Chinese herbalism dates back to 2852 B.C. More than 2,600 herbs and thousands of herbal formulae are used to treat illness. Classical theories of Chinese medicine are integrated with the Taoist philosophy, whereby the universe is composed of two basic forces: a positive one called yang, and a negative one called yin. Illness is thought to occur when there is too much yang (tonification) or too much yin (sedation) in the body and herbal medicines are therefore intended either to tonify or to sedate the body so that balance is restored. Since 1954, some Chinese herbal remedies have been scientifically analyzed and tested. Several have been proven effective in treating a variety of diseases and conditions.