People who self-harmed as teens are more than twice as likely to be weekly cannabis users at the age of 35, Australian researchers say.

Teenagers who self-harm are more likely to suffer mental health problems, have substance abuse issues and relationship failures, even decades after the behaviour stops, a new study suggests.

For the past 20 years, researchers from the Murdoch Children's Research Institute have been tracking the same set of Victorian teenagers and the results are clear.

The risks of self-harm don't end when the behaviour stops and can extend almost to middle age, and possibly beyond.

The study began in August 1992 and has tracked health and life outcomes for 1943 Victorians.

Participants were 14 when they were randomly selected from 44 schools across Victoria, and regular follow ups have revealed relatively poor prospects for the 135 who harmed themselves at least once during their teenage years.

At the last check in, when participants were 35, self-harmers were found to be more likely to suffer from mental health conditions such as anxiety and depression.

They were also more likely to smoke and take drugs, had higher divorce rates, and were more likely to suffer various forms of social disadvantage, including unemployment.

MCRI psychologist Rohan Borschmann, lead author of a newly published update on the study, says the findings should help guide how health and other professionals help self-harming adolescents adjust to adult life.

"We've shown problems persist until at least 35 so any kind of intervention should focus on multiple domains," he says.

"Just having some sort of intervention that focuses on self-harm probably won't be sufficient. It also has to look at mental health issues, substance abuse issues, school engagement. A multi-faceted intervention shows the best promise."

Dr Borschmann said most of the problems reported by self-harmers when they reached their mid-30s could be partly explained partly by factors such as the mental or substance abuse issues they suffered as teens.

But there was one standout finding. People who self-harmed as teens were more than twice as likely to be weekly cannabis users at the age of 35.

"We showed adult cannabis use was independently associated with self harm, and that behaviour wasn't accounted for by prior substance abuse or self harm," Dr Borschmann said.

The research paper has been published in the journal Lancet Child and Adolescent Health.