Have you heard of designer estrogens? They are not really estrogens at all, but chemical compounds that may act like estrogen in some parts of the body, but an anti-estrogen in another part of the body.
Let's talk science. We know that estrogens have an effect on almost all organs of the body. Estrogens attach to an estrogen receptor in some organs, thereby 'turning on' that cell to allow a certain function. Other chemical compounds can attach to the receptor and turn it off. SERM's, or selective estrogen receptor modulators, are not hormones at all, but have an effect on the estrogen receptor. In some organs there can be a positive effect, and is other organs a negative effect.
Tamoxifen is a SERM that is used in breast cancer patients to decrease recurrence. It attaches to the estrogen receptor in the breast and and prevents estrogen from stimulating breast tissue. Tamoxifen has a stimulatory effect in the uterus and can lead to uterine cancer, and it does increase hot flashes.
Raloxifene is a SERM that is used to prevent osteoporosis. It has a beneficial effect on the bones, acting like an estrogen. However, in the breast, it acts like an anti-estrogen and decreases breast cancer up to 50% in women who take it for about 5 years. Hot flashes and blood clots are side effects.
Ospemifene is a SERM that can act as an estrogen in the vaginal tissue. It increases vaginal moisture. It's effect on the breast has not bee studied.
Bazedoxifene is a SERM that has been combined with estrogen to treat hot flashes. The benefit of this combination is that no progesterone is needed, and there is less bleeding that is seen with estrogen and progesterone. Baxedoxifene combined with conjugated estrogen decreases menopausal symptoms, prevents bone loss, and does not increase the risk of uterine cancer.
The story of SERM's is great basic science. These drugs can be life-changing in many women, and your doctor can determine if one of them fits your needs.