Scientists studying the effects of cannabis on the developing teenage brain have found adolescents may be more vulnerable to ‘addiction’ than adults, but are no more likely to develop mental health problems related to the drug.

Researchers at King’s College London and UCL found teenagers who used cannabis were no more likely to have higher levels of subclinical depression or anxiety than adults who did so, nor were they more vulnerable to psychotic-like symptoms.

The team studied 76 adolescents aged 16 and 17 who used cannabis one to seven days per week, a similar number of adult users aged 26 to 29, and non-user controls for each group. 

All 274 participants answered questions about their cannabis use over the last 12 weeks and responded to questionnaires commonly used to assess mental health. On average, the cannabis groups used the drug four times per week. They were carefully matched for gender, ethnicity and type/strength of cannabis.

The researchers found adolescent users were 3.5 times more likely to develop severe ‘cannabis use disorder’ than adult users, as defined by symptoms such as cravings, use contributing to failures in school or work, heightened tolerance, withdrawal, interpersonal problems caused or exacerbated by use, or intending to cut back without success. 

The researchers found that 50% of the teenage users had six or more cannabis use disorder symptoms, qualifying as severe.

Lead author Dr Will Lawn said: “There is a lot of concern about how the developing teenage brain might be more vulnerable to the long-term effects of cannabis, but we did not find evidence to support this general claim.”

Dr Will Lawn

He warned: “Cannabis addiction is a real issue that teenagers should be aware of, as they appear to be much more vulnerable to it than adults. 

“On the other hand, the impact that cannabis use has during adolescence on cognitive performance or on depression and anxiety may be weaker than hypothesised.”

The researchers said adolescents may be more vulnerable to cannabis addiction because of increased disruption to relationships with parents and teachers, a hyper-plastic (malleable) brain and developing endocannabinoid system, and an evolving sense of identity and shifting social life.

They warned that the findings are cross-sectional (only looking at one time point), and that longitudinal analysis of how participants changed over time is ongoing.

The findings, published in the Journal of Psychopharmacology, build on a separate study by the same team that found adolescents were not more vulnerable to associations between chronic cannabis use and cognitive impairment.

Both papers come from the CannTeen study, funded by the UK’s Medical Research Council, which compares the effects of regular cannabis use among adolescents and adults, and to age-matched control groups.

Meanwhile, Indiana University neuroscientists recently received more than US$2 million from the National Institute on Drug Abuse to use mice to better understand the impact of cannabis use during adolescence.

Prior to launching Cannabiz, Martin was co-founder and CEO of Asia-Pac’s leading B2B media and marketing information brand Mumbrella, overseeing its sale to Diversified Communications in 2017. A journalist...

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