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J Epidemiol Community Health 2005;59:847-850 doi:10.1136/jech.2004.030833
  • Research report

Substance misuse and psychiatric illness: prospective observational study using the general practice research database

  1. Martin Frisher1,
  2. Ilana Crome2,
  3. John Macleod3,
  4. David Millson4,
  5. Peter Croft5
  1. 1Department of Medicines Management, Keele University, UK
  2. 2Academic Psychiatry Unit, Keele University Medical School, UK
  3. 3Department of Primary Care and General Practice, University of Birmingham, UK
  4. 4Leek Health Centre, UK
  5. 5Primary Care Sciences Research Centre, Keele University
  1. Correspondence to:
 Dr M Frisher
 Department of Medicines Management, Keele University, Staffordshire ST5 5BG, UK; m.frishermema.keele.ac.uk
  • Accepted 21 April 2005

Abstract

Objectives: To quantify the relation between substance misuse and psychiatric illness in the UK general practice population in terms of (a) the relative risk of developing one condition given prior exposure to the other and (b) the proportion of cases of one condition attributable to exposure to the other.

Design: Population based prospective observational study using the general practice research database (GPRD) between 1993 and 1998. The 230 GP practices represent 3.1% of the population.

Setting: England and Wales.

Participants: 1.4 million registered patients of whom 3969 had both substance misuse and psychiatric diagnoses between 1993 and 1998.

Main outcome measures: Relative risk (RR) for subsequent psychiatric illness among participants exposed to substance misuse and RR for subsequent substance misuse among participants exposed to psychiatric illness. Population attributable risk (PAR) of psychiatric illness attributable to substance misuse and of substance misuse attributable to psychiatric illness.

Results: The baseline prevalence of psychiatric illness over the study period was 15% and 0.3% for substance abuse. RR for psychiatric illness for substance misusers compared with non-substance misusers was 1.54 (95% CI 1.47 to 1.62). RR for substance misuse among psychiatric compared with non-psychiatric cases was 2.09 (95% CI 1.99 to 2.22). PAR for psychiatric illness attributable to substance misuse was 0.2%. PAR for substance misuse attributable to psychiatric illness was 14.2%.

Discussion: Only a comparatively small proportion of psychiatric illness seems possibly attributable to substance use whereas a more substantial proportion of substance use seems possibly attributable to psychiatric illness. This study does not support the hypotheses that comorbidity between substance misuse and psychiatric illness is primarily the result of substance misuse or that increasing comorbidity is largely attributable to increasing substance misuse.

Footnotes

  • Funding: the study was enabled by a research grant from the Department of Health under the Drug Misuse Research Initiative. The views expressed in the paper are those of the authors and not the Department of Health who funded the study. JM is funded by a Career Scientist Fellowship from the Department of Health

  • Competing interests: none.

  • Scientific and ethical approval: the study was approved by the GPRD Scientific Ethical Advisory Group (SEAG).

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