Addiction (1993) 88, 257-263 RESEARCH REPORT The effects of methadone on immune function among injecting drug users: a review COLIN McLACHLAN', NICK CROFTS', ALEX WODAK' & SUZANNE CROWE' 'Department of Psychology, School of Behavioural Sciences, Latrobe University, Bundoora, Victoria, ^Epidemiology and International Health, The Macfarlane Bumet Centre for Medical Research, Faitfield, Victoria, ^Alcohol and Drug Service, St Vincent's Hospital, 366 Victoria St, Darlinghurst, NSW and The National Drug and Alcohol Research Centre, University of New South Wales & ''AIDS Pathogenesis Research Unit, The Macfarlane Bumet Centre for Medical Research, Fairfield, Victoria, Australia. Abstract Methadone maintenance therapy is advocated as a major preventive strategy for the spread of the human immunodeficiency virus (HIV) and other bbod-bome infectious agents among injecting drug users (IDUs) because of its effects in decreasing the frequency of injecting and presumably sharing of equipment. As an opioid agonist, methadone may share the direct and indirect immunoregulatory effects of other opioids, and thus affect susceptibility to, and the natural history of, HIV infection. Available evidence pertaining to methadone and immune function is reviewed. The long-term immunosuppression observed in heroin injectors on present (incomplete) evidence appears to be caused by factors associated with a drug-using lifestyle rather than by a direct action of heroin. Although data are conflicting, it is most likely that methadone does not significantly impair immune function and is safe for HIV-infected IDUs, possibly even allowing some improvement of immune function to occur. The increasing reliance placed on methadone maintenance to control the epidemic of HIV infection in IDUs requires that remaining uncertainties regarding methadone and immune function are clarified urgently. Introduction C (HCV) and D (HDV), due to the reuse of Injecting drug users (IDUs) are at increased risk contaminated injecting equipment.' of the transmission of blood-borne infectious Rates of HIV infection among IDUs vary agents such as the human immunodeficiency widely in different parts of the world. Seropreva- virus (HIV), human T-leukaemic viruses lences as high as 50% to 80% in groups of IDUs (HTLV-I/II) and the hepatitis viruses B (HBV), have been reported in New York City,^ Edin- burgh,'''' Rome,' Milan,' Bangkok' and Myanmar (Burma),^ with evidence of rapid viral Correspondence should be addressed to: Nick Crofts, Epi- spread at all these sites. IDUs as a risk group demiology and International Health, The Macfarlane Bumet • j l i i • l c Centre ffr Medical Research, P.O. Box 65, Fairfield, Victoria Constituted the second largest nsk category of 3078, Australia. newly diagnosed acquired immunodeficiency 257