I'd say that, at worst, they can be bad for you. You can overdose some of them. And if you're talking about herbal supplements, it's probably even worse than th

I'd say that, at worst, they can be bad for you. You can overdose some of them. And if you're talking about herbal supplements, it's probably even worse than that, i.e. some of them can actively be bad for you (e.g. St. John's wort if you're taking other medications). And then, there's the problem of quality. Some supplements contain substances they shouldn't contain (e.g. heavy metals or others). I'm a fan/user of supplements/nootropics, but they shouldn't be taken lightly.