By Alison McIntyre
The Stanford Encyclopedia of Philosophy
The doctrine (or principle) of double effect is often invoked to explain the permissibility of an action that causes a serious harm, such as the death of a human being, as a side effect of promoting some good end. According to the principle of double effect, sometimes it is permissible to cause a harm as a side effect (or “double effect”) of bringing about a good result even though it would not be permissible to cause such a harm as a means to bringing about the same good end.
For example, a physician's justification for administering drugs to relieve a patient's pain while foreseeing the hastening of death as a side effect does not depend only on the fact that the physician does not intend to hasten death. After all, physicians are not permitted to relieve the pain of kidney stones or childbirth with potentially lethal doses of opiates simply because they foresee but do not intend the causing of death as a side effect! A variety of substantive medical and ethical judgments provide the justificatory context: the patient is terminally ill, there is an urgent need to relieve pain and suffering, death is imminent, and the patient or the patient's proxy consents. Note that this last constraint, the consent of the patient or the patient's proxy, is not naturally classified as a concern with proportionality, understood as the weighing of harms and benefits.
The entry entry is here.