Heroin prescription involves the medical provision of heroin in the treatment of heroin addiction. Rudimentary clinical trials on that treatment modality have been carried out and others are currently underway or in development. However, it is questionable whether subjects considered for such trials are mentally competent to consent to them. The problem has not been sufficiently appreciated in ethical and clinical discussions of the topic. The challenges involved throw new light on the role of value and accountability in contemporary discussions (...) of mental competence. (shrink)