The Principle of Double Effect

The principle of double effect is a philosophical idea often invoked in discussions about palliative care. First proposed by St. Thomas Aquinas, it asks about the morality of an action that has both good and evil effects. For example, in a terminally ill patient, administering pain medications may end up shortening the patient's life, but if it is done with the intent of alleviating suffering rather than shortening life, then is it permissible? Thomas Aquinas argued that an action with both a good effect and a harmful one is justifiable if the nature of the act is morally good (or at least neutral), the agent intends the good effect, and the good effect sufficiently outweighs the negative effect.

At first, these criteria seem overly onerous but they adopt many key ethical ideas. For example, intent is central to an ethical framework endorsing the principle of double effect. Euthanasia is not permissible because a lethal dose of drug is given with the intent of killing a patient. But palliative sedation may be allowed because a dose of drug is given to alleviate a patient's pain and suffering even if there is a foreseeable consequence of the patient dying. In the same way, it is not permissible to bomb a civilian city in a legitimate war. But the principle of double effect may exonerate bombing a military target even if the agent knows that there are civilians there who will be killed. The intent of each scenario is different even if the consequences involve something negative.

Some people may find this argument distasteful. True utilitarians (or consequentialists) believe that an action's moral nature depends only on the net good or evil generated by the act. And others may find the distinction between intent and foresight blurred. If an action has a foreseeable inevitable harm, then can you intend the action without intending that inevitable harm?

In medicine, we do things that take the principle of double effect for granted. In many cases, the harmful effects are labeled side effects or complications. For example, we give patients medicines with the intent of helping the patient despite a foreseeable possibility of headache, nausea, vomiting, or even worse side effects. We justify this harm in a risk-benefit analysis. In taking out someone's infected appendix, we justify this action because it saves the patient's life despite an inevitable foreseeable consequence of pain. Appendectomies are intended to save lives not inflict pain. Those examples are not really that controversial. But what about this: let's say a pregnant patient has uterine cancer. Her physician thinks abortion is unethical and refuses to do abortions. However, the physician justifies taking out this patient's uterus - and thus, terminating the pregnancy - because of the principle of double effect, that she intends to save the patient even though she foresees the loss of the fetus, and that the risk-benefit analysis favors this action.

Note, the principle of double effect is not simply about risk-benefit analysis. Imagine in the last example that the patient was a 16 year old (I'm not sure why she might have uterine cancer, but we'll ignore that) and imagine the physician felt strongly that 16 year olds should not have children. Perhaps she does the hysterectomy with the intent of both curing the mother and aborting the fetus. Because she now intends this harmful consequence, she cannot justify her action by the principle of double effect.