Young West Australians are the most likely in the nation to have used illicit drugs in the past 12 months, according to a national drugs and alcohol survey.

The report released today by the Australian Institute of Health and Welfare revealed that while some trends were positive, including a reduction of smoking rates and a stabilising of drinking rates, illicit drug use was the worst among the state's youths.

Cannabis use is on the increase in WA.

The 2010 National Drug Strategy Household Survey found that in WA, 39.2 per cent of people aged 18-19 admitted to having used illicit drugs in the past 12 months, significantly higher than the national average of 25.1 per cent for that age group.

The rates were slightly lower for the 20-29 age group, where 34.9 per cent of respondents had used drugs in the past 12 months, compared with 27.5 per cent nationwide.