MedWire News: There is a significant and positive dose-response relationship between cannabis use and risk for psychiatric hospitalization, study results suggest.
The researchers also found that cannabis use before the age of 12 years is significantly associated with increased risk for psychiatric hospitalization in later life.
Writing in the journal Acta Psychiatrica Scandinavica, Christian Schubart (University Medical Centre Utrecht, The Netherlands) and team explain: "In the last decade, increased attention has been given to the psychiatric effects of cannabis use."
They add: "It is now clear that cannabis use is associated with psychotic disorders, and although the debate on causality is ongoing, an argument can be made that the public should be warned of this danger."
To investigate whether cannabis use is associated with an increased risk for psychiatric hospitalization, the team studied the internet questionnaire responses of 17,698 individuals aged an average of 22 years.
Responders were asked whether they had ever used cannabis and, if so, at what age they had started using the drug, and the amount of money they spent on cannabis each week over the past month. They were also asked whether they had ever been admitted to a psychiatric ward.
Incidental cannabis used was defined as spending less than €3 (US$4.39) per week on the drug, while heavy use was defined as spending more than €25 ($36.63) per week.
In total, 11,856 responders reported using cannabis while 5842 had never used the drug. Of these, 3.4% and 1.1%, respectively, had been admitted to a psychiatric ward at least once.
The researchers found that the risk for psychiatric hospitalization increased with increasing levels of cannabis use. Indeed, after adjustment for age, gender, and level of education, responders who were incidental cannabis users had a 1.6-fold increased risk for psychiatric hospitalization, compared with individuals who had never used the drug, while those who were heavy users had a 6.2-fold increased risk.
The team also found that responders who started using cannabis before the age of 12 years were 4.8 times more likely to have a history of psychiatric hospitalization than those who had started using the drug after the age of 15 years, after adjustment for age, gender, level of education, and weekly amount of use.
Schubart and team conclude: "The current results are clinically meaningful irrespective of the question of causality because they suggest that early or heavy cannabis use are clearly associated with the development of major psychiatric illness (requiring intensive in-patient treatment)."
They add: "Although the underlying causal pathway remains unclear, early and heavy use of cannabis are each associated with poor mental health in its users and thus with significant medical and economic costs for society."
MedWire (www.medwire-news.md) is an independent clinical news service provided by Springer Healthcare Limited. © Springer Healthcare Ltd; 2011
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