In most cases, a syndrome has more than one symptom that cannot be treated by one single herb. Thus, in Chinese herbal therapy, several herbs are used together in a formula in order to cope with the conditions of a disease. This is called compound therapy in Chinese medicine. Over the course of history, the Chinese have established more than 20,000 formulas, of which about 2,000 are currently in use. Although a physician of herbal therapy can use their own formulas to treat patients, established formulas have been proven effective in the past and should be used for clinical applications whenever possible.
A standard herbal formula consists of a king herb, subject herb, assistant herb, and servant herb. According to The Yellow Emperor's Classics of Internal Medicine, 'The primary herb in a formula is called the king herb, the herb included in the formula to assist the king herb is called the subject herb in that formula, and the herb included in the formula to be responsible to the subject herb is called the servant herb.'
Every formula must have at least a king herb, but not every formula needs a subject herb, an assistant herb, or a servant herb. Sometimes a formula may have a king herb that also plays the role of a subject herb, just like a prime minister may also act as the finance minister in a cabinet. As a general rule, the king herb in a formula has the largest dose, followed by the subject herb, the assistant herb, and the servant herb.
The king herb is the herb that is primarily responsible for dealing with the syndrome under treatment. For instance, if the patient has been diagnosed as suffering from the cold syndrome, the king herb must be capable of warming up the body. If the patient has been diagnosed as suffering from the kidney yang deficiency syndrome, the king herb must be capable of toning up the kidneys yang. Many formulas have more than one king herb, because a syndrome often contains two basic conditions that need to be treated simultaneously with two different herbs. Take the gallbladder dampness-heat syndrome, for example. This syndrome contains two basic conditions, namely, gallbladder-dampness and gallbladder-heat, so the formula selected to treat this syndrome may contain one herb to remove gallbladder-dampness and a second herb to clear gallbladder-heat.
The subject herb assists the king herb in two different ways: it reinforces the action of the king herb from a different angle and it treats the concurrent syndrome. For example, when the king herb in a formula is used to induce perspiration, a subject herb can be selected to produce body fluids to reinforce the function of the king herb in inducing perspiration. Sufficient body fluids will make perspiration easier, which means that the subject herb is helping the king herb achieve its objective indirectly. Another example is that when a person is suffering from two syndromes simultaneously, with one syndrome as the main one and the other syndrome as the concurrent one, the king herb will deal with the main syndrome while the subject herb will deal with the concurrent syndrome. As with king herbs, a formula can contain more than one subject herb.
The assistant herb in a formula can play one of the following three roles: it can assist the king herb or the subject herb in dealing with a relatively minor symptom, it can control the undesirable drastic actions of the king herb and the subject herb or reduce their toxic effects, and it can play the role of an opposition to supplement the action of the king herb.
In a formula, the servant herb plays two basic roles: it can direct the formula to the affected region and it can harmonze the herbs in the formula. The servant herb is typically used in small amounts, and its purpose is to harmonize and balance the actions of the other herbs in the formula. It can also act as a guide, directing the formula to the specific affected region in the body.
In summary, the king herb is the primary herb in a formula, responsible for treating the main condition of the syndrome. The subject herb reinforces the action of the king herb and treats the concurrent syndrome. The assistant herb assists with minor symptoms and controls undesirable actions or toxic effects. The servant herb directs the formula to the affected region and harmonizes the other herbs. By combining these different herbs in specific ratios, Chinese medicine practitioners can create formulas that are tailored to the individual needs of each patient.