In vogue right now are herbs that can used in lieu of drugs, but essentially for the same rationale. This is the case with saw palmetto which is prescribed for prostatic hypertrophy instead of the drug proscar or st. In the former case, the herb often works better and in the latter, at least as well. In both cases, the incidence of side effects are dramatically lessened as compared to the drugs. Why herbs may work better in some cases is a matter of speculation, so here's mine.
Herbs have multiple active ingredients, as well as vitamins, minerals and essential fatty acids.
In most cases, the amount of any particular biochemical is relatively small compared to the amount of a drug dosage. So the effects would be expected to be weaker than a drug. Well this is both correct and not. If one requires a highly specific effect dependent on a very large concentration of a single active ingredient, then drugs are the way to go. This would be the case for an acute asthmatic attack or a seizure, for instance.