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Use of cannabis and other illicit substances
was associated with an earlier age at onset of psychotic disorders
 
 
  Psychosis has a strong association with substance use.....[in this analysis] Substance users were two years younger at the onset of psychosis compared with nonusers. Age at onset was 2.7 years earlier among cannabis users compared with nonusers......Several birth cohort and population studies have suggested a potentially causal association between cannabis use and psychosis, and cannabis use has been linked to earlier onset of schizophrenia......"This finding is an important breakthrough in our understanding of the relationship between cannabis use and psychosis," they wrote in conclusion. "It raises the question of whether those substance users would still have gone on to develop psychosis a few years later." "The results of this study confirm the need for a renewed public health warning about the potential for cannabis use to bring on psychotic illness," they added.
 
Meta-analysis found that the age at onset of psychosis for cannabis users was 2.70 years younger (standardized mean difference = -0.414) than for nonusers; for those with broadly defined substance use, the age at onset of psychosis was 2.00 years younger (standardized mean difference = -0.315) than for nonusers. Alcohol use was not associated with a significantly earlier age at onset of psychosis. Differences in the proportion of cannabis users in the substance-using group made a significant contribution to the heterogeneity in the effect sizes between studies, confirming an association between cannabis use and earlier mean age at onset of psychotic illness.
 
Conclusions The results of meta-analysis provide evidence for a relationship between cannabis use and earlier onset of psychotic illness, and they support the hypothesis that cannabis use plays a causal role in the development of psychosis in some patients. The results suggest the need for renewed warnings about the potentially harmful effects of cannabis.
 
The results of this study provide strong evidence that reducing cannabis use could delay or even prevent some cases of psychosis. Reducing the use of cannabis could be one of the few ways of altering the outcome of the illness because earlier onset of schizophrenia is associated with a worse prognosis and because other factors associated with age at onset, such as family history and sex, cannot be changed.47 Building on several decades of research, this finding is an important breakthrough in our understanding of the relationship between cannabis use and psychosis. It raises the question of whether those substance users would still have gone on to develop psychosis a few years later. However, even if the onset of psychosis were inevitable, an extra 2 or 3 years of psychosis-free functioning could allow many patients to achieve the important developmental milestones of late adolescence and early adulthood that could lower the long-term disability arising from psychotic disorders. The results of this study confirm the need for a renewed public health warning about the potential for cannabis use to bring on psychotic illness.

 
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Cannabis Use Linked to Earlier Psychosis
 
MedPage Today
Published: February 07, 2011
 
Action Points
 
* Point out that the results of this meta-analysis support a relationship between cannabis use and earlier onset of psychotic illness.
 
* Note that in contrast to cannabis use, alcohol use was not associated with a significantly earlier age at onset of psychosis.
 
Psychotic illness occurs significantly earlier among marijuana users, results of a meta-analysis suggest.
 
Data on more than 22,000 patients with psychosis showed an onset of symptoms almost three years earlier among users of cannabis compared with patients who had no history of substance use.
 
The age of onset also was earlier in cannabis users compared with patients in the more broadly characterized category of substance use, investigators reported online in Archives of General Psychiatry.
 
"The results of this study provide strong evidence that reducing cannabis use could delay or even prevent some cases of psychosis," Matthew Large, MD, of the University of New South Wales in Sydney, Australia, and co-authors wrote in conclusion.
 
"Reducing the use of cannabis could be one of the few ways of altering the outcome of the illness because earlier onset of schizophrenia is associated with a worse prognosis and because other factors associated with age at onset, such as family history and sex, cannot be changed."
 
Psychosis has a strong association with substance use. Patients of mental health facilities have a high prevalence of substance use, which also is more common in patients with schizophrenia compared with the general population, the authors wrote.
 
Several birth cohort and population studies have suggested a potentially causal association between cannabis use and psychosis, and cannabis use has been linked to earlier onset of schizophrenia. However, researchers in the field remain divided over the issue of a causal association, the authors continued.
 
Attempts to confirm an earlier onset of psychosis among cannabis users have been complicated by individual studies' variation in methods used to examine the association. The authors sought to resolve some of the uncertainty by means of meta-analysis.
 
A systematic search of multiple electronic databases yielded 443 potentially relevant publications. The authors whittled the list down to 83 that met their inclusion criteria: All the studies reported age at onset of psychosis among substance users and nonusers.
 
The studies comprised 8,167 substance-using patients and 14,352 patients who had no history of substance use. Although the studies had a wide range of definitions of substance use, the use was considered "clinically significant" in all 83 studies. None of the studies included tobacco in the definition of substance use.
 
The studies included a total of 131 patient samples. Substance use included alcohol in 22 samples, cannabis in 41, and was simply defined as "substance use" in 68 samples.
 
Alcohol use was not significantly associated with earlier age at onset of psychosis.
 
On average, substance users were 1.73 years younger than nonusers were. The effect of substance use on age at onset was greater in women than in men, but not significantly so. Heavy use was associated with earlier age at onset compared with light use and former use, but also not significantly different, the authors reported.
 
Substance users were two years younger at the onset of psychosis compared with nonusers. Age at onset was 2.7 years earlier among cannabis users compared with nonusers.
 
Acknowledging limitations of the study, the authors cited the lack of information on tobacco use and its association with earlier age at onset of psychosis, and the lack of data on individual patients inherent in all meta-analyses.
 
Despite the limitations, the authors said the findings have potentially major clinical and policy implications.
 
"This finding is an important breakthrough in our understanding of the relationship between cannabis use and psychosis," they wrote in conclusion. "It raises the question of whether those substance users would still have gone on to develop psychosis a few years later."
 
"The results of this study confirm the need for a renewed public health warning about the potential for cannabis use to bring on psychotic illness," they added.
 
Primary source: Archives of General Psychiatry
Source reference:
 
Large M, et al "Cannabis use and earlier onset of psychosis. A systematic meta-analysis" Arch Gen Psych 2011; DOI:10.1001/archgenpsychiatry.2011.5.
 
 
 
 
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