Background: Initiation of drug use and progression to abuse/dependence involve complex pathways. Potential risk factors may correlate with initiation or progression or both. Are there risk factors that associate with illicit drug use or illicit drug abuse/dependence? Is the magnitude of the association the same for use and abuse/dependence? Does this pattern of association differ across categories of drugs? Methods: We used data from female-female adult twins to assess the association of 26 putative risk factors with use and abuse/dependence of six illicit psychoactive drugs. Drug involvement was represented by independent dichotomous outcomes and by a single ordinal variable. Odds ratios were obtained by logistic regression and a continuation ratio was used to test the magnitude of association. Results: Factors associate in similar patterns with different drug categories. Some associated factors interact only with initiation while others relate with both stages. There is a stronger association of significant socio-demographic factors with drug use while the psychiatric diagnoses are more strongly associated with progression to abuse/dependence. Conclusions: Risk factors may be use-specific, abuse/dependence-specific or common to use and abuse/dependence. The trend of associations is similar across different illicit drugs. This suggests complex, interacting pathways that determine drug habits in individuals. These results are hypothesis-generating and future studies of causal relationships may draw from the outcomes presented in these analyses. (Author' s abstract)