An international study involving Queensland researchers has found a genetic link between mental illness and cannabis use.

A major international study has found people with certain mental disorders including schizophrenia have a higher genetic disposition to use cannabis.

The study, published in the journal Nature Neuroscience on Tuesday, found 35 genes that influence whether people are likely to ever use the drug.

Professor Eske Derks from Queensland's QIMR Berghofer Institute was part of the international team of scientists who worked on the study.

Professor Derks said they found a "genetic overlap" between cannabis use and use of tobacco and other substances, as well as a risk of developing schizophrenia and bipolar disorder.

"In other words, the genes that increase the likelihood of cannabis use also influence these other traits and conditions."

It had previously been thought that cannabis use caused mental disorders, but Professor Derks said this study seemed to confirm the alternate theory that it merely exacerbated underlying conditions.

"This may suggest that people with schizophrenia use cannabis to cope with the symptoms," Professor Derks said.

"These findings don't rule out the possibility that cannabis use could also contribute to the onset of schizophrenia; however, we haven't found any evidence to support that in this study."

The next step for researchers is to find out exactly which genes influence how frequently people use cannabis and the amount they use.

The study was conducted by researchers in Australia, Radboud University in the Netherlands and Virginia Commonwealth University in the US.

It used DNA samples from more than 180,000 people worldwide via 23andMe, the UK Biobank and 16 other studies.