Importance: Cannabis use is common in people with severe mental illness and its adverse effects on outcomes are well established. However, adverse outcomes may also result from cannabis withdrawal syndrome (CWS). CWS includes symptoms such as agitation, irritability, and aggression, and typically peaks after 3 to 5 days of abstinence.

Question: Does cannabis withdrawal increase the risk of admission to psychiatric intensive care?

Findings: In psychiatric inpatients, cannabis use prior to admission was associated with an increased risk of admission to intensive care. This risk was particularly elevated 3 to 5 days after presentation to hospital, a period associated with the peak severity of cannabis withdrawal syndrome.

Meaning: In people with psychiatric disorders, cannabis withdrawal may occur shortly after hospital admission and exacerbate their mental state.