Teen weed addiction rises after legalisation

The proportion of teenagers addicted to marijuana rose by a quarter after it was legalised in some American states, a major study has found.

US researchers analysed data on cannabis use and harm from more than 500,000 people aged 12 and older in Colorado, Washington, Alaska and Oregon between 2008 and 2016.

While the proportion of 12 to 17-yearolds who used marijuana remained the same, reports of cannabis use disorder in that age group increased from 2.18 per cent to 2.72 per cent.

Kiwi experts say the finding is worth noting ahead of next year’s referendum on whether New Zealand should legalise cannabis. But more research was needed to prove whether the link was causative.

Cannabis use disorder is when users acknowledge the drug causes them harm, but keep using it anyway.

The research, published in this week, showed people aged 26 and older also had higher rates of cannabis use disorder after legislation, and used cannabis more often when it was legal.

No increases were noted among 18 to 24-year-olds.

Associate professor and head of Massey University’s SHORE & Whariki Research Centre Chris Wilkins said the 25 per cent uplift in the teenage rate of cannabis use disorder was concerning, even though the number of them who were addicted was small.

Many studies indicated cannabis use in adolescence was associated with higher rates of psychosis, drug dependency and other negative outcomes related to education, employment and social welfare.

Psychotherapist Kyle Macdonald cautioned against concluding that similar trends would necessarily be seen in New Zealand if marijuana was legalised here because it would be regulated differently to how it was in some US states.

‘‘For example in Colorado, you’re looking at a largely, market driven, legal but unregulated market, which is not the model that we’re looking for New Zealand,’’ he said.

‘‘One of the concerns of course is that if you legalise it it becomes more accessible [to youth]. But actually if we get the regulation model right, if we get the age restrictions and also the penalties to supplying to [underage people], then actually we potentially can restrict use.’’

Director of the University of Otago’s Christchurch Health and Development Study associate professor Joseph Boden said the increase in teenage cannabis use disorder was notable.

However, as the study was the first to report an increase of cannabis use disorder in teens after legalisation, it was likely too soon to draw any firm conclusions about the relationship between the changes.