In the study, heroin was prescribed in an intravenous injectable and inhalable form. For the study on injectable and inhalable heroin, two separate protocols were developed. These protocols are identical, with the exception of those aspects which refer to the route of administration of the co-prescribed heroin (e.g. inclusion criteria). The rationale for conducting two separate trials, each requiring a separate randomization procedure and a separate control group, was that inhaling and injecting heroin addicts were expected to differ considerably in terms of - for example - ethnicity, pattern of drug use, and health status. Given these expected differences, it could not be assumed a priori that these two populations would respond similarly to the experimental treatment. In addition, it could not even be excluded a priori, that one group would respond favorably and the other group would not respond or even respond unfavorably to the experimental treatment. Lastly, route of administration is an important parameter in any clinical trial involving an investigational product.

The decision whether the patient should receive the co-prescribed heroin in inhalable or injectable form was made by the treating physician in agreement with the patient, on the basis of the patient's physical health condition and his past and current pattern of heroin administration. Patients who had been assigned to the injectable route of heroin administration in the trial had the opportunity to switch to medically prescribed inhalable heroin. Both forms of heroin, however, were not prescribed simultaneously to the same patient. If an injecting patient had switched to prescribed inhalable heroin, he was required to stay in the inhalable condition for a minimum period of two weeks before he was allowed to switch back to injectable heroin on medical prescription. Participants who had been assigned to the inhalable condition at the start of the study were not allowed to switch to medically prescribed injectable heroin in the study. Lastly, it is important to note that the patients remained in the trial they were assigned to at the start of the trial, regardless possible switches in their route of administration of the medically prescribed heroin during the trial. Hence, patients in the injectable trial who had switched to prescribed inhalable heroin during the trial, were analyzed as participants in the injectable heroin trial.