Bisphosphonates are widely used globally as the main treatment for osteoporosis. Both safety and efficacy have only been rigorously evaluated in studies of relatively short duration (3-5 years), with smaller extension studies. The evidence for benefit beyond five years in intervention studies is limited and does not include proven efficacy against nonvertebral fractures. Observational studies suggest a sustained benefit against hip fractures. Bisphosphonates are stored in the skeleton for months to years, depending on the degree of bone turnover and the binding properties of the bisphosphonate in question. The effects of continued treatment on bone strength is not known but there are concerns that osteonecrosis of the jaw and atypical femur fractures may stem from long term bisphosphonate use.