Herbs Contain Many Different Chemicals

An important distinction between drugs and herbs is that most drugs consist of a single chemical compound, whereas herbs consist of many different ones. Of all the chemicals in herbs, some may be beneficial, some may be harmful, and a large number have unknown effects on the human body. Fortunately, most of the chemicals are not toxic, and most are present in small enough quantities that significant harmful effects are unlikely.

Many chemicals with beneficial activity against disease have been identified in herbs. It is estimated that 25 percent of prescription drugs and 60 percent of over-the-counter drugs are derived from plants. Well-known examples of these drugs are digitalis, which is derived from the foxglove plant, and quinine, which is derived from South American Peruvian bark. Steroids, which are used to treat multiple sclerosis (MS) attacks, have a very specific chemical structure. Chemicals with steroid-like structures and biologic effects have been identified in Asian ginseng (ginsenoside) and in licorice (glycyrrhizic acid).

Herbs may contain chemicals that have harmful effects. For example, the lily-of-the-valley plant contains potent heart toxins. Some herbs, such as chaparral and comfrey (or contaminants mixed in with the herbs), have been associated with a severe liver toxicity that has led to death or the need for liver transplantation. An example of a tragic case of liver injury was described in February 1999. A 28-year-old man with mild MS was treating his disease with zinc and two herbal medicines, scullcap and pau d'arco. He developed severe liver injury and died. The liver injury was believed to be due to a chemical contaminant in the scullcap.

Fortunately, most of the chemicals in herbs do not have toxic effects. For most herbs, the majority of the chemicals probably have neither beneficial nor harmful properties; if demonstrated beneficial effects of an herb exist, they probably are due to one or several of the many chemicals present. Thus, for many herbs, it is likely that one or a few chemicals could be producing a beneficial effect and that the remaining chemicals do not have any beneficial or harmful effects.

It is sometimes claimed that herbs cannot have harmful effects because the chemicals in them are present in such small quantities. It is also claimed that herbs have beneficial qualities. These two statements are not consistent with each other. If a therapy is strong enough to produce beneficial effects, it usually is also strong enough to produce harmful effects. As more research is conducted, it may indeed be found that, relative to prescription medications, herbs generally have fewer side effects, but are also somewhat less effective.

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