Crack smokers are at a 40 percent greater risk of developing schizophrenia and a regular intake can increase the risk two fold, says a new study.
Australian researchers focussed their study on latest evidence of links between cannabis use and mental illness and found that the association is "stronger and clearer than ever".
The review found that a pot smoker is 40 per cent more likely to suffer a psychotic episode than a non-smoker and for daily smokers the risk is 200 per cent higher.
"On the world stage, Australians excel in smoking cannabis, so there are very many people who fit into this category," News.com.au quoted Dr Martin Cohen lead researcher and a psychiatrist at the Hunter New England Mental Health Service.
"In fact we're number one in the world. We know now more than ever that this bodes badly for our mental health," he added.
A third of all Australians have smoked at least once in their life, with about 300,000 using daily.
The researchers discovered that a gene called COMT, when faulty, is incapable to break down the brain chemical dopamine.
An overload of dopamine triggers psychosis and, as cannabis produces an excess of the chemical, people with this "fault" are vulnerable.
Between 10 and 25 per cent of the population are believed to have the faulty gene, but as yet there is no way to test for it.
A national survey conducted in 2007 of 14 to 19 year olds revealed that 20 per cent had ever smoked marijuana and 13.1 per cent had smoked in the last 12 months.
"These teenagers are the ones we really need to worry about because their use is changing a developing brain," said Cohen.
The review is published in the latest Australian and New Zealand Journal of Psychiatry.