Under the FDA, drugs must pass clinical trials before being released to the public, and the tests need to prove each drug is safe, performing just as the manufacturer claims. After these trials, your doctor can prescribe the pharmaceutical to you.
But nutraceuticals are not subject to the same testing and regulations as pharmaceuticals. The aim of nutraceutical regulation is largely to ensure products are safe and properly labeled (much like supplements). It’s important to note that nutraceuticals do not face the same level of scrutiny as pharmaceuticals in regards to product claims and intended use. There is a perception, that may or may not be warranted, that this lack of oversight leads to products of variable quality and merit.