I just took a class on 'drug plants' and it was extremely interesting and informative.
Most of the information can be found on the internet, but you need to be pretty careful. Keep in mind that most herbal medicines sold in stores are not FDA approved, and are not standardized, though there are attempts to making them safer. Studies conducted have shown that the dosage of certain "active compounds" can vary from bottle to bottle. Also, be aware of any contraindications with any other medications you may be on. Herbs do contain medically active compounds that can interfere with other medicines you are taking. I would even suggest searching for scientific studies/peer-reviewed articles done with certain herbs you are wanting to use to see what they were able to conclude or find.
Good luck on your research.