The science of medicine

[Rihanna]

Doctors have been treating people for many thousands of years. The earliest written description of medical treatment is from ancient Egypt and is over 3,500 years old. Even before that, healers and shamans were likely providing herbal and other remedies to the ill and injured. A few remedies, such as those used for some simple fractures and minor injuries, were effective. However, until very recently, many medical treatments did not work and some were actually harmful.
Two hundred years ago, common remedies for a wide range of disorders included cutting open a vein to remove a pint or more of blood and giving various toxic substances to produce vomiting or diarrhea—all dangerous to a sick or injured person. About 120 years ago, along with mention of some useful drugs such as aspirin and digitalis, The Merck Manual mentioned cocaine as a treatment for alcoholism, arsenic and tobacco smoke as treatments for asthma, and sulfuric acid nasal spray as a treatment for colds. Doctors thought they were helping people. Of course, it is not fair to expect doctors in the past to have known what we know now, but why had doctors ever thought that tobacco smoke might benefit someone with asthma?
There were many reasons why doctors recommended ineffective (and sometimes harmful) treatments and why people accepted them:

Typically, there were no effective alternative treatments.
Doctors and sick people often prefer doing something to doing nothing.
People are comforted by turning problems over to an authority figure.
Doctors often provide much-needed support and reassurance.

Most importantly, however, doctors could not tell which treatments worked.