Homosexual aversion therapy notaby began in the early 1940s. Homosexuality, bisexuality, and transsexuality were viewed as sexual deviances caused by psychological maladaption. Queer patients were often taken to mental asylums involuntarily by family to be "cured", and aversion therapy was one of the many methods scientists attempted to do this. It was believed that conditioning patients to associate the sex they found attractive with unpleasant stimulus would cause them to lose their attraction and turn heterosexual. Doctors would take patients to viewing rooms and project images of people each patient would be attracted to. If they showed any signs of attraction or interest in the picture, the doctors would administer the unpleasant stimulus. The most notable of these stimuli was electroshock waves. Injecting drugs into the patient to cause nausea and vomiting was also common. Eventually, patients would associate these images with the shocks or drugs, and would be averse to looking at the screen. Continued exposure showed that, after time, this dislike would also be applied to real time, and patients would get upset looking at any member of their once-preferred sex.  

The cruelty of aversion therapy and other conversion methods eventually became a talking point in the psychological field. Human rights activits began to work for protections of queer people and make involuntary conversion illegal. As the century progressed, aversion therapy waned in popularity. In 1973, the American Psychiatric Associaton removed homosexuality from its list of diagnosable mental disorders. Treatment for the "condition" was no longer sanctioned. While this did not end the practice of aversion therapy, it did limit it, and the controversy around the practice made it extremely unpopular as more time passed. Today, queer aversion therapy is illegal in many states or countries. It is still used in some states, and has been expanded to try and deter sexual offenders like pedophiles.

Sources:

Blakemore, Erin. "Gay Conversion Therapy's Disturbing 19th Century Origins." History.com, 2019, www.history.com/news/gay-conversion-therapy-origins-19th-century. Accessed 7 October 2020.

Chenier, Elise. “Aversion Therapy.” GLBTQ Archive, 2015, www.glbtqarchive.com/ssh/aversion_therapy_S.pdf. Accessed 7 October 2020.

Editors of Encylopedia Britannica. Aversion Therapy. 23 Nov. 2018, www.britannica.com/science/aversion-therapy. Accessed 9 October 2020.