Avoid supplements that make drug-like claims.
Supplements are not drugs, so companies cannot legally claim that their products can cure, treat, or prevent diseases or any health condition. What they can say, however, is that a supplement "supports heart health" or "helps with blood sugar management" or "builds strong bones" — just so long as the claim refers to supporting the normal functioning of the body.
The legitimate supplement brands understand the difference between legal and illegal health claims and don't break the law. But there are plenty of shady companies out there that do. And since the FDA doesn't evaluate supplements or their claims before products hit the market, law-bending manufacturers can usually get away with claims like "prevents cancer" or "reverses diabetes" for a while before they get caught. If a supplement makes a disease claim, that's a clear sign it's bunk.