Plants contain phytochemicals that have effects on the body. Throughout history, from the Bible, Koran, Siddhar poems of Tamils,Vedas and other old texts, the medicinal benefits of herbs are quoted.

There may be some effects when consumed in the small levels that typify culinary "spicing", and some herbs are toxic in larger quantities. For instance, some types of herbal extract, such as the extract of St. John's-wort (Hypericum perforatum) or of kava (Piper methysticum) can be used for medical purposes to relieve depression and stress. However, large amounts of these herbs may lead to toxic overload that may involve complications, some of a serious nature, and should be used with caution. One herb-like substance, called Shilajit, may actually help lower blood glucose levels which is especially important for those suffering from diabetes. Herbs have long been used as the basis of traditional Chinese herbal medicine, with usage dating as far back as the first century CE[4] and far before.

Medicinal use of herbs in Western cultures has its roots in the Hippocratic (Greek) elemental healing system, based on a 4-fold elements healing metaphor. Famous herbalist of the Western tradition include Avicenna (Persian), Galen (Roman), Paracelsus (German Swiss), Culpepper (English) and the botanically inclined Eclectic physicians of 19th century/early 20th century America (John Milton Scudder, Harvey Wickes Felter, John Uri Lloyd). Modern pharmaceuticals had their origins in crude herbal medicines, and to this day, many drugs are still extracted as fractionate/isolate compounds from raw herbs and then purified to meet pharmaceutical standards.