The ethical doctrine of double effect permits health care professionals to administer potentially fatal medication, provided that their intentions are purely to control symptoms. In this article, the legal status and scope of the doctrine will be analysed, and it will be argued that the law in this context is unclear, incoherent and partial in its application. The problems are not exclusively legal in nature, however, because health professionals have been critical both of the doctrine itself and of the lawyers' understanding of the concept. It will be concluded that clarification and appropriate enforcement are needed if the doctrine and the law are to retain credibility.