Cannabis use increases likelihood of psychosis: researcher

New research has found people who start using cannabis from a young age are up to three times more likely to suffer from psychotic illness.

The Queensland Brain Institute (QBI) study found young adults who used the drug for six years or more from the age of 14 had the greatest risk of developing symptoms.

QBI lead researcher Professor John McGrath says the study of almost 4,000 people also included more than 200 sets of siblings.

He says the research supports other findings on the risks of drug use.

"We compared the duration since first cannabis use in one brother versus the other brother and we found a very consistent pattern that the duration of cannabis was linking to psychosis scores," he said.

"So that allows us to tighten up the research a little bit more."

Professor McGrath says young adults need to be more aware of the dangers.

"We may have thought that cannabis is safe but in fact for young people in particular there are risks involved," he said.

"Everything we do has risks involved - whether we drive or ride a bike or use alcohol - and I think it's important that young people know that if you use cannabis from an early age you do increase your risk of a psychotic disorder."