Increase in psychotic symptoms predicts relapse to cannabis use
Aug 9, 2006 - 12:40:37 PM

There may be a two-way relationship between cannabis use and psychosis, according to a new study from Australia. Published in the August issue of the British Journal of Psychiatry, the study found that more frequent cannabis use was associated with a higher risk of psychotic relapse, and more severe psychotic symptoms were associated with increased risk of cannabis relapse.

This was the first prospective study to explore systematically the relationship between cannabis use and psychotic symptoms and relapse, relative to other risk factors, over a 6-month period using highly sensitive measures and frequent follow-up.

At the start of the study, 84 people with recent-onset psychosis were assessed, and 81 were followed up weekly for 6 months, using telephone and face-to-face interviews.

Over 70% of the participants were male, and the average age was 24. Nearly 80% were single and 76% were on disability/unemployment benefits. The average duration of untreated psychosis was 118 days.

It was found that the risk of psychotic relapse increased by approximately 6.4% with each additional day of cannabis use within a 1-week period.

There was a high rate of cannabis relapse, with 61% of participants increasing their cannabis use to a level that met the definition of a cannabis relapse.

After taking into account medication adherence, life stress, other substance use and age at onset of regular cannabis use, psychotic symptom severity was predictive of a cannabis relapse.

These results are consistent with the reports of participants that cannabis use is one way of coping with an increase in positive psychotic symptoms, such as delusions and hallucinations.

The severity of symptoms of depression and anxiety at the start of the study also emerged as a significant predictor of time to psychotic relapse (but not to a relapse in cannabis use), although this finding needs further investigation.

The authors of the study comment that the use of repeated- measures design to obtain a detailed picture of symptoms, medication, stress and substance use provides the best evidence to date for a strong association between cannabis use and psychotic relapse.

Although further research is needed, this study suggests that when compared with the effect of cannabis use, other risk factors for relapse – such as duration of untreated psychosis, adherence to medication and chronic and acute stress – have less impact on the relapse process.

The findings of this study highlight the need for early intervention programmes to target both cannabis use and psychotic symptom severity in young people.

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