Herbal medicine is not unpopular. You just have to look in the right places for it. I can tell you that a medical pharmacology database will not be your best source for information on natural medicine, nor will it contain the proper references or even tell you where you can find the proper references. It has nothing to do with its popularity or lack thereof - you are searching in the wrong places.
The majority of 'drugs' are synthetic because that's what our regulatory structure currently supports. Do not underestimate the effect of the profound influence that pharmaceutical companies and health insurance companies have had on both conventional medical education and the regulatory system that approves drugs.
Be careful not to use the same standard of review for herbal medicine that is used for billion-dollar synthetic drugs and their analogues. If you use the same standard, the same thinking and the same sources, then what other choice do you have but to think herbal medicine is unpopular or somehow invalid? Does your perspective really have the breadth it needs to make a judgment in this area?
Herbal medicine and conventional medicine are slowly being integrated more and more, but the process is slow because there are a lot of competing interests at stake. For example, under the current system, most natural cures/herbal medicines do not have the same profit potential that synthetic drugs have because you can't patent something that you didn't create! (This is the basic idea. Legal patents and other intellectual property protection mechanisms are the tools that enable massive profits in this industry. They're the same tools that underlie the regulatory system.)
You said you were a pre-pharma student. Maybe look into programs of naturopathy. If you are considering conventional medical school, then do a residency in naturopathic medicine. These programs are available in many countries, and there are even introductory seminars you can take in herbal medicine that will give you the foundation you need to understand the role of herbal medicine.
In the meantime, if I were you, I would just keep in mind that pharma education can only provide its own perspective. If you want more, you need to look elsewhere. For everything you learn and everything you think, just ask yourself - is that really the whole story? It will help you find better answers.
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James L Poole
I am a holistic health therapist: Emmett Technique practitioner, aromatherapist, nutritional therapist, and Reiki healer. This is my blog about natural healing. For more frequent updates, please check my Facebook group page.