Many weight loss drugs were discovered haphazardly or by repurposing psychiatric drugs.

“if you look at the history of obesity drugs weight loss drugs i should say most of them were discovered in entirely haphazard ways like dinitrophenol was a high explosive that was used in world war one and somebody figured out if you take it it makes you lose weight and it does so by increasing your energy expenditures so some people manage to cook themselves and like literally from the inside out and then you look at other drugs and most of them are psychiatric drugs they're just repurposed psychiatric drugs that just happen to cause weight loss”