Teens, young adults, pregnant women and drivers should avoid cannabis, experts advise

Cannabis should be avoided during the teenage years and early adulthood as well as in pregnancy and before and after driving, a group of experts has advised after an in-depth review of the evidence.

People prone to or with mental health disorders should also stay clear, the international team which included UK researchers said, after reviewing studies which found an increased risk of psychosis linked to its use.

The review, the largest of its kind, considered 101 meta-analyses published since 2002 and found specifically that cannabis was associated with psychosis in adolescents and with psychosis relapse in people already diagnosed with a psychotic disorder.

This association was particularly concerning given the overlap of when young people start to try cannabis, as this coincides with the peak age of the onset of mental health disorders, they noted.

An association between cannabis and general psychiatric symptoms, including depression and mania, as well as detrimental effects on memory, verbal and visual recall, was also found in the review with varying strengths of evidence.

But cannabidiol is effective in people with epilepsy, and cannabis-based medicines can help people with multiple sclerosis, chronic pain, inflammatory bowel disease, and in palliative care, they concluded in The BMJ.

Across different populations, there is also evidence suggesting a link between cannabis use and car accidents.

For pregnant women, there was also a convincing association between cannabis use and risk of having a small, low birth weight baby, they reported.

But they stressed that most outcomes they looked at have been seen in observational studies, trials with low levels of certainty or the findings have not been significant.

And the research had been limited by factors such as differences in the cannabis content of products, and that not all individuals will experience the same effects of cannabis on their mental health and cognition as well as the fact that randomised trials might not be representative of the real-world population. 

‘Convincing or converging evidence supports that cannabis use is associated with poor mental health and cognition, increased the risk of car crashes, and can have detrimental effects on offspring if used during pregnancy,’ the researchers concluded.

‘Cannabis use should be avoided in adolescents and young adults (when neurodevelopment is still occurring), when most mental health disorders have onset and cognition is paramount for optimising academic performance and learning, as well as in pregnant women and drivers.’