Study finds cannabis linked to increased risks for teenagers

Research that combined the results of 11 studies has found an association (but not a causal link) between cannabis use and ‘low to moderate’ mental health issues and risks of suicide amongst teenagers.

It is still not certain whether cannabis use causes increased risks, or whether people at higher risk are more likely to use cannabis (as self medication or as an escape).

NZ Herald:  New study of 23,000 teen cannabis smokers confirms link to later mental health problems

Cannabis use during adolescence is linked to an increased risk of depression and suicidal behaviour in young adulthood, a new study has found.

But the level of increased risk of depression and suicidal thoughts and attempts found in United States study is only low to moderate. No link was found to anxiety.

The research combines the results of 11 separate studies published over the past 15 years that together included more than 23,000 adolescent cannabis smokers and assessed their mental health when aged 18 to 32. People with prior depression were excluded.

“This review both confirms and reinforces findings from the research literature on the adverse psychological effects of regular cannabis use by mid- to late adolescents,” said Dr Joe Boden, the deputy director of the University of Otago’s Christchurch long-term health and development study.

“The findings of this [US] study further reinforce our concerns about the public health implications of any changes we may choose to make to cannabis laws in New Zealand,” Boden told the Science Media Centre.

Boden has written previously that there is growing evidence that regular or heavy use of cannabis may increase risks of: mental health problems, other forms of illicit drug use, dropping out of school and educational underachievement, and car crashes and injuries.

The new study, published in the Journal of the American Medical Association, does not state how much cannabis the research participants smoked, which is considered a significant omission.

And the study type could not show causal links. British experts have pointed out that as well as cannabis possibly affecting later mental health, it is plausible that people prone to mental health problems are more likely to smoke cannabis.

Dr Lindsey Hines, of the University of Bristol, said it was already known that using cannabis coincided with anxiety, depression and self-harm in teenagers.

While the US study suggested a link between early cannabis use and later issues, “we don’t know if cannabis use as a teenager is causing these adult mental health problems.

“It could be that these behaviours are all due to shared underlying risk factors, such as early adversity or genetics.”

Professor Sir Robin Murray, a psychiatry researcher at King’s College London, said that although the modest risk increase found in the US study was probably real, better-quality studies had found cannabis use increased the risk of schizophrenia-like psychosis more than the risk of depression or anxiety.

He also noted limitations in the US study, including that the researchers had not specified the quantity or type of cannabis smoked.

So this new super-study adds to the information available, but leaves a lot of questions unanswered.

Risks to teenagers of alcohol use is a reason that alcohol sales are restricted to those under 18.

It should also be noted that many teenagers are already using cannabis, so whether cannabis is decriminalised or not needs to consider whether that would increase (or decrease) cannabis use amongst teenagers.

And any drug is potentially harmful to people of any age – as well as being potentially beneficial ib some circumstances.