The study was conducted in two stages. Following an intensive political debate in September 1997, the parliament of the Netherlands approved the execution of a test period of three months in two cities (Amsterdam and Rotterdam), involving a total of 185 patients, of whom 50 patients would receive medically prescribed inhalable (n=25) or injectable (n=25) heroin (see also paragraph 1.1). The main purpose of the test period, which was conducted as an integral part of the total study, was to investigate whether the prescription of heroin was medically safe and would not lead to unacceptable public order problems. For the evaluation of these aspects, two independent committees - the National Safety Committee (LVC), and the National Committee on Public Order and Controllability (LCB) - were installed by the Minister of Health, Welfare and Sports, and the CCBH. Following the installation of the LVC and LCB in June 1998, the first treatment sites opened in Amsterdam and Rotterdam in July and August 1998. Four months later, in November 1998, the LVC and LCB reported to the Minister of Health, Welfare and Sports and to the CCBH that no unacceptable negative side-effects from the study or the treatment with co-prescribed heroin had been observed in either of the areas of interest. In accordance with the decision of the Dutch government and parliament in February 1999, the experimental treatment with co-prescribed heroin was subsequently continued in the already existing treatment sites in Amsterdam and Rotterdam, and extended in the course of the year 2000 to a total of the eight treatment units, situated in the six cities described earlier.