms, according to a study published Thursday by JAMA Psychiatry.
While users of marijuana concentrates have blood levels of tetrahydrocannabinol, or THC, more than twice those of who smoke flower, their self-reports of intoxication, or "feeling high," were remarkably similar. So were their measures of balance and cognitive impairment, the authors found.
THC is the main psychoactive component of marijuana.
"Surprisingly, we found that potency did not track with intoxication levels," study co-author Cinnamon Bidwell, an assistant professor in the University of Colorado-Boulder's Institute of Cognitive Science, said in a statement.
"While we saw striking differences in blood levels between the two groups, they were similarly impaired," Bidwell said.
In all, 33 states have legalized medicinal marijuana use, and 11 have legalized recreational use of the drug, although it remains illegal at the federal level, according to Bidwell and her colleagues.
Researchers are prohibited from handling or administering marijuana, although some have used strains supplied by the government, which contain far less THC than real-world products, they said.
To test the marijuana products people really use, Bidwell and her colleagues employed two Dodge Sprinter vans they call "cannavans" as mobile laboratories. They drove the vans to the residences of study subjects who purchased cannabis on their own, consumed it and then walked outside for tests, they said.
For the current study, funded in part by the Colorado Department of Public Health and Environment, the team assessed 121 regular cannabis users, according to the researchers.
Half typically used concentrates -- oils, extracts and waxes that include the active ingredients without leaves or stems -- while rest used flower from the plant, with leaves and stems, they said.
Flower users purchased a product containing either 16 percent or 24 percent THC, while concentrate users were assigned to a product containing either 70 percent or 90 percent THC, the researchers noted.
On test day, Bidwell and her team drew the participants' blood, measured their mood and intoxication level and assessed their cognitive function and balance at three points -- before, directly after and one hour after they used marijuana.
Those who used concentrates had much higher THC levels at all three points, with levels spiking to 1,016 micrograms per milliliter in the few minutes after use, while flower users peaked at 455 micrograms per milliliter, the analysis found.
Among all users, balance was about 11 percent worse after using cannabis, and memory was compromised up to one hour after use, the researchers said.
The researchers aren't sure how the concentrate group could have such high THC levels without greater intoxication, but they suspect that regular users of concentrates likely develop a tolerance over time.
Genetic or biological differences that make some people metabolize THC more quickly might exist, too, they said.
Also, once compounds in marijuana, called cannabinoids, fill receptors in the brain that spark intoxication, additional cannabinoids might have little impact, the researchers said.
The findings also raise concern that using concentrates could unnecessarily put people at greater long-term risk of side effects, the authors said. Ultimately, the researchers hope to learn what, if any, long-term health risks concentrates pose.
"It raises a lot of questions about how quickly the body builds up tolerance to cannabis and whether people might be able to achieve desired results at lower doses," Bidwell said.