A collaborative study between University College London (UCL) and King’s College London has discovered that adolescents are over three times more likely to develop cannabis addiction than adults.
The investigation identified that although younger users were significantly more likely to develop cannabis addiction – also known as cannabis use disorder – there was no association found between cannabis use and an increased risk of mental health conditions.
The research revealed that adolescent cannabis users may not have higher levels of subclinical depression or anxiety than adults and were not more vulnerable to psychotic-like symptoms. The findings reinforce a previous study from the team that identified that adolescents were not more vulnerable to associations between cannabis addiction and cognitive impairment.
Dr Will Lawn, the lead author of the study from the UCL Clinical Psychopharmacology Unit and Institute of Psychiatry, commented: “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.
“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.
“But we also replicated previous work that if someone becomes addicted to cannabis, that may increase the severity of subclinical mental health symptoms. Given adolescents are also at a greater risk of experiencing difficulties with mental health than adults, they should be proactively discouraged from regular cannabis use.”
What is cannabis use disorder?
Cannabis use disorder is characterised by symptoms such as cannabis cravings, use that impacts school or work performance, a heightened tolerance to the drug, withdrawal symptoms, problems in personal relationships caused by or worsened by cannabis use, or failed attempts to quit cannabis.
Analysing chronic cannabis use
The results from both investigations are derived from the Medical Research Council-funded CannTeen study, which analysed the effects of regular cannabis use on adolescents and adults. The team compared the results to age-matched control of individuals who do not use cannabis.
The study comprised 274 participants, 76 of which were adolescents aged between 16 and 17 who used cannabis one day per week. The other participants included a similar number of adult cannabis users aged 26 to 29 and teenage and adult controls.
The cannabis users in the study used the drug four times per week on average and were carefully matched on gender, ethnicity, and type and strength of cannabis. The participants answered questions about their cannabis use during the last 12 weeks and questionnaires employed to assess symptoms of mental ill health.
Adolescent’s risk of cannabis addiction
The results illuminated that adolescent users were three and a half times more likely to develop cannabis addiction than adults and that 50% of teenagers who use cannabis have six or more cannabis disorder symptoms that define them as having severe cannabis use disorder.
Previous studies suggested that people of any age who use cannabis are between 9-22% more likely to become addicted to cannabis, with the risk being highest for those who tried cannabis at a younger age.
The team hypothesise that adolescents may be more vulnerable to cannabis addiction than adults because of factors such as disruptions to relationships, a hyper-plastic (malleable) brain, a developing endocannabinoid system, and an evolving sense of identity and social life.
Mental health impacts
The study identified that adolescent cannabis users did not have an increased vulnerability for developing psychotic-like symptoms than adults. The results also demonstrated that teenage and adult users were not more likely to develop symptoms of depression or anxiety, with only adults with severe cannabis addiction having worse mental health symptoms.
In contrast, the team’s other study discovered that cannabis users were more likely to have impaired working memory, impulsivity, and verbal memory. This was displayed among adults and teenagers, meaning there was no increased adolescent vulnerability.
The researchers explained that due to the findings of the study being cross-sectional, a longitudinal analysis would need to be performed to see how cannabis users develop over time.
Professor Val Curran, the senior author of the study from the UCL Clinical Psychopharmacology Unit, concluded: “Our findings suggest that schools should be teaching pupils more about the risk of addiction to cannabis, which has been neglected in drugs education. Becoming addicted to cannabis is a serious problem in itself, but it can also increase the likelihood of other mental health problems. Teenagers should therefore be informed of their greater risk of addiction.”
