As the Drug Policy Alliance recently noted, the Food and Drug Administration is cracking down on psychoactive herbs "marketed as street drug alternatives." Many of these products contain ma huang or other sources of ephedrine, which are perfectly legal (so far) to sell over the counter as dietary supplements. But when the manufacturer intimates (or baldly states) that taking them might be enjoyable, the FDA says, they "are not dietary supplements under the legal definition, because they are not intended to be used to augment the diet, to promote health or to reduce the risk of disease." The same reasoning applies to psychedelic herbs, such as ayahuasca and salvia divinorum, that the government has not quite gotten around to explicitly banning. The FDA maintains that herbal preparations sold "to affect the mental or psychological states of those taking the products" have to be approved by the government as "new drugs"–even if they've been used for thousands of years.
That's a path no company is likely to take, since it would mean investing many millions of dollars in a drug that could not be patented. But it would be interesting to see how the FDA would evaluate the efficacy of drugs whose sellers promise "hours of bliss," "incredible visionary & mystical experiences," or "an overall stimulation of the mind, body and spirit."