Study claims cannabis use can cause mental health problems

Cannabis use can become addictive, cause mental health problems and lead to hard drug use, according to a new study.

The research, carried out over 20 years by Professor Wayne Hall – a British expert on addiction – found that one in six teenagers who regularly smoke the drug become dependent on it.

It concluded that using the drug while pregnant reduces birth weight, while teenage users do worse at school and are twice as likely to be diagnosed with schizophrenia or report psychotic symptoms in adulthood.

Professor Hall, of King’s College, London, found that one in 10 of all regular users develop dependence on the Class B drug.

His study, published in the journal Addiction, also found that cannabis smokers put themselves at a higher risk of developing chronic bronchitis, while use by middle-aged people “probably” increased the chances of suffering a heart attack.

The report found that evidence has strengthened over the past 20 years that users who stop smoking the drug can suffer withdrawal symptoms which are ``often of sufficient severity to impair everyday functioning''. The most common conditions include anxiety, insomnia, appetite disturbance and depression.

It was noted that the number of cannabis users seeking help to quit or control their habit has increased during the past two decades in Europe, the United States and Australia.

Professor Hall noted that the risk of dependence was ``under-appreciated by lots of users''.

He said: “People ... get caught up, particularly in daily patterns of use, find it difficult to stop or control their use or cease, and continually use the drug despite problems caused by its use.”

The expert acknowledged that cannabis was at the lower scale of risk for addiction to drugs, but warned that the dangers were higher for young people.

“For teenagers, the risk of developing dependence goes up,” he said. “American research suggests it might be as high as one in six amongst young people who might start using cannabis in their mid-teens.

“The particular concern in adolescence are people who get involved in that very heavy pattern of use are much more likely to disengage from school, not complete their education, not engage in further training and drift into affiliating with other people who are similar heavy cannabis users.

“The chances of developing a career or a worthwhile future are often impaired as a consequence.”

Dr Niall Campbell, consultant psychiatrist at the mental health hospital Priory, said: “At Priory we are seeing increasing numbers of patients presenting directly with cannabis addiction and also patients who on further questioning have had considerable difficulties over the years from cannabis.

“As psychiatrists we particularly see patients with serious paranoid psychoses, depressive illnesses and those attempting to self-medicate anxiety states.

“There is still a perceived popular wisdom that cannabis is not addictive. This is not our experience, particularly with the almost universal use of stronger skunk-type cannabis.”

Mark Winstanley, chief executive of the charity Rethink Mental Illness, said: “Too often cannabis is wrongly seen as a safe drug but, as this review shows, there is a clear link with psychosis and schizophrenia, especially for teenagers.

“The common view that smoking cannabis is nothing to get worked up about needs to be challenged more effectively.

“Instead of classifying and re-classifying, Government time and money would be much better spent on educating young people about how smoking cannabis is essentially playing a very real game of Russian roulette with your mental health.”