i was checked and had osteoporosis at age 43. a couple of years of Fosamax increased my bone density, and i haven't taken it since.
bone density last year was okay, but i've been thinking i'd like to take fosamax again for prevention and to try to build some more bone. I have read you need magnesium for calcium absorption, hard to find.
There is evidence that one course of Fosamax (or drugs in its class--the bisphosphonates) does it for a long long time.