A report in The Lancet by a team led by Dr Stanley Zammit from Bristol and Cardiff Universities said young people needed to be made aware of the dangers. In an additional article, experts said up to 800 schizophrenia cases a year in the UK could be linked to cannabis use.
The researchers looked at 35 studies on the drug and mental health. Some experts urged caution over the results. The study found the most frequent users of cannabis have twice the risk of non-users of developing psychotic symptoms, such as hallucinations and delusions.
The evidence for a link with depression and anxiety was less clear, they said. However, they said they could not rule out the possibility that people at a higher risk of mental illness were more likely to use the drug.