OsteoPorosis drugs. Sorry, and welcome to the party, Roger. You probably already know this:
osteoclasts are the cells that produce an acid to dissolve your bones so that the osteoblasts can fill all those acid-gaps with new bone. If you suddenly started playing tennis, for example, your arm bones would need to be able to withstand the impact from a different direction. The bones signal the osteoclasts and the osteoclasts signal the osteoblasts and they remodel the bone so that it doesn't break. It isn' t just new bone, its bone in which the strands (called spicules) line up in a direction that better withstands the pressure.
When you take a drug like alendronate (a bisphsophonate), you stop the remodel. Sadly, we do this just as we become aware that we need more exercise. So we challenge our bones with new activity while handicapping it's ability to cope with that exercise.
Even so, these drugs have prevented more fractures than they've caused. They work slowly because essentially they collect old bone and clad it.
I prefer the anabolic (bone building) middle age drugs (Forteo and Tymlos) especially for us older folk because they work faster and you end up with stronger, metabolically active bone.
Most of us consider estrogen, but you might consider testosterone.