The placebo effect is mainly subjective. Placebos don’t work on patients who are asleep or unconscious. You have to know you’re being treated. Placebos don’t keep women from getting pregnant. They don’t cure cancer, heal broken bones, or do anything you can measure objectively. They work for more elusive complaints like headache, depression, itching, shortness of breath, tension, indigestion, and other symptoms that require us to accept the patient’s self-report of what he is experiencing.