Thorazine, or chlorpromazine, was the first antipsychotic. It freed many people with severe schizophrenia from mental asylums, but that's not why it was developed. It was first tested because it's an antihistamine. Yes, like the allergy medications.
The incessantly itchy eyes and noses that some people get in the spring is the result of their body desperately trying to keep them alive. It senses an invader, and kicks into gear to fight this invader off. The fact that the invader happens to be harmless pollen cuts no ice with the body, so often the best way to tamp down the reactions is to tamp down the bodily system.
Antihistamines are good at that. They decrease the body's response to a lot of different signals. Sometimes this causes allergy sufferers more agita, as the antihistamines suppress body systems that are responsible for things such as salivation and alertness.
In 1949, a Henri Lavorit, a French doctor working in Tunisia, saw huge potential in antihistamine's suppression of bodily systems — including the autonomic nervous system responsible for many unconscious body responses. Too many patients were dying during surgery, due to the body's natural responses to being cut open, manipulated, and stitched back up. If Lavorit could suppress that response, he could save many lives.
One particular antihistamine, known as chlorpromazine, seemed to do a good job lowering blood pressure, but it also rendered patients utterly indifferent to their upcoming surgery. Lavorit wanted to use it on nervous surgical patients, but he was stymied when it did too good a job lowering blood pressure. The patients fainted.
Looking for a useful application for this drug, he tried psychiatrists treating schizophrenic patients. Up until then, the psychiatrists had been doing nothing more than knocking their patients out with sedatives, which were the only known way to treat mania and schizophrenia. When a schizophrenic patient took chlorpromazine, he was calm and rational in three weeks. In another few weeks, he went home. This was something that no one had ever seen before.
Today, the most popular theory is that chlorpromazine, better known as Thorazine, treats schizophrenia by doing just what antihistamines are meant to do — blocking an overactive bodily response. Too much dopamine can cause visual and auditory hallucinations. Thorazine blocks dopamine receptors. Some doctors disagree, and the "dopamine theory" of schizophrenia isn't universal, but few disagree with the notion that chlorpromazine was a revolution in psychiatric treatment at the time.
Top Image: Epsos.de