Cannabis use in patients with early psychosis is a risk factor for relapse, a higher number of re-hospitalizations, and longer length of stay (LOS) in hospital, particularly in black male patients, according to study results published in Psychiatry Research.

Marco Colizzi, MD, of the National Institute for Health Research, Biomedical Research Centre, South London and Maudsley NHS Foundation Trust, and the department of psychosis studies, Institute of Psychiatry, Psychology and Neuroscience, King’s College London, United Kingdom, and colleagues, conducted a chart review study at the Early Intervention Inpatient Unit of the South London and Maudsley NHS Foundation Trust, an inpatient facility that specializes in the care of individuals between the age of 18 and 35 experiencing a first episode of psychosis. All consecutive admissions to the facility in 2010 were included in the study. Patients with suspected or known acute substance intoxication or an organic cause for psychosis were excluded. Patients were followed for 6 years after initial inpatient admission. The investigators used negative binomial regressions to test for an effect of baseline cannabis use on the number of hospital readmissions and LOS during the 6-year follow-up period.

The study included 161 patients, 13 of whom (8.1%) had a second admission and 1 (0.6%) had a third within the same calendar year. Males made up 61% of the study population, whites 28%, black Africans/Caribbeans 50.7%, Asians 13.3%, and mixed ancestry 8%. Information on cannabis use was available for 141 of these patients. The researchers noted that 62.4% of patients had a lifetime history of cannabis use, 61.2% were tobacco users, 64.5% alcohol users, and 38.5% stimulant users. Their initial hospitalization lasted an average of 54.3 days, and over the following 6 years patients had an average of 2.2 hospital readmissions for a total of 197.4 days.

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The analysis suggested that cannabis use significantly predicts the number of hospital readmissions over the 6-year follow-up period (P =.029). However, a further negative binomial regression that adjusted for the use of other psychoactive substances, as well as sociodemographic and other clinical characteristics at baseline, did not find significance for the effect of cannabis on the number of hospital readmissions (P =.072). A significant effect for cannabis use on LOS over the 6-year follow-up was also found (P =.001), and this remained significant even after adjusting for the use of other psychoactive substances (P =.044).

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Other exploratory analyses looked at the effect of gender and ethnicity on the number of hospital readmissions and found a significant interaction between cannabis use and male gender on LOS (P =.034) and between lifetime cannabis use and the number of hospital readmissions over the follow-up period in patients of Afro-Caribbean origin (P =.049).

The investigators suggest that cannabis may have detrimental effects on psychosocial factors such as employment, quality of life, and on physical health, which may affect hospitalizations. They noted as well that experimental studies have shown that the primary psychoactive ingredient in cannabis can induce psychotic symptoms in otherwise healthy individuals.


Colizzi M, Burnett N, Cost R, de Agostini M, Griffin J, Bhattacharyya S. Longitudinal assessment of the effect of cannabis use on hospital readmission rates in early psychosis: a 6-year follow-up in an inpatient cohort [published online August 2, 2018]. Psychiatry Res. doi:10.1016/j.psychres.2018.08