Some people think of smoking pot as a rite of passage among teens—not an ideal one, certainly, but not an act that carries the same risk for serious harm as using harder drugs. However, a recent study highlights a significant flaw in the “pot is harmless” postulation by revealing a connection between marijuana use and an increased risk for symptoms of psychosis.

At the start of the study, nearly 2,000 people ages 14 to 24 answered questions about their history of marijuana use…and whether they had ever (while not high on a drug) experienced visual or auditory hallucinations, delusions or other psychotic symptoms. Participants updated their responses after 3.5 years…and updated them again five years later.

Findings: Among teens and young adults who reported no pot use or psychotic symptoms prior to the start of the study, those who used marijuana five or more times in the initial 3.5-year period were nearly twice as likely as abstainers to experience psychotic symptoms during the five-year period that followed. Also, among pot smokers who reported psychotic symptoms at 3.5 years, those who continued to use the drug in the following five years were significantly more likely to report persistent psychotic experiences than those who stopped smoking pot. The link between marijuana use and psychotic symptoms remained even after researchers adjusted for other psychosis risk factors, such as childhood trauma, other psychiatric diagnoses and use of other types of drugs.

This study does not prove that pot causes psychosis, but it does confirm an association between marijuana use and later development of this type of mental illness. Possible explanation: Transitory psychotic experiences are fairly common in the general population, but they can persist and progress to a full-blown psychotic disorder if combined with an environmental risk factor. Marijuana can be such an environmental factor, triggering psychosis in at-risk people in whom psychotic disorders otherwise might not ever have developed. Teens and young adults are at particular risk because their still-developing brains are more vulnerable to the effects of cannabinoids, the psychoactive compounds in marijuana.

Parents: Marijuana is the most commonly used illicit drug in the world, particularly among adolescents. Share the results of this study with your kids and explain that, despite pot’s reputation as relatively benign, the drug can have long-lasting negative effects on the brain that far outweigh the “fun” of a short-term high.