Whereas in the 1990s it was regular smokers who tended to start using cannabis, it is now often the other way round following changing attitudes to tobacco, with weed smokers moving on to regular cigarettes.
Professor Wayne Hall, from the National Addiction Centre at King’s College London, said that its negative effects should not be underestimated after looking at two decades of data.
“Over the past 20 years, we have seen a large increase in the number of people smoking cannabis,” he said.
“What’s clear is that cannabis, especially when users smoke it regularly and from a young age, can have a detrimental impact on people’s mental health.”
The study, published in the journal Addiction, found that cannabis is less addictive than nicotine, with approximately 9 per cent of users becoming addicted compared to 32 per cent.
But the risk of addiction is higher with teenagers, with one in six who regularly use it becoming dependent and one in ten adults.
For comparison, the figure for heroin is 23 per cent and 15 per cent for alcohol.
Professor Hall, who is also Director of the Centre for Youth Substance Abuse Research at the University of Queensland, said more people are becoming addicted than before.
“It is now difficult to argue that cannabis dependence does not require professional attention,” he added.
“Whilst the mental and physical impact of cannabis dependence is less severe than alcohol or heroin dependence, the number of people who are able to stop smoking cannabis completely following treatment is still very low.”
By Lizzie Dearden, Independent.co.uk