COOCCURRENCE OF ABUSE OF DIFFERENT DRUGS IN MEN - THE ROLE OF DRUG-SPECIFIC AND SHARED VULNERABILITIES

Background: Previous research has demonstrated genetic and environment al influences on abuse of individual substances, but there is less kno wn about how these factors may influence the co-occurrence of abuse of different illicit drugs. Methods: We studied 3372 male twin pairs fro m the Vietnam Era Twin Registry. They were interviewed using the Diagn ostic Interview Schedule, Version III, Revised to investigate the exte nt to which the abuse of different categories of drugs occurs together within an individual, as well as the possibility that genetic and env ironmental factors are responsible for observed cooccurrence. Go-occur rence was quantified using odds ratios and conditional probabilities. Multivariate biometrical modeling analyses were used to assess genetic and environmental influences on co-occurrence. Results: Abusing any c ategory of drug was associated with a marked increase in the probabili ty of abusing every other category of drugs. We found evidence for a s hared or common vulnerability factor that underlies the abuse of marij uana, sedatives, stimulants, heroin or opiates, and psychedelics. This shared vulnerability is influenced by genetic, family environmental, and nonfamily environmental factors, but not every drug is influenced to the same extent by the shared vulnerability factor. Marijuana, more than other drugs, was influenced by family environmental factors. Eac h category of drug, except psychedelics, had genetic influences unique to itself(ie, not shared with other drug categories). Heroin had larg er genetic influences unique to itself than did any other drug. Conclu sion: There are genetically and environmentally determined characteris tics that comprise a shared or common vulnerability to abuse a range o f illicit drugs.