Warfarin is the primary ingredient in rat poison, but we do controlled microdoses with frequent monitoring, and that has been the gold standard for blood clot prevention for decades. Factor Xi drugs are now the gold standard but only due to slightly less bleeding risk than warfarin. Last I checked the clot prevention is still considered equal to warfarin, but those new drugs are expensive as hell at over $500/month if your insurance doesn’t cover it.

Besides, some of us get migraines so painful and enduring that in the moment, that being prescribed a bullet starts to sound reasonable. Botox is safely used for wrinkles and overactive sweat glands - things that people can easily live without. So why not use it in situations where it can alleviate chronic pain and suffering with minimal (or even desired) side effects if done right? Other than the localized effects, it can have a lot fewer systemic effects than some of the drugs used.