Most drugs are synthetic constructions of plants. The cost for FDA approval of any medicinal substance, natural or chemical, is millions of dollars. The down side of synthesizing plants to form drugs is in the loss of the synergistic relationship the “active ingredient” had with the entire plant. Those active ingredients alone can cause side effects that would have been balanced by the other parts of the plant.
The brilliance of herbs is in the specificity. A well-trained herbalist can combine individual herbs together to suit particular health needs in a safe and effective way.