Teens who use high-THC cannabis are twice as likely to experience psychotic episodes

Young adults aged 16 to 18 who use high-potency cannabis such as "skunk" are twice as likely to experience psychotic symptoms between the ages of 19 and 24 compared to those who use low-potency cannabis. This is according to a new study from the University of Bath, published in the scientific journal "Addiction".

Previous research from the Addiction and Mental Health Group at the University of Bath has shown that the concentration of THC (delta-9-tetrahydrocannabinol) in cannabis - the main psychoactive component of cannabis - increased by 14% between 1970 and 2017. This means that the UK cannabis market is now dominated by high-potency strains such as 'skunk'.

This new study is the first longitudinal study to examine measures of early adolescent psychosis and to analyse cannabis potency in detail.

These findings are based on the Children of the 90s study, the largest research project of its kind. It began in Bristol more than 30 years ago, collecting information and data from thousands of families across the city.

The study included almost 14,000 people from birth, many of whom continue to take part in the study today. Between the ages of 16 and 18, participants were asked about their recent cannabis use. By the age of 24, they reported their main type of cannabis and any psychotic experiences, such as hallucinations or delusions.

Lead author Dr Lindsay Hines, from the University of Bath’s Department of Psychology, said: “Young people who use high-potency cannabis are twice as likely to experience psychosis-related experiences, such as hallucinations and delusions. Importantly, the young people we asked had not previously reported such experiences before starting to use cannabis. This confirms that high-potency cannabis use may have negative impacts on mental health."

This study adds to the extensive research being conducted as part of the ALSPAC study, which covers topics ranging from the relationship between medication use during pregnancy and child well-being to the impact of social media on suicide.

The key findings of this study are:

• 6.4% of young people who use cannabis had new psychotic experiences, compared with 3.8% of non-users.
• After initiating cannabis use, 10.1% of young people who use high-potency cannabis reported new psychotic experiences, compared with 3.8% of low-potency users.
• Those who used high-potency cannabis were more than twice as likely to report new psychotic experiences after initiating cannabis use, compared with low-potency users.

This study adds to the growing evidence that high-potency cannabis use is associated with an increased likelihood and now frequency of psychotic experiences.

The researchers call for better data on the long-term effects of high-potency cannabis use and for interventions to reduce the potency of cannabis available to young people.

Dr Hines said: “Cannabis is changing and high-potency cannabis is becoming more widely available. These findings highlight how important it is to understand the long-term effects of high-potency cannabis use in young people. We need to improve the way we communicate and inform young people about the impact of cannabis use in the 21st century.”