It certainly can be confusing and frustrating. My understanding is that bone continues to remodel (remove old bone tissue and form new bone tissue) until death. But as you age the balance changes until resorption out paces formation. this change leads to bone loss and increased risk of osteoporosis. Alendronate and prolia slow down the breakdown of bone , but by different means, allowing the body to build up more bone density. I am sorry to hear of your bad reaction to fosamax. my endo gave me a choice of fosamax and prolia. I've taken fosamax for 8 months now with no issues, but if i couldn't tolerate it i would give prolia a chance.