The uses of plants for medicine and other purposes changed little in early medieval Europe. Many Greek and Roman writings on medicine, as on other subjects, were preserved by hand copying of manuscripts in monasteries. The monasteries thus tended to become local centers of medical knowledge, and their herb gardens provided the raw materials for simple treatment of common disorders. At the same time, folk medicine in the home and village continues uninterrupted, supporting numerous wandering and settled herbalists.
Most herbalists concede that pharmaceuticals are more effective in emergency situations where time is of the essence. An example would be where a patient had elevated blood pressure that posed imminent danger. However they claim that over the long term herbs can help the patient resist disease and in addition provide nutritional and immunological support that pharmaceuticals lack. They view their goal as prevention as well as cure.
Herbalists tend to use extracts from parts of plants, such as the roots or leaves but not isolate particular phytochemicals. Pharmaceutical medicine prefers single ingredients on the grounds that dosage can be more easily quantified. Herbalists reject the notion of a single active ingredient. They argue that the different phytochemicals present in many herbs will interact to enhance the therapeutic effects of the herb and dilute toxicity.