[kale]

The FDA has tiers of regulation. Things like "supplements" are loosely regulated, while "pharmaceuticals" are much more highly regulated.

With supplements, the FDA pretty much lets things go until they start causing problems. DMAA was legal for a long time until people started having heart attacks. Melatonin, which is a straight-up hormone, is over-the-counter in the US, and it's by prescription only in Europe.

Now, if you're marketing something as a treatment for a disease, you have to have concrete data to back it up.

So it's very possible to have something that the FDA will let you sell as a supplement (i.e. there's no evidence that it's dangerous), but not make any claims about its efficacy (i.e. you can't say it will treat XYZ).

I experimented with nootropics at one point of my life (found them worthless, FYI), and it was funny how all of the labels just stated what it was, purity, and a blurb about the company selling it. There was no language whatsoever telling you what the supplement was for. Just a giant "PIRACETAM" label on the front.