In Ozone therapy the gas ozone (O₃) is used at carefully controlled levels. Some practitioners and advocates of alternative medicine claim it can be used for healing. These claims extend to a wide range of therapy. Ozone can be introduced to the body in many ways, including injection, transdermal application, insufflation (leaking the gas into the body), and breathing (bubbled through oil).

In the USA ozone therapy is illegal, as the FDA has not approved its use on humans. It is considered to be quackery by the mainstream medical and science communities. At least one death has been attributed to application of ozone through insufflation in the USA.

Becasue of its properties as a powerful oxidising agent, ozone has been found to convert cholesterol in the blood stream to plaque (which causes hardening and narrowing of arteries). Ozone has been studied extensively, and found to be carcinogenic to some animals (and not others), and a mutagen to some bacteria.