Manufacturers do not have to prove or submit evidence of safety or efficacy. The FDA can take action but only after some sort of damage has been done. This is the same pathetic regulation now applied to cosmetics. In practice that means they really have to be dropping in the streets like flies or nothing is likely to happen. This also means you have to protect yourself when using herbal remedies as there is no regulatory force out there to do so.
Herbal medicines can make claims about effects on structure or function of the body.
They can not make claims about disease treatment or prevention. If an herbal medicine wants to make such claims, they have to be regulated as a drug. That's an example used by Beatrice Trum Hunter, a leading authority on nutritional products. But it doesn't seem to make much sense in practice. So the limitation about claims doesn't mean much in the marketplace and the legal restraint is easily evaded by cute semantic maneuvers.