For one, herbal products are largely unregulated. The Food and Drug Administration considers herbs to be dietary supplements rather than drugs. This means that the manufacturer only has to prove that the herb is safe for human consumption and has no obligation to determine whether the herb really works for what they claim. Second, there is a risk of adulteration in some herbal remedies. If the value of the herb is high, some disreputable firms will undercut the product with a cheaper herb so that the consumer doesn't get the full-strength herb.
Chinese ginseng is an example of an herb for which adulteration has been a problem.
Lastly, when the consumer goes to purchase the desired herb, reading and understanding the labelling on the package can be mind-boggling. There are no well-defined doses for herbal medicines and to complicate matters further, there is no standard method for reporting the dosages on the packages. Besides needing a calculator to shop for herbs, a degree in pharmacy might be even more helpful. The only problem with that is that most pharmacists aren't trained in herbal remedies either. Now don't get me wrong.