The principle of double effect
- Principle
An act with one good and one bad effect may be permissible if only the good is intended and the bad is foreseen, not wanted.
What it is
The principle of double effect is used when one act has a good effect and a bad one. Its origin is usually traced to Thomas Aquinas, writing on self-defence. It separates what is intended from what is only foreseen. In medicine it applies above all to symptom relief at the end of life and to some conflicts between the life of the mother and that of the fetus. It has critics: intention is hard to verify, and the principle does not settle every case.
What it requires
- The act itself must be good or neutral (for example, relieving pain).
- The intention must be the good effect; the bad effect is foreseen but not sought.
- The good effect must not depend on the bad one (relief is not achieved by causing death).
- There must be a proportionate reason: an important good that justifies the risk.
In clinical practice
- Symptom control at the end of life: the dose is adjusted to the symptom, not to shorten life; properly adjusted, opioids rarely shorten it.
- Palliative sedation: the aim is to relieve a symptom that does not respond to other treatment, not to cause death.
- Cancer of the uterus in a pregnant woman: hysterectomy aims to save the mother's life; the death of the fetus is foreseen, not sought.
- Recording the symptom, the intention and the proportion in the medical record helps show the act was right.
Limits and exceptions
- Intention cannot be seen: it is inferred from the indication, the symptom-adjusted dosing and what is recorded.
- Some authors argue that terminal sedation intentionally hastens death and is not covered by double effect.
- It is a guide, not an algorithm: judging proportion is still required.
Test yourself
Think of the answer, then tap the question to see it.
What are the four conditions of the principle of double effect?
A good or neutral act; only the good effect intended; the good not achieved through the bad; and proportion between the good sought and the harm tolerated.
Why is pain relief with opioids at the end of life justified by double effect?
Because the aim is to relieve pain and the dose is adjusted to the symptom; any shortening of life is foreseen, but neither sought nor the means of relief.
What separates double effect from deliberately causing death?
Intention: in double effect the harm is foreseen and tolerated, not wanted, and the good is not obtained through it.
To which thinker is the origin of the principle of double effect attributed?
Thomas Aquinas, in his analysis of self-defence.
Connections
Educational content on ethics and health law; not legal advice. Laws and case law change: each page links the official text and says when it was last checked. For a real case, read the text in force and ask a lawyer or the medical ethics tribunal.
Sources: Doctrine of Double Effect (Stanford Encyclopedia of Philosophy, 2023).
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Representative model, for educational purposes only.