Aversion therapy is a now largely discredited form of psychiatric treatment in which the patient is exposed to a stimulus whilst simultaneously being hurt or made ill.

The theory is that the patient will come to associate the stimulus with unpleasant sensations and will no longer seek it out.

In the past, gay men have been sentenced to compulsory aversion therapy by law. Treatment might consist of exposing the patient to pictures of nude men, whilst injecting apomorphine to produce violent illness. At least one person has died under this "treatment".

Milder and more benign forms of aversion therapy include putting unpleasant-tasting chemicals on the nails to discourage nail-chewing and giving alcoholics drugs that make the intake of alcohol unpleasant.

It is now generally recognized that it is unethical to use aversion therapies without the informed consent of the patient.