'Link found' between cannabis and harder drugs

Cannabis users are almost certain to try other illicit drugs, latest research findings suggest.

Research at the Christchurch School of Medicine and Health Sciences looked at the relationship between the use of cannabis and other illicit drugs in a sample of 1000 young people aged between 15 and 25.

The Otago University study showed high rates of both cannabis and illicit drug use, with almost 80 per cent of the sample using cannabis by the age of 25 and more than 40 per cent using other illicit drugs.

It found that in the great majority of cases the use of cannabis preceded the use of other illicit drugs.

Principal investigator David Fergusson said today the question of whether cannabis use increased the risk that young people would use other drugs had been the subject of long debate.

Professor Fergusson said the latest findings, from the Christchurch Health and Development Study, could suggest a "cause and effect relationship" where cannabis use encouraged the use of other drugs.

It had often been suggested that associations between cannabis and other illicit drug use arose from common factors that predisposed young people to use cannabis and other drugs.

However, Prof Fergusson said the Otago University study applied complex statistical methods to address that issue and found that even following statistical controls, there was a clear tendency for cannabis users to have higher rates of usage of other drugs.

The tendency was most evident for regular cannabis users and was more marked in adolescents than in young adults.

Evidence from the study favoured the view that cannabis may encourage the use of other drugs. Cannabis may lead to changes in brain chemistry that make young people more susceptible, or experiences with cannabis may encourage experimentation with other drugs.

In addition, Prof Fergusson said, because cannabis use was illegal, users often obtained supplies from the black market, exposing them to drug dealers.

"Our research shows the regular use of cannabis increases the risks that young people will try other illicit drugs," he said.

"What's not clear are the underlying processes that lead to this association. Understanding these processes is critical to how we view cannabis."

Prof Fergusson said if the association arose because using cannabis increased contact with illegal drug markets, it would support arguments for the decriminalisation or legalisation of cannabis.

"If, however, the association arises because using cannabis encourages young people to experiment with other illicit drugs, the results could be seen as supporting the prohibition of cannabis use," he said.

- NZPA