They tried to pass a bill regulating them in the early 90s. All the supplements companies took out ads screaming that doctors were trying to take your vitamins away. Very unpopular, bill went down in flames.

Like no, doctors just don't want people getting amphetamines in their creatine supplement. Or unexpectedly getting St John's wart in some supplement that doesn't list it as an ingredient, suddenly causing severe and dangerous interactions with multiple medications the person is taking. It says a lot about the supplement industry that they fight tooth and nail against any regulation that would require them to accurately report what's in the bottle. They can basically just make it up out of thin air as it is. Tons of supplement makers with expensive "proprietary blends" where they don't even attempt to show what's inside, then market them toward incurable diseases like alzheimers, very carefully avoiding the name of the disease in advertising, and taking money out of their pockets in exchange for false hope. Looking at you neuriva. If your blend actually works, test it, patent it, become billionaires (they won't because it doesn't).

And some being sold are just straight up harmful. You can hop on Amazon right now and buy 250 mg /pill vitamin b6 supplements. If they're reporting that accurately, that's a toxic dose that could be harmful to your health and even cause neuropathy (ironically many who take it are hoping it will help with neuropathy, but that's only true if you're deficient, and you don't need anywhere near that amount even if deficient).

where downsides

I the FDA can't even keep up with trying to approve legitimate pharmaceutical drugs, let's not task them with looking at random s*** too.