Cannabis use and withdrawal and escalation to psychiatric intensive care

Background: Cannabis use is common in people with severe mental illness, and is associated with increased risk of relapse, symptom severity, and violence. Cessation of heavy cannabis use can cause a withdrawal syndrome, which typically peaks after 3-5 days, includes symptoms such as agitation, irritability and aggression, and is more severe in women.
 
When a person with cannabis dependence is admitted to psychiatric hospital, they may develop cannabis withdrawal. Those who develop aggressive or violent behaviour may require management on a psychiatric intensive care unit (PICU). The objective of this study was to assess whether cannabis withdrawal increases the risk of transfer to a PICU after psychiatric admission.
Methods: We used the Clinical Record Interactive Search (CRIS) system to identify individuals receiving inpatient mental healthcare at four London psychiatric hospitals between 2008 and 2023. Any inpatient who was initially admitted to a general psychiatric ward, then transferred to a PICU within 14 days of admission, was included. Their case notes were reviewed to assess cannabis use prior to admission. The primary outcome measure was the proportion of patients transferred to PICU on days 3-5 after admission, tested using a Chi2 test and multivariable analysis
 
Results: Data from 1,560 inpatient episodes involving transfer from a general ward to PICU were included. The mean age at admission was 33.2 years (Standard deviation: 10.3). The majority of cases were male (n=1,009; 64.7%) and the most common primary diagnoses were of a psychotic (n=882; 56.5%) or an affective disorder (n=445; 28.5%). 735 patients (47.1%) were a ‘current user’ of cannabis, 741 (47.5%) were ‘non-users’ (including both ‘past’ and ‘never users’), and 84 (5.4%) had undetermined cannabis use.
 
A greater proportion of ‘current users’ (30.9%) than ‘non-users’ (25.0%) were transferred to PICU on days 3-5 after admission (Odds ratio [OR]=1.34 [95% CI: 1.07 to 1.68], p=0.011). In a multivariable analysis, after adjustment for age, gender, ethnicity, diagnosis, and year of admission, the result was similar (aOR=1.32 [95% CI: 1.04 to 1.69], p=0.025). In a post-hoc analysis, restricted to days 4 and 5, the effect appears to be greater in women (aOR=2.38 [95% CI: 1.47 to 3.83], p<0.001) than men (aOR=1.15 [95% CI: 0.79 to 1.67], p=0.46).
 
Discussion: Cannabis use is associated with an increased risk of transfer to PICU on days 3-5 after admission to hospital, especially in women. This period coincides with the time when a cannabis withdrawal syndrome would be most severe.