Drugs must undergo double-blind, randomized testing. Drugs must provide documentation about use, safety, ingredients, indications, warnings and dosage. Herbal supplements require no such regulation. In a paper he recently presented to the National Institute of Health's new Office of Alternative Medicine, herb honcho Rob McCaleb theorized that the demand for strict scientific regulation of herbal supplements was hindering access to traditional healing techniques. The inventors of Prozac probably wouldn't mind that kind of investment, given the juicy patent waiting at the end of the laboratory trail.
Nobody gets a payoff.
He who patents, prospers. Because no one can patent an herb, no one can exclusively profit from it. Nobody, except cancer patients and their families, that is. In a capital-driven society, what generates patented profits is what we get. It's not because they are angels from heaven.