A group of scientists in the United States, United Kingdom, Europe and Australia is warning about the potential mental health consequences of marijuana use, The Guardian reports. They say frequent use of marijuana increases the risk of psychotic disorders in vulnerable people.

The scientists are calling for global public health campaigns to warn the public about marijuana’s risks. They say the vast majority of people who smoke marijuana do not develop psychotic disorders. But those who do can suffer from hallucinations, delusions and irrational behavior. Most people recover from these episodes, but some go on to develop schizophrenia, the article notes. Heavy marijuana use is associated with an increased risk.

“It’s not sensible to wait for absolute proof that cannabis is a component cause of psychosis,” said Sir Robin Murray, Professor of Psychiatric Research at King’s College London. “There’s already ample evidence to warrant public education around the risks of heavy use of cannabis, particularly the high-potency varieties. For many reasons, we should have public warnings.”

Research suggests deterring heavy marijuana use could prevent 8 percent to 24 percent of psychosis cases handled by treatment centers, experts told the newspaper.

The strength of marijuana is increasing. Over the past two decades, the strength of marijuana seized by the U.S. Drug Enforcement Administration increased from 4 percent to 12 percent THC, the psychoactive ingredient in the drug. An estimated 22.2 million Americans used marijuana in 2014, according to the National Institute on Drug Abuse (NIDA).

“It is important to educate the public about this now,” said NIDA Director Nora Volkow. “Kids who start using drugs in their teen years may never know their full potential. This is also true in relation to the risk for psychosis. The risk is significantly higher for people who begin using marijuana during adolescence. And unfortunately at this point, most people don’t know their genetic risk for psychosis or addiction.”