The prevalence of this pattern of substance use increased with age, the study found, prompting the authors to raise concerns that these behaviours are likely to worsen both mental and physical health.

The evidence suggests that an early start on substance misuse increases the likelihood of mental ill health, and vice versa.

The authors base their findings on more than 2000 12 to 30 year olds, who were part of the national mental health headspace programme in Sydney, Australia.

Those seeking help for a wide range of mental health issues provided information on their weekly consumption of alcohol, tobacco and cannabis, with 500 giving more detailed information on their pattern of alcohol consumption.

One in eight (12%) young teens aged 12 to 17 drank alcohol at least once a week, as did almost four out of 10 (39%) 18-19 year olds, and almost half of those aged 20 to 30.

Those in the youngest age group were twice as likely to say they drank alcohol every week as their peers in the general population.

And a significant proportion of those who provided more detailed information on their alcohol consumption were "risky" drinkers, with almost half of those with bipolar disorder falling into this category.

Some 7% of young teens said they used cannabis at least once a week. The equivalent figures for the other two age groups were 14% and 18%, respectively.

Furthermore, those in the two younger age groups were more likely to smoke cannabis every day than they were to drink alcohol (3.6% vs 1.5% and 8.8% vs 6.0%, respectively).

Almost one in four (23%) young teens admitted to smoking cigarettes daily, as did one in three (36%) of older teens and four out of 10 (41%) of those aged 20 to 30.

The average age at which these patterns started was 15. And those who used any or all of the three substances were more likely to be male, older, and to have psychotic or bipolar disorders.

The authors point out that people with mental health issues are significantly more likely to develop serious health problems and to die early.

"Given the comorbidity with significant mental health problems, these patterns of substance use are likely to contribute to increased risk of poor physical and/or mental health outcomes," write the authors, adding that the patterns they found among the 12 to 17 year olds were "particularly notable."

Traditionally, mental health and drug and alcohol services have tended to be separate entities, but it might be more helpful to bring them together, suggest the authors.