Australia and New Zealand has been ranked as the highest users of illegal drugs in the world. According to a study up to 15 per cent of 15 to 64-year-olds have used the drug at least once in the past year.
The study also found that more than 200 million people in the world use illicit drugs, with those in wealthier countries most likely to abuse such substances.
Study co-author Louisa Degenhardt, of the National Drug and Alcohol Research Centre in Australia, said the popularity of illicit drugs was linked to cost and supply.
The study is one of three in a series about addiction to be published in The Lancet.