Chapter 33 Botanical Medicine—A Modern Perspective
The term herb refers to a plant used for medicinal purposes. Are herbs effective medicinal agents or is their use merely a reflection of folklore, outdated theories, and myth? To the uninformed, herbs are generally thought of as ineffective medicines used before the advent of more effective synthetic drugs. To others, herbs are simply sources of compounds to isolate and then market as drugs. However, to some, herbs and crude plant extracts are effective medicines to be respected and appreciated.
For many people of the world, herbal medicines are the only therapeutic agents available. In the late 1990s, the World Health Organization estimated that about 80% of the world’s population relies on herbs for primary health care needs.1 This widespread use of herbal medicines is not restricted to developing countries, since it has been estimated that 70% of all medical doctors in France and Germany regularly prescribe herbal preparations.
Although herbal medicine has existed since the dawn of time, knowledge of how plants actually affect human physiology remains largely unexplored. Many individuals formulate their view of herbal medicine based on opinion, philosophy, and ideology. This chapter seeks to facilitate an informed view of herbal medicine. The past and future of herbal medicines are discussed. We believe that the continued evolution of the tradition of herbal medicine can only be accomplished within the context of continued scientific investigation.
Throughout the world, but especially in Europe, the United States, Canada, Australia, and Japan, a tremendous renaissance in the use and appreciation of herbal medicine occurred in the latter part of the twentieth century. For example, in the United States, the sale of herbal products skyrocketed from $200 million in 1988 to more than $3.5 billion in 1997 before leveling off in the $4 billion a year range (Table 33-1). Within the European Community annual sales exceeded $7 billion in 1997.2
|YEAR||$ TOTAL SALES (MILLIONS)||% INCREASE (-DECREASE)|
Data from Ferrier GKL, Thwaites LA, Rea PR, et al. U.S. consumer herbal and herbal botanical supplement sales. Nutr Business J. 2006. http://www.nutritionbusiness.com.
The rebirth of herbal medicine, especially in developed countries, is largely based on a renewed interest by the public and scientific researchers. During the past 20 to 30 years, there has been a huge increase of scientific information concerning plants, crude plant extracts, and various substances from plants as medicinal agents. For example, a PubMed search of the term “herbal medicine” yielded over 1300 hits in 2010. However, the number of studies of botanical medicines is much higher. For example, there were 130 studies published on Ginkgo biloba alone in 2010.
Plants still play a major role in modern pharmacy. For the past 50 years, about 25% of all prescription drugs in the United States and other developed countries have contained active constituents obtained from plants. Digoxin, codeine, colchicine, morphine, vincristine, and yohimbine are some popular examples. Many over-the-counter (OTC) preparations are also composed of plant compounds. Pharmacognosy, the study of natural drugs and their constituents, plays a major role in current drug development. Unfortunately, the standard path of the approval of a drug is a process that typically takes 10 to 18 years at a total cost of roughly $250 million (Table 33-2).
|DRUG||CLINICAL USE||BOTANICAL SOURCE|
|Caffeine||Central nervous system stimulant||Cola nitida|
|Cocaine||Local anesthetic||Erythroxylon coca|
|Gossypol||Male contraceptive||Gossypium spp.|
|Physostigmine||Cholinesterase inhibitor||Physostigma venenosum|
|Podophyllotoxin||Topical wart remedy||Podophyllum peltatum|
|Tubocurarine||Muscle relaxant||Chondrodendron tomentosum|
|Yohimbine||Male erectile dysfunction||Pausinystalia yohimbe|
Data from De Smet PA. Drugs 1997;54:801-840.
Because a plant cannot be patented, plants are screened for biological activity and then the so-called “active” constituents (compounds) are isolated and typically chemically modified to produce unique substances. If the compound is powerful enough, the drug company begins the process to procure Food and Drug Administration (FDA) approval. Of 520 new drugs approved by the FDA or comparable entities in developed countries, 30 came directly from natural product sources and another 173 were either semisynthetic from a natural source or modeled after a naturally occurring compound.1
Because of the expense and lack of patent protection, few clinical evaluations were done before 1980 on whole plants or crude plant extracts as medicinal agents per se. A key factor in contributing to more research into herbal medicines after this time was the development in Europe of regulatory policies and practices that made it economically feasible for companies to do research. For example, in Germany, regulations allow herbal products to be marketed with drug claims if they are proven to be safe and effective.3 Whether the herbal product is available by prescription or OTC is based on its application and safety of use. Herbal products sold in pharmacies are reimbursed by insurance if they are prescribed by a physician.
The proof required by a manufacturer in Germany to illustrate safety and effectiveness for an herbal product is less (and more appropriate) than the proof required by the FDA for drugs in the United States. In Germany, a special commission (Commission E) developed a series of 400 monographs on herbal products similar to the OTC monographs in the United States. A herbal product is viewed as safe and effective if a manufacturer meets the quality requirements of the monograph or produces additional evidence of safety and effectiveness that can include data from existing literature, anecdotal information from practicing physicians, and limited clinical studies. In contrast, in the United States, extracts that are identical to those approved in Germany as drugs are available as “dietary supplements,” yet manufacturers are prohibited from making any therapeutic claims for their products. No medicinal claims are allowed for most herbal products in the United States because the FDA requires the same standard of absolute proof as required for new synthetic drugs. Thus far, the FDA has rejected the idea of establishing an independent “expert advisory panel” for the development of monographs similar to Germany’s Commission E monographs, as well as other ideas to create a suitable framework for the marketing of herbal products in the United States.
The monograph system in Germany allowed companies to market their products according to the guidelines of Commission E. With the ability to make appropriate claims, many companies achieved success with their products and were enabled to fund the necessary research to gain greater acceptance within mainstream, conventional medicine. The use of St. John’s wort extract in the treatment of depression is a perfect case in point to illustrate how Commission E monographs led to significant documentation of the efficacy of plants with a long history of folk use for depression.
When the Commission E monograph for St. John’s wort came out in 1984, it identified the constituent hypericin as the active constituent and permitted the medicinal use of the herb (in average doses of 2 to 4 g of herb, or 0.2 to 1 mg total hypericin) for depression, anxiety, or nervous excitement.
Originally, it was thought that hypericin acted as an inhibitor of the enzyme monoamine oxidase, thereby resulting in the increase of central nervous system monoamines such as serotonin and dopamine. However, it was later shown that St. John’s wort does not inhibit monoamine oxidase in vivo.4 The antidepressant activities appear to be related more to serotonin reuptake inhibition as occurs with the drugs Prozac, Paxil, and Zoloft; modulation of neuroendocrine function; downregulation of β-adrenergic receptors; and upregulation of serotonin receptors in the brain areas that are implicated in depression.4,5 In addition, it appears that although hypericin is an important marker, other compounds such as flavonoids are also thought to play a major role in the pharmacology of St. John’s wort. The key point here is that the further understanding and documentation of clinical effectiveness of St. John’s wort extract was largely the direct result of a commercial incentive created by the existence of Commission E.6
Improvements in analytic techniques and modern pharmacology have given researchers the tools and understanding necessary to evaluate herbal medicines properly. Improvements in plant cultivation techniques and the quality of herbal extracts (quality control and standardization) have also led to the development of some effective plant medicines. These advances have created a renaissance in the appreciation and use of herbal medicine. It seems that science and medicine have finally advanced to a level where nature can be appreciated rather than discounted. The scientific investigation of plant medicines is replacing some of the mystery and romance of herbalism with a greater understanding of the ways in which herbs work. Thirty years ago it was impossible to determine exactly how herbs promoted their healing effects because analytic science had not advanced to a sufficient level of sophistication. This point is well illustrated by the fact that the main mechanism of action responsible for aspirin’s anti-inflammatory effect was not understood until the early 1970s, and its mechanism of action for pain relief has yet to be fully understood.
Because the mechanism of therapeutic action of a particular herb could not be fully elicited, many effective plant medicines were erroneously labeled as possessing no pharmacologic activity. Now, researchers equipped with greater understanding and more sophisticated technology are rediscovering the wonder of plants as medicinal agents. Much of the increased understanding is, interestingly, a result of synthetic drug research.
For example, one of the modern classes of drugs is calcium channel blockers. These agents block the entry of calcium into smooth muscle cells, thereby inhibiting contraction and promoting muscular relaxation. Calcium channel blocking drugs are currently being used in the treatment of high blood pressure, angina, asthma, and other conditions associated with smooth muscle contraction. They represent a highly evolved stage of modern drug pharmacy. After calcium channel drugs became better understood, it was discovered that many herbs contain components that possess calcium channel blocking activity. In most cases, the historical use of these herbs corresponded to their calcium channel blocking activity.
In addition to possessing currently understood pharmacologic activity, many herbs possess pharmacologic actions that are not consistent with modern pharmacologic understanding. For example, often an herb appears to affect homeostatic control mechanisms to aid normalization of many bodily processes. When there is a hyperstate, the herb has a lowering effect, and when there is a hypostate, it has a heightening effect. This action is totally baffling to orthodox pharmacologists, but not to experienced herbalists who have used terms such as alterative, amphoteric, adaptogen, or tonic to describe this effect.