Drug use disorders in the polydrug context: new epidemiological evidence from a foodborne outbreak approach.

As epidemiologists studying foodborne illness outbreaks, we do not ask luncheon attendees to say which food caused their illnesses. Instead, we use measurement and analysis methods to estimate food-specific risk variations. Here, we adapt the foodborne outbreak approach to develop new estimates of drug use disorder risk for single-drug and polydrug users, without attributing the syndrome to a specific drug when multiple drugs have been used. We estimate drug use disorder risk for cannabis-only users as a reference value. We then derive comparative relative risk estimates for users of other drug subtypes, including polydrug combinations. Data are from the 2002 to 2003 U.S. National Comorbidity Survey Replication, a nationally representative sample of household residents (18+ years), with standardized drug use and drug dependence assessments. Multiple logistic regression provides odds ratio estimates of relative risk. With this approach, for every 1000 cannabis-only users, an estimated 17 had become cases (1.7%). By comparison, polydrug users and cocaine-only users had much greater cumulative incidence (>10%), even with adjustment for covariates and local area matching (P < 0.001). Using this approach, we find exceptionally low risk for cannabis-only users and greater risk for polydrug and cocaine-only users.