Chinese Herbal medicine is  still  new  to western world and they don't know whether it is safe or not.   When we say "Chinese herb" , we are talking about single  herb or herb formula. 

Generally speaking, about 95% of an herb (crude dried herb as appears in Chinese pharmacies) is medicinally inactive and comprised of carbohydrate materials such as cellulose, starch, and simple sugars; fats, such as heavy oils and simple fatty acids; and proteins, mostly complex structural proteins and enzymes with some free amino acids. In addition, there are vitamins, minerals, and other compounds that are typical of what is found ordinary foods. The presence of these ordinary substances, some of which are removed when making extracts, are the reason why the dosage of herbs needs to be so high compared to drug therapies.

About 5% of an herb, often less, is comprised of some active compounds that are either different from those found in foods, or similar to those found in foods but in larger quantities. These mainly fall into the following groups:

1. Terpenes (subdivided into mono-, di-, tri-, and sesqui-terpenes); virtually all of these are safe compounds that promote circulation and calm agitation. As an example, the triterpenes of ginseng, zizyphus, bupleurum, and ganoderma can be consumed in quantities of several hundred milligrams to safely provide circulation-promoting and sedative effects.
   
   
2. Flavonoids (subdivided into flavones, isoflavones, anthocyanidins, etc.); virtually all of these are safe compounds that promote circulation and alleviate allergy reactions. As an example, the flavonoids in ginkgo leaf, pueraria, and citrus are known to have these effects and are used in doses of several hundred milligrams.
   
   
3. Pyrones, quinones, and other oxygenated compounds; virtually all of these are safe compounds that promote circulation and alleviate spasms and pain. As examples, the benzopyrones of tang-kuei, cnidium, and chiang-huo and the quinones of salvia are all used to aid circulation and relieve pain, and are used in doses of several hundred milligrams.
   
   
4. Alkaloids; several alkaloids have the potential for significant adverse effects, because alkaloids often interact with the nervous system. However, Chinese herbs that rely on alkaloids are often selected because of their mild activity; most have antibacterial, fever reducing, and sedative effects. Examples are coptis, phellodendron, and sophora; even these herbs can have adverse effects if the dosage is too high and if the administration of high doses is continued over a long period. Nonetheless, the alkaloids of these herbs are often consumed in quantities of several hundred milligrams per day without adverse reactions.

Herb can usually be taken while the amount of active components consumed remain within the hundreds of milligrams that are safe and without any significant adverse effects. Chinese herbs that have significantly toxic compounds, such as strychnos, datura, raw aconite, and croton, are not incorporated into the Western practice of traditional Chinese medicine.

Also in the formula, always  the herb combination  was selected to minimize the side effects or relieve toxicity. Comparing the side effects of  western medicine drug, Chinese herbs are known to be safe.