Young individuals consuming higher-potency cannabis, such as skunk, between ages 16 and 18, are twice as likely to have psychotic experiences from age 19 to 24 compared to those using lower-potency cannabis. That’s according to a new University of Bath study published today in the scientific journal, Addiction.

Previous studies from the Addiction and Mental Health Group at the University of Bath have found that the concentration of THC in cannabis – the main psychoactive component of cannabis – has increased by 14% from 1970 to 2017, meaning today the UK cannabis market is dominated by high-potency cannabis varieties like skunk.

This new study is the first longitudinal examination of early adolescent psychosis measures and detailed cannabis potency.

This data stems from the Children of the 90s study, the most comprehensive research project of its kind. It commenced in Bristol over 30 years ago, gathering information and data from thousands of families across the city.

Nearly 14,000 individuals were recruited into the study from birth, many of which continue to take part in the study to the present day. At ages 16 to 18, participants were asked about recent cannabis use. By age 24, they disclosed their primary cannabis type and any experiences of psychotic experiences such as hallucinations or delusions.

Lead author, Dr Lindsey Hines from the University of Bath Department of Psychology said: “Young people using higher-potency forms of cannabis are twice as likely to have experiences associated with psychosis, such as hallucinations and delusions. Importantly, the young people we asked had not previously reported these experiences before starting their cannabis use. This adds to the evidence that use of higher-potency cannabis may negatively impact mental health.”

This study adds to a wealth of research stemming from the ALSPAC study, which examines various topics from links between medication taken while pregnant and a child’s well-being, to the way social media can lead to self-harm.

Key Findings from this study:

• 6.4% of young people using cannabis had new psychotic experiences, compared to 3.8% of non-users

• After starting to use cannabis, 10.1% of young people using higher-potency cannabis reported new psychotic experiences, compared to 3.8% using lower-potency.

• Those using higher-potency cannabis were more than twice as likely to report new psychotic experiences after starting to use cannabis, compared to those using lower-potency cannabis.

This research adds to the growing body of evidence indicating that high-potency cannabis use is associated with an increased likelihood, and now incidence, of psychotic experiences.

The researchers are now calling for better evidence on the long-term outcomes of use of higher-potency cannabis, and exploration of measures to reduce the potency of cannabis available to young people.

Dr Hines said: ”Cannabis is changing and higher-potency cannabis is increasingly available. These findings show the how important it is to understand the long-term effects of higher-potency use in young people. We need to improve messaging and information available to young people on the impacts of cannabis use in the 21st century.”

The study is published in the scientific journal, Addiction and was funded by The Wellcome Trust.