How does estrogen strengthen your bones? Basically, estrogen hinders osteoclasts, and helps osteoblasts. Estrogen slows the amount of bone osteoclasts can absorb; and it increases the amount of calcium osteoblasts (the “good guys”) can absorb. So bone breakdown is slowed, and the pace of bone buildup is increased.

Sounds good, right? Well, yes and no. Estrogen definitely helps slow/reverse osteoporosis. It’s also been identified as a significant breast cancer risk factor. So the use of HRT for osteoporosis has declined.

Calcitonin: This is a manufactured version of a naturally occurring hormone, and it comes in two brands: Fortical®, and Miacalcin®.

And how does it work? Exactly like bisphosphonates: by slowing the work of those bone-destroying osteoclasts, and (perhaps) encouraging osteoblasts to increase the pace of bone buildup.

Selective estrogen receptor modulators (SERMs): This type of drug has a split personality: in some parts of the body it acts like estrogen, while in others, it doesn’t. Evista (raloxifene) is the SERM most commonly prescribed for osteoporosis.

So what’s with the seemingly opposite effect SERMS have in different parts of your body? Why is that important? As mentioned above, estrogen is great for building bones. Unfortunately, for women with breast cancer (or those at identified high risk of getting it), estrogen is a no-no; it encourages breast cancer growth. Evista acts like estrogen on the bones, yet at the same time isn’t recognized as estrogen by breast tissue. Thus it helps bones, but doesn’t encourage breast cancer; a win-win for women.

Tamoxifen, a drug taken for over 30 years by breast cancer patients, is another common SERM. Its ability to build bone isn’t as great as that of raloxifene (Evista). Another promising option, bazedoxifene (Viviant), appears comparable to Evista, but it hasn’t yet been given FDA approval.

Whew, are you still with me? Congratulations! I hope you now know a bit more than you did about osteoporosis drugs, and how they work. In future posts, I’ll break this all down to more specific levels.