The average doctor, educated in allopathic medicine, is very knowledgeable about illness and the use of pharmaceutical drugs for treatment, but often knows very little about herbs or their appropriate application for certain conditions. Naturally most have very little hesitation in offering a negative opinion about the use of herbs as they have simply not been part of their medical education and it is of course a responsible reaction from their perspective. This is unfortunate as they are also fully aware of the toxicity and side-effect that result from the use of many allopathic drugs, something that has almost become accepted as normal and unavoidable. In many cases drugs are administered to treat the side effects of other drugs.
In many cases the application of herbs is an appropriate alternative, or complement but it does need to be put forward with significant knowledge of the condition and the body as a whole at the time of that condition. Equally important is a deep knowledge and experience in the application, blending and administration of herbs. When this combination exists the results can be remarkable and without toxicity or side-effects.
Herbal product's are classified as GRAS (Generally Regarded As Safe) by the US FDA. That does not mean that they are approved by the US FDA or anyone else, what it means is that they generally don't have to be because they don't carry enough risk to warrant the expense or concern. You may ask your doctor if ANY of the medications he/she prescribe daily carries the GRAS classification? You might find the answer interesting.
The most damaging herb or natural product ever sold in the U.S. has not accounted, in its entire lifetime, for even a fraction of the deaths or injuries caused by long-term, negative side effects of any one of the most popular drugs in a single year. That's why herbs and other natural products are classified as they are, "generally regarded as safe".