By Ken Rose, Co-author Who Can Ride The Dragon?
Herbal medicine is the mainstay of traditional Chinese medicine. Its origins date to prehistoric times. It reflects ancient, agrarian cultural values as well as knowledge about the nature of plants and animals in the environment and their use as medicinals. In time, a lore accumulated that was passed from generation to generation. After centuries of such transmission, the knowledge of herbal ingredients became distilled and refined.
As in many other areas of Chinese life, significant refinements took place over a period of some 1,500 years between the middle of the first millennium BCE and the end of the first millennium CE. We find the basic theories of herbal medicine already well developed in texts that date to the second century BCE discovered at Ma Wang Dui in Chang Sha in Hunan province.
By the Tang dynasty (618 - 906 C.E.) the theory and practice of herbal medicine in China had become an elaborate and effective art and science. By the Song-Jin-Yuan periods herbs were classified according to their flavor, temperature, nature, and functions within the body. This system of classification was based upon the theory of yin and yang. It included a correlation of herbs with the various internal organs and their interconnecting pathways of circulation (zang fu and jing luo q.v.) according to a grand scheme of systematic correspondences (q.v.). This theory underlies and unifies Chinese medical theory into a comprehensive system of medical procedures that can be adapted to a wide variety of conditions (See: Scientific Research - conditions treated by Chinese medicine at this site). 
Perhaps more importantly, the art of herbal medicine has always been intimately linked with the art and science of macrobiotics or life extension in China. Herbs are first and foremost foodstuffs that nourish the body in precise and well-defined ways. The lore of Chinese herbal medicine is vast and occupies literally thousands of ancient classics.
In the West we have only scraped the surface of this vast literature, but with a growing number of people hungry for herbal medicine, we will no doubt witness an increase in the appearance of such information over the years to come.
Can one self-prescribe Chinese herbal medicine with good results?
In China, where knowledge of Chinese herbs is widespread, people frequently self-prescribe herbal medicines for common complaints. But even in China, whenever there is a severe medical condition, people seek out the guidance of a properly trained practitioner. Herbal medicines, though notably free of side effects as a general rule, can produce unwanted results. There are eighteen herbs that strictly must not be combined, for example, and there are other key
data that govern the effective use of herbal medicines. Without proper training in the subject, one cannot expect the best results. The rule of thumb is to consult a well-trained practitioner and follow his or her recommendations.
We've all heard horror stories resulting from misuse of herbal ingredients. What are the dangers associated with the use of Chinese medicinal herbs?
There are dangers associated with all medical interventions. These range from lack of effects, resulting in worsening of the condition to the appearance of harmful even fatal side effects. This whole range of dangers definitely applies to the use of herbal medicines and thus they should not be taken lightly. From a statistical point of view, however, far fewer people suffer unwanted side effects from medicinal herbs than from powerful modern pharmaceuticals. Some 80,000 people a year die in hospitals from a variety of iatrogenic factors. The proper use of herbal medicines can be an important factor in keeping people healthier and therefore out of harm's way in hospitals.
Are there adulterants in imported herbal preparations?
Yes. One must be extremely careful when selecting pre-formulated packaged herbs, often known as `patent formulas ' (zhong cheng yao, in Chinese). Some such herbal preparations contain heavy metals (such as mercury, known as cinnabar in herbal terms, lead, and others). Still others may contain prescription medicines that are not listed on the label. One must proceed with knowledge and care.
How can someone know they're buying quality herbs?
The quality, even the identification of medicinal herbs is an old problem indeed. The only way one can be certain is to invest the time to learn about the individual herbs so that they can be recognized and differentiated according to quality. Lacking this, one must rely upon properly trained practitioners. In short, one should not proceed with the use of medicinal herbs without a well-trained herbal practitioner to prescribe and provide quality herbs.