Physicians do not systematically prescribe placebos to their patients. Hence they have no way of comparing the effects of the drugs they prescribe to placebos. When they prescribe a treatment and it works, their natural tendency is to attribute the cure to the treatment. But there are thousands of treatments that have worked in clinical practice throughout history. Powdered stone worked. So did lizard's blood, and crocodile dung, and pig's teeth and dolphin's genitalia and frog's sperm. Patients have been given just about every ingestible - though often indigestible - substance imaginable. They have been 'purged, puked, poisoned, sweated, and shocked', and if these treatments did not kill them, they may have made them better.
Irving Kirsch, The Emperor's New Drugs: Exploding the Antidepressant Myth
antidepressants, history, treatments