Adolescents are more than three times more likely than adults to develop a cannabis addiction, but they may not be at increased risk of other mental health problems associated with the drug, according to a new study led by UCL and King’s College London researchers.

The study, published today in the Journal of Psychopharmacology, discovered that adolescents who used cannabis were no more likely than adults to have higher levels of subclinical depression or anxiety, nor were they more vulnerable to the associations with psychotic-like symptoms.

A study finds that adolescents are more vulnerable to cannabis addiction but not to other mental health risks.

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

“There is a lot of concern about how the developing teenage brain might be more vulnerable to the long-term effects of cannabis,” said lead author Dr. Will Lawn (UCL Clinical Psychopharmacology Unit and Institute of Psychiatry, Psychology, and Neuroscience at King’s College London).

“Cannabis addiction is a real problem that teenagers should be aware of because they appear to be far more susceptible than adults.

“However, the impact of cannabis use during adolescence on cognitive performance or depression and anxiety may be weaker than previously thought.

“However, we also replicated previous research that suggests that becoming addicted to cannabis may worsen the severity of subclinical mental health symptoms. Because adolescents are more likely than adults to experience mental health problems, they should be actively discouraged from using cannabis on a regular basis.”

The findings in both papers are from the CannTeen study, which is funded by the Medical Research Council and compares the effects of regular cannabis use among adolescents and adults, as well as age-matched controls (non-users of cannabis), a completely novel design.

The study included 274 participants, including 76 adolescents (aged 16 and 17) who used cannabis one to seven days per week, as well as a similar number of adult (aged 26-29) users and adolescent and adult control (comparison) participants, who all answered questions about their cannabis use over the previous 12 weeks and completed questionnaires commonly used to assess symptoms of mental illness. The cannabis users in the study used it four times per week on average. The adolescent and adult users were also carefully matched in terms of gender, ethnicity, and cannabis type and strength.

The researchers discovered that adolescent cannabis users were three and a half times more likely than adult users to develop severe ‘cannabis use disorder’ (addiction), a finding that is consistent with previous evidence from different study designs. Cravings, cannabis use contributing to failures in school or work, heightened tolerance, withdrawal, interpersonal problems caused or exacerbated by cannabis use, or intending to cut back without success are all symptoms of cannabis use disorder. The researchers discovered that half of the adolescent cannabis users studied have six or more cannabis use disorder symptoms, indicating a severe cannabis use disorder.

Previous research has found that 9-22 percent of people who try the drug develop cannabis use disorder, and that risk is higher for those who try it at a younger age. Adolescents are at a higher risk of cannabis addiction, which has now been robustly replicated.

Adolescents may be more vulnerable to cannabis addiction due to factors such as increased disruption in relationships with parents and teachers, a hyper-plastic (malleable) brain and developing endocannabinoid system (the part of the nervous system that THC in cannabis acts upon), and an evolving sense of identity and shifting social life, according to the researchers.

Adolescent users were more likely to develop psychotic-like symptoms than adult users or adolescent non-users, but the analysis revealed that this is because all adolescents, and all cannabis users, are more likely to newly develop psychotic-like symptoms, rather than cannabis affecting teenagers differently than adults. In other words, there was no adolescent vulnerability because the increased risk of psychotic-like symptoms was an additive effect (of two previously identified risk factors for psychotic-like symptoms, cannabis use and adolescent age), rather than an interaction between age and cannabis use.

The researchers say their findings support previous evidence that cannabis use may increase the risk of developing a psychotic disorder like schizophrenia, but they caution that their study did not look into the risk of clinical psychosis or schizophrenia.

The researchers discovered that neither adolescent nor adult cannabis users were more likely than non-users to develop depression or anxiety symptoms. Only adolescents with severe cannabis use disorder experienced worse mental health symptoms, but the researchers warn that the small sample size for this group limits their confidence in this finding.

A separate study published in Psychopharmacology discovered that cannabis users had no increased risk of impaired working memory or impulsivity. Cannabis users were more likely to have poor verbal memory (forgetting what was said to them); this effect was observed in both adults and teenagers, indicating that there was no adolescent vulnerability. However, the researchers warn that cannabis use could have an impact on school performance during a critical developmental stage.

The researchers emphasize that their findings were cross-sectional (only looking at one point in time), and that longitudinal analyses of how their participants changed over time are still ongoing.

Professor Val Curran (UCL Clinical Psychopharmacology Unit, UCL Psychology & Language Sciences) is the study’s senior author “Our findings suggest that schools should teach students more about the dangers of cannabis addiction, which has been overlooked in drug education. Addiction to cannabis is a serious issue in and of itself, but it can also increase the likelihood of other mental health issues. Teenagers should be made aware of their increased risk of addiction.”

Source: Materials provided by University College London.

Reference:  DOI: 10.1177/02698811221108956

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