Elsevier

Schizophrenia Research

Volume 152, Issue 1, January 2014, Pages 283-288
Schizophrenia Research

A controlled family study of cannabis users with and without psychosis

https://doi.org/10.1016/j.schres.2013.11.014Get rights and content

Abstract

Background

Cannabis is one of the most highly abused illicit drugs in the world. Several studies suggest a link between adolescent cannabis use and schizophrenia. An understanding of this link would have significant implications for legalization of cannabis and its medicinal value. The present study aims to determine whether familial morbid risk for schizophrenia is the crucial factor that underlies the association of adolescent cannabis use with the development of schizophrenia.

Methods

Consecutively obtained probands were recruited into four samples: sample 1: 87 non-psychotic controls with no drug use; sample 2: 84 non-psychotic controls with cannabis use; sample 3: 32 patients with a schizophrenia spectrum psychosis with no drug use; sample 4: 76 patients with schizophrenia spectrum psychosis with cannabis use. All cannabis using subjects used this drug during adolescence, and no other substance, with the exception of alcohol. Structured interviews of probands and family informants were used to obtain diagnostic information about probands and all their known relatives.

Results

There was an increased morbid risk for schizophrenia in relatives of the cannabis using and non-using patient samples compared with their respective non-psychotic control samples (p = .002, p < .001 respectively). There was no significant difference in morbid risk for schizophrenia between relatives of the patients who use or do not use cannabis (p = .43).

Conclusions

The results of the current study suggest that having an increased familial morbid risk for schizophrenia may be the underlying basis for schizophrenia in cannabis users and not cannabis use by itself.

Section snippets

Background

Many studies have shown an association between cannabis use and schizophrenia (Compton et al., 2009, Galvez-Buccollini et al., 2012, Zammit et al., 2002). Compton et al.'s (2009) study and Galvez-Buccollini et al.'s (2012) study both found that cannabis use during adolescence may cause an earlier age of onset of psychosis than would have occurred in the absence of cannabis use. Galvez-Buccollini found a direct association between age of onset of cannabis use and age of onset of psychosis (

Subjects

Subjects came from the New York City metropolitan area where the PI (LED) was a professor in the Department of Psychiatry, New York University, Langone School of Medicine until 2011. On her relocation to Boston and the Department of Psychiatry at Harvard Medical School, the acquisition of subjects was expanded to the Boston area. Eligible subjects in both locations were between the ages of 16 and 40 and consisted of four samples:

  • Sample 1

    Controls with no lifetime history of psychotic illness, cannabis,

Schizophrenia in relatives

Familial aggregation of schizophrenia in first-degree relatives (FDRs) is presented in Table 2. FDR of cannabis using patients had a significantly higher MR for schizophrenia than the cannabis using controls (p = .002). No significant differences in MR for schizophrenia in the FDR of patients who use or do not use cannabis were found (p = .43). There was also no difference in MR for schizophrenia for FDR of controls who use or do not use cannabis (p = .34) (Table 2). There were no significant changes

Discussion

This study aimed to determine whether people who use cannabis during adolescence have a greater risk for developing schizophrenia because they have an increased familial risk for the illness, and thus have a genetic predisposition for developing it regardless of cannabis use. If this is the case, we would expect to find a significantly higher morbid risk for schizophrenia in the relatives of people who develop schizophrenia compared to the relatives of non-schizophrenia controls, regardless of

Role of funding source

None.

Contributors

No other contributors other than those listed in acknowledgments.

Conflict of interest

No co-authors had any conflict of interest.

Acknowledgments

This project was funded by the National Institute of Drug Abuse (R01 DA 021576).

The authors thank Veronica Tomaselli and Melissa Trachtenberg for their work on the grant in ascertainment of subjects and study conduct during their time at New York University School of Medicine and Ashley D. Cameron, BA, and Ariella A. Camera, MS for their help in data collection at the VA Boston Healthcare System. Dr. Richard Rosenthal (Chairman, Department of Psychiatry, St. Luke's Roosevelt Hospital Center,

References (20)

There are more references available in the full text version of this article.

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