IS THERE A CAUSAL RELATIONSHIP BETWEEN SUBSTANCE ABUSE AND PSYCHIATRIC ILLNESS?

1. IS THERE A CAUSAL RELATIONSHIP BETWEEN SUBSTANCE ABUSE AND PSYCHIATRIC ILLNESS? Dr Martin Frisher Department of Medicines Management Keele University, Staffordshire, UK m.frisher@mema.keele.ac.uk Manchester, Tuesday 24th November 2005

2. UK Department of HealthComorbidity in Primary Care • Study 1: Estimate the occurrence of comorbidity in primary care in England and Wales. • Study 2: Analyse the time sequence between mono and dual diagnosis. • Study 3: Compare health care utilisation by mono, comorbid and control patients. • Study 4: Confirm whether secondary care diagnoses are recorded in primary care.

3. Papers from the study Frisher M, Collins C, Millson D, Crome I, Croft P. Prevalence of comorbid psychiatric illness and substance misuse in primary care in England and Wales Journal of Epidemiology and Community Health 2004; 58:1036-1041 Frisher M, Crome I, Macleod J, Millson D, Croft P. Substance misuse and psychiatric illness: prospective observational study using the general practice research database. Journal of Epidemiology and Community Health 2005; 59:847–850

4. First presentation to health service • Addicts’ mental illness being being ignored? George Harrison’s attacker Michael Abram’s schizophrenia was not diagnosed - because of heroin abuse? • On the other hand, among psychiatric patients…..“addiction being ignored” “Urgent action is needed to help mentally-ill people who are addicted to drink or drugs, an influential group of MPs has warned”. (All-Party Parliamentary Drugs Misuse Group, 2000)

5. Comorbidity: US Research • 50% of schizophrenic patients have substance misuse disorder • Such co-morbidity is associated with: heavy use of psychiatric inpatient care, poor treatment compliance, poor prognosis and high offending rates • Services combining psychiatric and substance misuse treatments may be more effective than management by separate services

6. Pathways to Comorbidity Crome I. (1999). Substance misuse and psychiatric comorbidity: towards improved service provision. Drugs: Education, Prevention and Policy. 6 (2) pp151-174

7. Type of Comorbidity Study • Prevalence • General population, primary care, specialist services • Development of comorbidity • Clinical, epidemiological • Treatment • Standard or specialised

8. Studying Co-morbidity using the GPRD • Data collected from about 1.8 million patients (230/370 practices) • 258 substance misuse diagnoses and 1,693 psychiatric diagnoses (based on ICD 9 and Read Codes)

9. Classification of Psychiatric and Substance Abuse Diagnoses

10. Patients included in the study

11. Changes in Psychiatric Illness and Substance Abuse Use Published data, Extrapolated to E&W

12. Annual Comorbidity Prevalence Rate

13. Incident and Prevalent Cases

14. Annual comorbidity rates per 100,000 PYE by ageband and gender

15. Rate of psychiatric comorbidity per 100,000 PYEPercentage change in psychiatric comorbidity 1993-1998

16. Illicit Drug Use and Mental Health ‘Evidence establishes clear link between use of cannabis and mental health’ BMJ Editorial 2002

17. Cannabis and Mental Health ‘Cannabis use does not appear to be causally related to the incidence of schizophrenia’ ‘It may precipitate disorders in persons who are vulnerable to developing psychosis’ Degenhardt et al Drug and Alcohol Dependence 2003

18. The move to causality • Use of cannabis increases the risk of schizophrenia and depression but baseline psychiatric illness is not associated with an elevated risk of substance use (Rey J and Tennant C. Cannabis and Mental Health. BMJ 2002; 325: 1183-4 2002). • “Use of cannabis will contribute to more episodes or new cases of (psychiatric) illness”(assumes that cannabis use is increasing and/or) the level of cannabis use among users is increasing). • “Surprising that, given this association, there does not appear to increasing incidence of schizophrenia in the population”.

19. Does Substance Misuse Cause Mental Illness?Consensus Pre BMJ • Substance misuse can have a negative impact upon the course of psychotic disorders and can exacerbate symptoms • Some substances, particularly alcohol, cannabinoids, hallucinogens and stimulants can produce psychotic symptoms directly without coincidental mental illness. • Although these substances may trigger psychotic disorders amongst people with a predisposition, the existence of any stronger causal relationship remains controversial.

20. Is the evidence clear? • Some reports suggest cannabis exacerbates symptoms of schizophrenia, but two clinical studies suggest cannabis use alleviates symptoms. • Cannabis use is not associated with the development of psychosis in an 'ultra' high-risk group Aust N Z J Psychiatry 2002

21. Dunedin Birth Cohort Study Association between cannabis use in adolescence and schizophrenia and depressive symptoms and disorders at age 26 (n=759), controlling for childhood psychotic symptoms and use of other drugs in adolescence Cannabis at 15, OR = 4.50 (1.11 to 18.21) Cannabis at 18, OR = 1.65 (0.65 to 4.18)

22. Population Attributable Risk: Smoking, lung cancer and CHD Source: Epidemiology in Medicine Little Brown, Toronto, Hennekens & Buring (1987), p 94

23. GPRD Study questions • What is the relative risk of psychiatric illness among substance abusers compared to non substance abusers? • What is the relative risk of substance abuse among psychiatric cases compared to non psychiatric cases? • How has the proportion of comorbid patients with a primary substance abuse diagnosis changed from 1993 to 1998?

24. Time sequence between mono and dual diagnosis Entry into cohort (N= 1.8 million patients) No substance abuse or psychiatric illness in previous year 1 No diagnosis of substance abuse or psychiatric illness 2 Diagnosis of ONLY a) substance abuse or b) psychiatric illness 3 Diagnosis of substance abuse then psychiatric illness 4 Diagnosis of psychiatric illness then substance abuse

25. Study Cohorts

26. Ordering of first diagnoses among comorbid patients

27. Median interval from first diagnosis to comorbid diagnosis

28. Time ordering of comorbidity in relation to psychiatric diagnoses

29. Risk Exposure and Disease Outcome

30. Relative risk of psychiatric illness and substance abuse

31. POPULATION ATTRIBUTABLE RISKProportion of illness in the population attributable potentially explained by the exposure

32. Changes in baseline conditions

33. Summary (1) • The numbers of individuals newly developing comorbidity in primary care is increasing year-on-year. • Does the increase in comorbidity reported here represent an actual increase in the prevalence of comorbid conditions or the medicalisation of social, economic or personal problems?

34. Summary (2) • Does active early recognition of comorbidity lead to better outcomes? • The findings of the present study do not contradict studies in different populations which have found a link between certain forms of drug use and psychiatric illness. However they suggest that attempts to prevent comorbidity by focusing on substance abuse will meet with only very limited success.