Marijuana: Why Dangerously Potent Pot Is Making People Lose Their Minds and Memories

High-potency pot is causing psychiatric issues, including addiction and memory problems. New strains of the recreational drug have higher levels of the active chemical and not enough of another compound that keeps the drug safe. And as a new study this week documents, the riskiest pot is coming from the black market—which could be an argument for expanding legalization.

The new report, published this week by Manchester Metropolitan University in the U.K., tested 50 samples of cannabis in the city of Manchester. The study was conducted by Volteface, a London-based policy think tank seeking reform for marijuana laws to improve safety of the drug by making it legal, and thus limiting demand on the local black market. All of the samples had high levels of tetrahydrocannabinol (THC), the psychoactive component of the drug that produces the "high," and inconsequential amounts of cannabidiols (CBDs), the protective compound of the drug that prevents marijuana from becoming unsafe.

Pot that is high in THC carries a greater risk of psychiatric problems, including psychosis, addiction and memory impairment. One study, for example, published in the British Journal of Psychiatry evaluated cannabis use in 280 people and compared them to a control group of 174 non-cannabis users. The study found that people who experienced their first psychotic episode were more likely to have used a higher THC potency form of the drug.

Amir Englund, an expert in cannabinoid psychopharmacology at the Institute of Psychiatry, Psychology and Neuroscience at King's College London, tells Newsweek that the low levels of CBDs exacerbate the issues caused by high levels of THC. Additionally, frequent users often become tolerant to cannabis and slowly need a stronger product to get as high as they used to, he says.

"Because both THC and CBD are made from the same material in the plant, more of one means less of the other," he says. Some recent research, he says, has shown that people using strains of marijuana that are also high in CBD—not just THC—are less likely to have mental health problems than those who opt for strains that have low CBD but high THC content. Some experiments he's conducted show that CBD can counter the negative effects of high doses of THC in healthy volunteers.

Growers, he says, are cross-breeding plants to favor THC production over CBD. But the decision isn't influenced only by the market's demand. In many instances, it's determined by the grower's bottom line. "Some of the reasons why these varieties are more popular include the fact that they are more cost-effective to produce (more total drug-yield per plant) and more popular among frequent users," says Englund.

A number of other factors also affect the potency of pot. According to Leafly, there will always be some variation when multiple growers cultivate the same strain because environment, growing technique and genetics all impact the composition of the plants.

A report published in 2015 by the Colorado Department of Public Health and Environment found the problem isn't only with illegal sales. Labeling on regulated cannabis is often misleading, and the strain purchased could have higher or lower levels of potency than the label leads a consumer to believe.

"High THC, low CBD cannabis dominates the UK's illicit market as it has a rapid growth period up to maturity and can be grown indoors," the researchers write. "This enables those selling cannabis to make the greatest profit and presents the lowest risk. While popularity of this product is undoubtedly high, this may well be due to the fact that no other product is easily available and consumers have neither the access to nor the experience of any alternative."

In other words, pot purchasers should look beyond the name—as nice as Black Beauty and Northern Lights may sound—and find out more about what they're smoking.