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What is the principle of double effect, and when does it apply in medicine?

Omar Farouk Contributor
· 4 replies
BioethicsMedieval ChristianScholasticism#double-effect#medical-ethics
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In palliative care we often say that giving high doses of morphine is permitted even if it might shorten life, because of the "principle of double effect". But I've realised I don't know exactly what the principle says or where it comes from.

What are the conditions? And is it a sound principle, or a convenient rationalisation?

4 answers

Accepted answer

  1. Aoife Brennan

    ✓ Accepted answer Contributor

    The principle is usually traced to Aquinas's discussion of killing in self-defence (Summa Theologiae II-II, q.64, a.7): one act can have two effects, one intended and one beyond intention.

    The standard modern formulation has four conditions:

    • the act itself must be good or at least morally neutral
    • the agent must intend only the good effect; the bad effect may be foreseen but not intended
    • the bad effect must not be the means to the good effect
    • there must be a proportionately serious reason for allowing the bad effect

    Applied to your case: giving morphine to relieve pain is a good act. The doctor intends pain relief, not death. Death is not the means by which the pain is relieved. And severe pain in a dying patient is a serious reason.

    Critics say the intended/foreseen distinction is psychologically unreal: if you know it will happen, you're responsible. Defenders reply that intention shapes what kind of act it is.

    1. Omar Farouk

      Contributor

      That's very clear, thank you, Aoife. I hadn't realised the third condition does so much work: death must not be the means. That's what distinguishes it from euthanasia.

      Helpful · 3

Other answers

  1. Elin Lindqvist

    Contributor

    A practical note: the evidence suggests that properly titrated opioids in palliative care rarely shorten life at all. So in everyday practice we lean on double effect less than people think. It matters more for palliative sedation.

    Helpful · 1
  2. Deepa Nair

    Contributor

    Courts have used something like it. In the English case of Dr John Bodkin Adams (1957), the judge directed that a doctor may give treatment to relieve pain even if it incidentally shortens life. The idea was already in the law well before modern bioethics.

    Helpful · 2

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