To obtain more information about the treatment effects in different scenario's for the missing endpoint-assessments, the robustness of the results was analyzed. The purpose of this analysis was to investigate whether the - possibly - observed difference in effectiveness between the treatment conditions would hold if the missing endpoint-assessments would be dealt with using an even more conservative scenario than LOCF, which would reduce the contrast between the experimental and control condition. To this end, the robustness of the findings was investigated in a worst-case scenario, in which the patients with missing endpoint-assessments were considered as non-responders in the co-prescribed heroin condition, and as responders in the methadone alone condition.