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Prevalence of comorbid psychiatric illness and substance misuse in primary care in England and Wales
  1. Martin Frisher1,
  2. Juliet Collins1,
  3. David Millson2,
  4. Ilana Crome3,
  5. Peter Croft4
  1. 1Department of Medicines Management, Keele University, Staffordshire, UK
  2. 2General Practitioner, Leek, UK
  3. 3Academic Psychiatry Unit, Keele University Medical School
  4. 4Primary Care Sciences Research Centre, Keele University
  1. Correspondence to:
 Dr M Frisher
 Department of Medicines Management, Keele University, Staffordshire ST5 5BG, UK;


Study objective: To estimate the annual period prevalence of co-occurring psychiatric illness and substance misuse among patients in primary care.

Design: Analysis of the general practice research database.

Setting: England and Wales, 1993–1998.

Participants: Registered patients at 230 general practices representing 3.1% of the population. A comorbid case was defined as one with both a psychiatric diagnosis and substance misuse diagnosis (not including alcohol or tobacco) within a calendar year. A potentially chronic comorbid case was one that met this definition and, in addition, was treated in subsequent years for either a psychiatric condition or substance misuse.

Main results: The annual period prevalence of comorbidity increased from 50/100 000 patient years of exposure (PYE) to 80/100 000 PYE, an increase of 62% during the study period. Rates of comorbid psychoses, comorbid schizophrenia, and comorbid paranoia increased by 147%, 128%, and 144%. The average age of comorbid cases decreased from 38 years to 34 years. Over 80% of comorbid cases were newly diagnosed in each study year, although many are treated in subsequent years for either psychiatric illness or substance misuse.

Conclusions: This study provides data on the nature and extent of comorbidity in primary care in England and Wales. As the comorbidity rate is increasing by about 10% each year, and as comorbid cases are becoming younger, it is probable that the comorbidity rate will have increased beyond the study end point.

  • PYE, patient years of exposure
  • NPMS, national psychiatric morbidity survey
  • GPRD, general practice research database
  • MHRA, Medicines and Healthcare Products Regulatory Agency
  • ONS, Office of National Statistics
  • OXMIS, Oxford Medical Information Systems
  • OPPCS, Office of Population and Census Statistics
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  • Funding: the study was enabled by a research grant from the Department of Health under the Drug Misuse Research Initiative.

  • Conflicts of interest: none declared.

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