What is Alendronate? Alendronic acid (INN) or alendronate sodium (USAN) — sold as Fosamax by Merck. Alendronate is used in men and women to treat or prevent osteoporosis caused by menopause or by taking steroids. Alendronate is also used to increase bone mass in men who have osteoporosis, and to treat Paget’s disease of bone in men and women. Alendronate may also be used for purposes not listed in this medication guide.