Many harms associated with cannabis use result from prohibition rather than the drug itself, an Australian academic has told a United Nations review of drug policy.

Professor Robin Room, a sociologist at the University of Melbourne's School of Population Health has spent much of the past week telling meetings in Vienna that international conventions on cannabis are out of touch and do little to influence the number of users.

Prof Room said while penalties were generally low for cannabis use and possession globally, young people and minorities were more likely than other groups to become caught up in the legal system.

Arrests caused significant suffering, such as personal and family humiliation, as did convictions, which often excluded people from certain jobs and activities.

"A lot of young people's lives get messed up because of arrests over something that is almost impossible to overdose with and where its possible harm is of medium seriousness," Prof Room said.