Approximately 147 million people worldwide consume cannabis, or marijuana each year; a number that continues to grow, especially in North America and Europe, according to the World Health Organization.
At the same time, the cannabis available today is more potent than ever before. A systematic review published in Addiction found that levels of tetrahydrocannabinol (THC)—the active ingredient in marijuana—has been increasing for decades. The review found that, in a gram of herbal cannabis, the part typically smoked, THC concentrations have increased by approximately 2.9 milligrams each year since the 1970s. A standard dose of THC is considered to be between 5 and 10 mg, which typically produces a mild intoxication for non-regular users. In the review, researchers measured concentrations as high as 20 mg of THC per gram of herbal cannabis.
Now, new research finds that higher concentrations of THC lead to higher rates of addiction and mental health problems. The data come from a new meta-analysis published in the journal Lancet Psychiatry that included 20 studies comparing the effects of higher and lower potencies of marijuana.
The authors found that participants who used higher-potency marijuana were more likely to experience psychosis than those who used lower-potency marijuana. Higher potency marijuana, especially when used daily, also led to an increased risk of psychotic relapse.
Users of higher potency marijuana are also more likely to become addicted to the drug and develop more severe dependence. One study found that higher-potency marijuana was four times more addictive compared to lower-potency marijuana.
The review found that the effect of higher potency marijuana on depression and anxiety is unclear.
The take-home message: The increasing potency of marijuana is leading to more addiction and a higher incidence of psychosis among marijuana users. A major problem is that most users who buy marijuana off the street don’t have any way to measure its potency. Marijuana users should be careful about how much they use.