King's College London

The research, published in JAMA Psychiatry, highlights the often-overlooked effects of CWS compared to withdrawal from other substances which are already routinely diagnosed and treated. Researchers suggest that improved assessment and treatment of patients for CWS could have an immediate impact on reducing the number of people being transferred to PICU.

CWS typically leaves a user feeling agitated, irritable and potentially aggressive, with symptoms peaking three to five days after last use. These symptoms can be exacerbated in people with mental illness. Researchers wanted to establish if there was an association between CWS and admission to PICU following admission to a standard psychiatric ward.

They obtained anonymised patient data from the South London and Maudsley NHS Foundation Trust’s four PICUs. They then reviewed patient records to clarify if they were using cannabis prior to admission.

They found that, of the 1236 cases of a patient being transferred to PICU following admission to general ward, a greater proportion of cannabis users (31 per cent) than non-cannabis users (24 per cent) were transferred during the cannabis withdrawal risk period (3-5 days after admission). The effect was particularly prominent in women, who are known to experience more severe cannabis withdrawal symptoms.

Dr Edward Chesney, Academic Clinical Lecturer at the IoPPN, Resident Psychiatrist at South London and Maudsley NHS Foundation Trust, and the study’s senior author said, "Our study found a clear association between CWS and an increased risk of being transferred to PICU in patients with mental illness. While it would require further research to confirm, we could see an immediate impact on the number of transfers to PICU by screening and treating cannabis users with medications to reduce the symptoms of cannabis withdrawal. This would improve patient welfare, ward safety, and ease pressure on overstretched PICUs."

Dr Aliyah Malik, the first author of the study, who works as a Foundation Doctor at Somerset NHS Foundation Trust said: “There is some evidence from clinical trials that cannabis-based medicines can be used to treat CWS. If you slowly reduce the dose over a week, you can reduce symptoms like insomnia and agitation. These trials were completed in otherwise healthy people, so we need to make sure that this approach is also safe in people with acute psychiatric conditions before putting it into clinical practice.”

This work was supported by funding from Maudsley Charity and the National Institute for Health and Care Research Maudsley Biomedical Research Centre.

Cannabis Withdrawal and Psychiatric Intensive Care (DOI10.1001/jamapsychiatry.2025.1216) (Aliyah Mailk, Hitesh Shetty, Dominic Oliver, Thomas Reilly, Marta Di Forti, Philip McGuire, Edward Chesney) was published in JAMA Psychiatry.