People who start using cannabis as teenagers are more likely than drinkers to suffer from mental illness, have relationship problems, and fail to get decent qualifications or jobs, according to a new study by academics.

“Cannabis really does look like the drug of choice for life’s future losers,” says Professor George Patton, who conducted the 10-year study that followed the fortunes of 1,900 schoolchildren until they were 25. “It’s the young people who were using cannabis in their teens who were doing really badly in terms of their mental health. They were also less likely to be working, have qualifications or be in a relationship and more likely to be taking other drugs.”

The 10-year study is the first of its kind to compare drinkers with cannabis users. Almost two-thirds of people had tried cannabis before they turned 18.

Heavy users of the drug were between three and six times more likely to use other drugs, compared with drinkers, less likely to be in a stable relationship and up to three times more likely than drinkers to have dropped out of education or be unemployed.

The results reflect the changing use and attitudes to cannabis by teenagers, according to Professor Patton. “Twenty or 30 years ago, cannabis was uncommonly used by teenagers,” he said. “Alcohol use is still more prevalent, but cannabis use has become widespread in many countries.”

The findings, from Melbourne University’s Centre for Adolescent Heath and published in the current issue of Addiction journal, come after the health risks of cannabis were highlighted by The Independent on Sunday last month.

The debate intensified last week following a report by the newly launched UK Drug Policy Commission, which revealed how Britain remains in the grip of a serious drug problem. It says that one in four people in their late twenties have tried heroin or cocaine at least once and that nearly half of all young people have used cannabis. Britain’s drug addiction rate is more than twice that of France, Germany, Sweden or Holland.

More than 22,000 people needed treatment for cannabis use in Britain last year. The number of emergency hospital admissions due to cannabis has almost doubled in five years - from 581 in 2001 to nearly 1,000 last year. Britain’s teenagers are most at risk as the drug acts on the developing brain, according to leading experts.

Concerns have spread to some of Britain’s top teachers amid worries that it is joints and not cigarettes that are now most likely to be smoked during breaks.

In response, Dr Anthony Seldon, master of Wellington College, Berkshire, held a conference on Friday. Dozens of the country’s top schools, including Harrow, Bedales, Kingston Grammar and Uppingham, met senior police officers and experts from drugs and mental health charities.

“Most schools are in a muddle about how to deal with drugs,” said Dr Seldon. “We know the problem is growing and about the new evidence linking cannabis to schizophrenia. But the absence of clear guidelines on what to do, or a clear message from the Government that cannabis is dangerous, does not help us.”

But drug reform organisation Transform says that legalisation of cannabis is the way forward. A spokesman said: “It is precisely because drugs are dangerous that they need to be appropriately regulated rather than be left in the hands of criminal profiteers.”

By Jonathan Owen