Legal cannabis dispensaries require proof of age ROBYN BECK/AFP/Getty

Does legalising cannabis make it easier for teenagers to access the drug? The largest study to date suggests not – and it may even have the opposite effect.

In US states that have legalised recreational use of marijuana, fewer teenagers reported taking the drug after the laws were passed.

The world is in the middle of a global reappraisal of the legal status of cannabis. Many regions have legalised or at least decriminalised its possession or trade in some form, including Canada, Spain, Uruguay and many US states.


But critics argue that this might be particularly risky for teenagers, whose developing brains are thought to be more vulnerable to any harms.

Mark Anderson of Montana State University and colleagues looked at existing data from an ongoing anonymous survey of teenagers’ behaviour, which has been carried out every other year since the 1990s. They wanted to see if there were any trends in drug use linked with changes in the law.

The team got results from 27 states and Washington DC that have legalised its use for medical reasons and seven states that have legalised recreational use.

They found there was little difference after medical use was legalised, but after recreational use was permitted, those surveyed were about 8 per cent less likely to say they had used the drug ever in the past month, or to have used it ten times or more.

That might be because when cannabis has become legal, it starts being sold at licensed dispensaries that require proof of age, and these tend to displace criminal drug dealers. “Teens could just use fake IDs or have someone over 21 buy for them, but the point is that it is now more difficult than prior to the law being passed,” says Anderson.

“In certain places where cannabis is illegal, teenagers have reported it is easier to get than alcohol or tobacco because there are no age controls,” says Steve Rolles of Transform, a UK pro-legalisation think-tank.

Journal reference: JAMA Pediatrics, DOI: 10.1001/jamapediatrics.2019.1720