I mean, Ozempic is still very much a diabetic drug, its just that its gained popularity, far and away, beyond diabetics for its weight loss properties in everyone.

Minoxidil started as a heart medication

Warfarin (Coumadin) is used as a blood thinner, but was created as rat poison

Dynamite TNT. In 1863 Julius Wilbrand synthesized trinitrotoluene (TNT) while experimenting with new yellow dyes for the textile industry.

I dunno that those are opposites.

Tbh, I don't think there's really any examples of the idea, not that would hold up as a science answer.

Not to say that there aren't plenty of medicines that ended up pretty far away from what the original research was towards, and there's a perfect example with minoxidil imo. But I can't call it an opposite in any but the most abstract way.

Mind you, if some of the hints about it being a viable component of treatment for ovarian cancer end up panning out, id have to shrug and smile if someone called that opposite lol.

But, yeah, finding unintended uses for drugs is super common, it's just that the underlying reason it ends up working isn't really an opposite, just unexpected. People have already given great answers for that side of things, and I can't improve on them tbh.

Wasn't ozempic also indicated for alcohol addiction? I know that amphetamine and related compounds are indicated for weight loss and attention deficit. Seems like whenever we create a psychoactive drug it is a blunt instrument that has multiple side effects.