Illicit drugs 'can speed up psychosis'

Professor Jon Currie says early use of drugs is a risk for all young people. Photo: Louis Douvis

YOUNG people at risk of schizophrenia can speed up the condition's onset by one year for every illicit drug they take, new Australian research has revealed.

The study found heavy users of cannabis, cocaine and amphetamines experienced their first symptoms at a younger age than those who abstained or took only one drug.

Cannabis is known to increase the risk of developing psychotic illnesses earlier, but this is the first evidence that taking additional drugs further accelerates the process.

The research, involving 167 men, showed the mean age of onset of schizophrenia for non-drug users was 23.3 compared with 22.5 for those who had smoked cannabis.

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Men who had used cannabis and amphetamines developed the illness at a mean age of 20.8, while the onset for those who used cannabis, amphetamines and cocaine was 19.6.

Published in the latest edition of the Australian and New Zealand Journal of Psychiatry, the findings - involving West Australian psychiatric patients - have prompted calls for public health campaigns to warn young people against multiple drug use.

''If you can delay the age of onset of the illness in a person who is predisposed to schizophrenia, you open potential ways by which you can intervene early, and what our study shows is that these major drugs do indeed bring forward the age of onset compared with young people who never took drugs before they got ill,'' said the study's co-author, Professor Nikos Stefanis, from the University of Western Australia.

''Research shows that the longer a person is psychosis-free, the easier their condition is to treat when they start having symptoms.

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Illicit drugs 'can speed up psychosis'