https://www.mcgill.ca/oss/article/medical-history/battling-baldness

It may seem hard to believe, but as late as 1942, male patients in some mental hospitals were castrated to quiet them. This extreme treatment did have some scientific basis, since testosterone, the male sex hormone produced by the testes, has been linked with aggression. One of the positive offshoots of this barbaric treatment was the knowledge gained about the effects of testosterone on the body Winfield State Hospital, a mental hospital in Kansas, became an ideal place for Yale anatomist James Hamilton to conduct a study of castrated men. One day, one of the patients who had been stripped of his manhood received a visitor, his identical twin brother. Dr. Hamilton was struck by the fact that the man was completely bald, while the inmate had a full head of hair. Could testosterone have something to do with baldness, the researcher wondered? To investigate this possibility Hamilton got permission to inject the castrated man with testosterone. Within six months the mental patient became as bald as his brother who had been progressively going bald over a twenty-year period. The baldness unfortunately was irreversible, but Dr. Hamilton had demonstrated clearly that testosterone levels could be linked to hair growth.

(http://www.autoadmit.com/thread.php?thread_id=5316244&forum_id=2#46122327)