APA Dictionary of Psychology

in ethics, the justification for an act undertaken with good intentions but with a foreseeable harmful side effect, even though it would not be ethical to bring about the harmful effect intentionally. For example, an end of life decision to provide a terminally ill patient with morphine for pain management and sedation has the potential to hasten the patient’s death. Also called doctrine of double effect (DDE); rule of double effect. [from Summa Theologica (II–II, Qu. 64, Art. 7) by Thomas Aquinas]