Abstract In an effort to inquiry 'self-medication hypothesis' in chronic psychosis and bipolar disorder heroin dependent patients a naturalistic comparative cohort study was designed with the aim of comparing, according to the presence of dual diagnosis, the clinical characteristics of heroin-dependent patients presenting for their first AOT. The main finding was that addictive (heroin) illness was more severe in bipolar 1 patients and less severe in chronic psychotic patients when compared with heroin-dependent patients without dual diagnosis. In the case of chronic psychotic patients, these differences do not allow us to exclude a therapeutic heroin use, at least at the beginning of their toxicomanic career, with limited progression of their addictive disease. This occurrence seems to be excluded for bipolar 1 heroin-dependent patients, who come to their first AOT with a more severe addictive disease.