Supplementing one's diet with medical herbs is an important contribution to a vegan diet. Medical herbs can be correctly taken even when one is well to prevent future illnesses such as when using Reishi Mushrooms or when using them for sports augmentation or to assist with pregnancy or menstruation. It is important when beginning to always go to a state licensed doctor of Herbl Medicine.
The field of Medical Herbalogy is divided into three fields, each is licensed by the state of California as well as other states for the practicing of medicine. The three classical fields of herbal medicine are Western Herbalogy which utilizes herbs from around the world available by growers who raise them with California and Oregon standard of organic farming, TCM or Traditional Chinese Medicine which imports its herbs from China and Taiwan but you must explain you only want vegan medicine, and Ayurvedic Medicine which relies on herbs from India where you also must explain you only want vegan medicine.
You can learn about herbal medicine for free on the web by listening to past and live shows of "The Herbal Highway" by Karen Sanders on KPFA in Berkeley. The past 20 or 30 years of shows are found on different web sites and players than KRFAs.
The best book on the topic is:
"The Desktop Guide to Herbal Medicine: The Ultimate Multidisciplinary Reference to the Amazing Realm of Healing Plants, in a Quick-study, One-stop Guide"
by Brigitte Mars