Teenagers who use cannabis are at 11 times higher risk of developing a psychotic disorder, according to a study on 22 May.

The study, published in the journal Psychological Medicine, is the first to show an age-dependent association between self-reported cannabis use and subsequent psychotic disorder diagnosis.

It suggests that the association between cannabis and psychotic disorders may be stronger than indicated by previous research. "We found a very strong association between cannabis use and risk of psychotic disorder in adolescence.

Surprisingly, we didn't find evidence of association in young adulthood," said lead author Andre McDonald, a postdoctoral fellow at Medicinal Cannabis Research at McMaster University, Canada.

"These findings are consistent with the neurodevelopmental theory that teenagers are especially vulnerable to the effects of cannabis," he added.

The team surveyed data from over 11,000 youth in Ontario and found that "most teenagers who are diagnosed with a psychotic disorder likely have a history of cannabis use".

The study adds to worries about early cannabis use, particularly as commercialised cannabis products, with a higher psychoactive compound, tetrahydrocannabinol or THC content, have become more widely available.

THC is known to affect thinking, learning, and remembering, create anxiety, panic, or paranoia, and lead to a faster heart rate and increased blood pressure. The expert called for developing prevention strategies targeting teenagers.