US has 10 million more marijuana users than a decade ago, study finds

Attitudes towards the drug are relaxing, with fewer people perceiving it to be harmful

The drug is thought to be increasingly potent (Rex)

There has been a significant increase in the number of Americans using cannabis, rising from 21.9m in 2002 to 31.9m in 2014. The number of regular users doubled over the same period to 8.4m. This coincides with an increasingly liberal approach to cannabis regulation in several US states.

The authors of a new study, published in The Lancet Psychiatry, also found that people perceived cannabis to be less harmful. This perception seems justified as problems related to cannabis use, such as dependency, remained stable during the study period.

These findings are not what you would expect when cannabis use becomes more popular and is thought to be increasingly potent. This study also contradicts another study, using data over the same period, which found that disorders associated with cannabis use have doubled. So which one should we believe?

The study in The Lancet Psychiatry is problematic as it doesn’t include some of the most marginalised groups, such as the homeless or those in prison. These groups are more likely to use cannabis and develop problems, such as dependency. The absence of these people from the survey might account for the stable numbers of people with a cannabis dependency over the study period. Also, it excludes young people (people under the age of 18) who are more prone to developing cannabis problems than older people.

It can be an inconvenient fact for those lobbying for a more liberal policy approach to cannabis that its use is risky for some. We know that a small number of people use the majority of cannabis consumed. This group is more likely to use a range of substances in addition to cannabis. They are also likely to have a range of additional social problems related to housing, education, employment and crime.

So far, the evidence suggests that those who dabble with cannabis are unlikely to suffer anything worse than feeling nauseous. Unfortunately, there is a small number of people who appear to develop more serious problems as a consequence of their cannabis use, such as mental health issues or dependency. Cannabis has also been implicated in other issues, including poorer educational achievement and doubling the risk of a car crash.

The greatest risk posed by cannabis is that it is still mixed with tobacco by many users. For young new users this can be an introduction to tobacco which leads to dependency and all the harms caused by tobacco use.

An interesting contrast is emerging between the UK and the US. The US has increasingly adopted a more liberal policy approach to cannabis, and this research suggests it has been accompanied by increasing use of the drug. Meanwhile, the UK has continued to prohibit cannabis use – with the government claiming that falling use of the drug in the population justifies their policy position. Both countries are participating in a policy experiment on their populations. Unfortunately, neither country is collecting sufficiently detailed data to be able to draw any reliable conclusions. Both still have the opportunity to rectify this.

Ian Hamilton is a lecturer in mental health at the University of York.

This article was originally published on The Conversation. Read the original article.