August 27, 2025

Why do people first use cannabis and does that influence later health outcomes?

People start using cannabis for a variety of reasons, such as self-medicating for physical or mental discomfort, because friends and family members use it, for fun, or simply out of boredom. In the largest study of its kind, researchers have analysed data from 3,389 cannabis users to investigate their reasons for first using cannabis, and then their subsequent pattern of use, weekly THC consumption, and any symptoms of paranoia, anxiety or depression they experience.

As laws around medicinal and recreational cannabis use continue to change worldwide, this study sheds light into whether there are specific subgroups of individuals who may be more at risk of negative outcomes and whether reasons for first use could help identify individuals who may benefit from monitoring or interventions for their mental health. This work was published BMJ Mental Health.

Using the same dataset, the authors have new findings – published in Psychological Medicine – on the role cannabis may play in the relationship between childhood trauma and paranoia which they also presented at this briefing.

Speakers included:

Professor Marta di Forti, Professor of Drug use, Genetics and Psychosis, Department of Social, Genetic & Developmental Psychiatry at the Institute of Psychiatry, Psychology & Neuroscience (IoPPN), and Honorary Consultant Adult Psychiatrist, Lambeth EI Community team, South London and Maudsley NHS Foundation Trust.

Prof Sir Robin Murray, Professor of Psychiatric Research, Institute of Psychiatry, Psychology & Neuroscience (IoPPN)

Dr Giulia Trotta, Research Assistant, Department of Social, Genetic & Developmental Psychiatry at the Institute of Psychiatry, Psychology & Neuroscience (IoPPN)

This Briefing was accompanied by an SMC Roundup of comments.