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
Statistics from Altmetric.com
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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