Herbal products have gained increasing popularity in the last decade, and are now used by approximately 20% of the population. Herbal products are complex mixtures of organic chemicals that may come from any raw or processed part of a plant, including leaves, stems, flowers, roots, and seeds. Under the current law, herbs are defined as dietary supplements, and manufacturers can therefore produce, sell, and market herbs without first demonstrating safety and efficacy, as is required for pharmaceutical drugs. Although herbs are often perceived as “natural” and therefore safe, many different side effects have been reported owing to active ingredients, contaminants, or interactions with drugs.
Unfortunately, there is limited scientific evidence to establish the safety and efficacy of most herbal products. Of the top 10 herbs, 5 (ginkgo, garlic, St. John’s wort, soy, and kava) have scientific evidence suggesting efficacy, but concerns over safety and a consideration of other medical therapies may temper the decision to use these products.
Herbal products are not likely to become an important alternative to standard medical therapies unless there are changes to the regulation, standardization, and funding for research of these products.
Nearly 1 in 5 adults in the United States report taking an herbal product.1 Written records of the use of herbal medicine date back more than 5,000years.2 In fact, for most of history, herbal medicine was the only medicine. Even as recently as 1890, 59% of the listings in the US Pharmacopeia were from herbal products,3 and it has been estimated that as many as one third to one half of currently used drugs were originally derived from plants.4
Although many herbs are primarily of historical interest, thousands of herbal products are available over the counter and commonly used by patients in the United States. Therefore, an understanding of the composition, regulation, safety, and efficacy of herbs may assist clinicians in advising patients about the use of these products.
What’s in an Herb?
An herb can be any form of a plant or plant product, including leaves, stems, flowers, roots, and seeds. These plants can either be sold raw or as extracts, where the plant is macerated with water, alcohol, or other solvents to extract some of the chemicals. The resulting products contain dozens of chemicals, including fatty acids, sterols, alkaloids, flavonoids, glycosides, saponins, and others.5 Because any given herb contains multiple ingredients, some manufacturers attempt to create standardized herbal products by identifying a suspected active ingredient and altering the manufacturing process to obtain a consistent amount of this chemical.
For example, Figure Figure11 shows 1 high-pressure liquid chromatogram (HPLC) of the herb, Ginkgo biloba.6 This graph allows for the quantification of 5 of the flavonol constituents of ginkgo (rutin, quercitrin, quercetin, kaempferol, and isorhamnetin), and the manufacturer might standardize the extract to a specific level of 1 of these flavonoids. While this type of analysis is a potentially useful method of quantifying the chemical constituents of a given herb, variations in the analytical methods of herbs create uncertainty. For most herbs, the exact chemical, or combination of chemicals, that produce a biological effect is unknown, and it is therefore difficult (if not impossible) to create a precise “chemical fingerprint” of the optimum herbal product. Ginkgo, for example, contains at least 33 different chemical constituents, of which only 5 are shown in Figure Figure11.6 Similarly, it is not known whether the combination of chemicals in a given plant would produce a superior effect to 1 isolated chemical component of the herb. Finally, the process of performing an HPLC analysis is complicated, and different analytical techniques can lead to different estimations of the constituents of herbs. For Ginkgo, at least 7 different analytical methods have been described.6