The purpose of this study is to evaluate the efficacy and safety of the classic yin and yang tonic formula for osteopenia and to research the mechanism of efficacy.

Osteoporosis is a growing problem worldwide, with the greatest burden resulting from fractures. Nevertheless, the majority of fractures in adults occur in those with "osteopenia" (bone mineral density (BMD) only moderately lower than young normal individuals) Since life long drug therapy is an expensive option with uncertain consequences and side effect, natural herbal therapy offers an attractive alternative. The classic Yin and Yang Tonic Formula (eg.Zuogui Pill, Yougui Pill) have been used for osteoporosis or osteopenia in traditional Chinese medicine(TCM) for a long time. For this reason, Chinese guidelines for the treatment of osteopenia include natural herbal therapy, however, there is currently no randomize placebo controlled trial to verify the efficacy for treating low BMD. This trial is randomized, double blind, placebo controlled design. Results of this study will provide evidence regarding the value of the classic Yin and Yang tonic formula as an intervention for increase BMD and decreasing fracture risk in osteopenia. Furthermore, the mechanisms of action can be identified by this study.

Inclusion Criteria:

• BMD T-scores of the hip (femoral neck or trochanter)and/or spine between -1.0 and -2.5;
• pattern differentiation is kidney deficiency in TCM.
• informed consent.

Exclusion Criteria:

• Osteoporotic (T-score< -2.5) at any site or a fracture in the past 2 years not caused by motor vehicle accident;
• prior or current use of medication that increase risks of fracture (e.g. steroids, anti-convulsants, anticoagulants,lithium);
• prior or current use of medications that modify bone metabolism (e.g. bisphosphonates, selective estrogen receptor modulators such as Raloxifene);
• use of calcium supplements above levels suggested within the recommendations of standard care (i.e., above 1200-1500 mg);
• current or prior year use of estrogen or calcitonin;
• Malignancies other than skin cancer;
• conditions that cause secondary osteoporosis (e.g. Cushing's syndrome, Marfan's syndrome);
• lactation and gestational period;
• physical or mental disabilities that will preclude informed consent or active study participation;
• supersensitivity body constitution.
• osteoporotic fracture of having operating indication.