This Comparative Effectiveness Review (CER) compares the benefits in fracture reduction and the harms from adverse events (AE) among and within the various classes of treatment for low bone density. Our outcomes of interest for measuring benefits are vertebral, non-vertebral, hip, and radial fractures. The studies collect vertebral fracture outcomes in one of two ways. In some studies, all participants undergo radiography at pre-determined intervals. Other studies use clinical criteria, i.e. whether a fracture has been diagnosed by a clinician during the time interval. Trials that radiograph all participants will by nature detect more fractures. However the higher detection rate will apply to both treatment and placebo groups. Thus, the relative differences found should be similar that found in studies that use clinical criteria.