Even before the development of man as a species, herbs have been used to treat disease. Animals often chew certain plants to induce vomiting or treat other conditions. Shamans, or tribal healers, most likely observed this behavior and developed a base of knowledge about what herbs and plants were most effective and passed that knowledge down through the generations. In addition to treating disease and injury, the body of knowledge included ways to use herbs to improve nutrition and improve mental health.

Despite its ancient history, herbalism has only recently reemerged as an accepted practice in the modern western world. In most European countries, once medical schools began training doctors in large numbers, the practice of herbalism fell into disfavor. In fact, many of the witch trials of the Middle Ages involved women who were actually herbalists. However, herbalism continued to be practiced uninterrupted in almost all non-industrialized countries and is still the favored method of treating disease in many parts of the world.

Studies in the United States on the efficacy of herbal remedies have been sparse, but in 2004 the National Center for Complementary and Alternative Medicine began funding larger studies. In Europe, more studies have been done and herbal remedies are more widely accepted. For example, St. John's Wort is an herb that can be used to control mood and was a widely accepted remedy for depression in Europe long before it gained favor in the United States.

Although many of our most popular medicines have been developed from plants, including quinine, digitalis and codeine, scientists have only recently begun to return to plants as sources to create new medications. However, the use of plants to create medications should not be confused with true herbalism which uses the plants themselves as medication.

Herbal medication can be delivered as a tea, where herbs are steeped in hot water. Herbs are also used in poultices, and to infuse steam or smoke which is breathed by the patient. Breathing the smoke from burning sage, for example, has been used as a treatment for asthma. Camphor is a plant whose smell is familiar to anyone who has used Vick's Vapor Rub. Breathing the scent of camphor helps clear the sinuses.

Because plants contain such powerful chemicals, there is some risk associated with herbal medicine. Dosage, for example, is hard to standardize and control since two plants of the same species might have completely different levels of the chemical compounds necessary for healing. Also, herbal remedies can interact with more traditional drugs that a patient might be taking.