MedWire News: Cannabis use is associated with an earlier age at disease onset in patients with schizophrenia, as well as with a greater number of hospital admissions, researchers report.

Daniel van Dijk (General Mental Health Institute 'Duin en Bosch', Castricum, the Netherlands) and colleagues advise that "patients with schizophrenia should be informed about the possible effects of cannabis and trained not to use cannabis or to reduce their cannabis use as much as possible."

The team studied the prevalence of cannabis use and associations with illness course over 12 months among 145 men (aged 18‑65 years) with schizophrenia living in the Netherlands.

All of the participants were assessed for cannabis use using the Cannabis Assessment Scale.

The researchers found that patients who used cannabis (46.9%) had a significantly earlier age at schizophrenia onset compared with those who did not use the drug, at 18.3 versus 20.8 years, respectively.

Cannabis users also had a greater mean number of hospital admissions, indicating a greater risk for relapse, over the 12-month follow-up period than did nonusers, at 1.2 versus 0.7 admissions, as well as a greater mean number of hospitalization days, at 201.0 versus 150.4.

The results remained significant after accounting for possible confounding factors, including the use of other illegal substances and alcohol.

However, there were no significant differences between cannabis users and nonusers regarding scores on the Positive and Negative Syndrome Scale or the Lancashire Quality of Life Scale, European version.

The team also notes that there was no significant association between the severity of daily cannabis use and psychopathology measures.

Writing in Schizophrenia Research, van Dijk and team conclude: "The current prospective study… confirms the findings of previous studies showing that in patients suffering from schizophrenia cannabis use is associated with an earlier age at onset.

"The actual use of cannabis is also associated with a negative effect on the course of the illness with more frequent relapses and subsequent hospitalization resulting in a substantial increase in the total number of days hospitalized."

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