What are SERMS?

Selective estrogen receptor modulators (SERMs) are medications that can both mimic and block estrogen’s effects in different tissues. They do this by interacting with estrogen receptors in different cells. SERMs are often used to treat estrogen-related conditions, such as infertility, osteoporosis, and some types of breast cancer.

Some people refer to SERMs as designer estrogen because they can offer many of estrogen’s benefits without some of its other effects. For example, they can help to prevent bone loss without stimulating the endometrial lining of the uterus.

Two of the most common SERMs are tamoxifen (Nolvadex, Soltamox) and raloxifene (Evista). There are several others as well, including lasofoxifene, bazedoxifene, and clomiphene citrate.

Keep reading to learn more about the types of SERMs and how they work to treat different conditions.

What are the benefits?

SERMs can be beneficial for many conditions. However, each SERM works differently, so your doctor will help you figure out which one will work best for your health.

For osteoporosis

Raloxifene is a common SERM used to help treat osteoporosis because it mimics estrogen’s beneficial effects on bone density. Studies suggest that it can increase bone density by in the lower spine and hips. Raloxifene may also reduce vertebral fractures by up to and lead to a decrease in other major fractures.

Bazedoxifene (FRAX) is another SERM that’s often used for osteoporosis and has effects similar to those of raloxifene.

For breast cancer

SERMs, particularly tamoxifen, are often used to help treat estrogen receptor-positive (ER-positive) breast cancer. This type of breast cancer involves cancer cells that have estrogen receptors just like normal breast cells. When estrogen binds to receptor sites in cancer cells, it makes them grow.

Tamoxifen works by sitting on the estrogen receptors in breast tissue. This prevents estrogen from binding to the cancer cells in the breast and making them grow. At the same time, it also acts as estrogen in the bones and uterus, where it has positive effects. It’s this ability to block estrogen in certain areas while activating it in others that makes SERMs selective.

For other conditions

Most SERMs are used by postmenopausal women. However, a SERM called clomiphene citrate (Clomid) can help to cause ovulation in premenopausal women dealing with infertility. It has an estrogen-like effect on the pituitary gland, which increases gonadotrophin activity. This increases the amount of follicle-stimulating hormone and luteinizing hormone in the ovaries, which both play important roles in ovulation and menstruation.

Some SERM combinations, such as bazedoxifene and conjugated estrogen, can also help to reduce uncomfortable menopause symptoms, such as vaginal dryness and hot flashes.

Are there any side effects?

Each type of SERM comes with its own list of possible side effects. Make sure to go over all the potential side effects with your doctor before starting a new SERM so you know what to watch for.

You may find that side effects are more noticeable in the first months of taking the drug.

While taking raloxifene, you may experience:

  • hot flashes
  • blood clots
  • white vaginal discharge
  • joint or muscle pain
  • feelings of depression
  • swelling at joints
  • difficulty sleeping
  • unexplained weight gain

side effects of raloxifene include:

  • coughing up blood
  • migraines
  • shortness of breath

Contact your doctor immediately if you notice any of these rarer symptoms.

Possible side effects of tamoxifen include:

  • reduced urination
  • hot flashes
  • menstrual changes
  • difficulty breathing or noisy breathing
  • redness on the face, neck, arms, or upper chest
  • skin changes
  • swelling of the fingers, hands, feet, or lower legs
  • weight changes
  • white or brown vaginal discharge

tamoxifen side effects include:

  • anxiety
  • blurred vision
  • chest pain
  • jaundice
  • rapid heartbeat
  • shallow breathing
  • dizziness

Tell your doctor right away if you notice any of these symptoms while taking tamoxifen.

There’s also some that tamoxifen may increase your risk of developing endometrial cancer.

Are they safe for everyone?

Most SERMs are made for postmenopausal women whose ovaries no longer produce estrogen. They’re not recommended for women who are pregnant or breastfeeding.

Tell your doctor about any blood clots or blood clotting disorders you have. SERMs may increase your risk of developing new ones and make existing clots worse. You should also tell them about any kidney or liver conditions. These can cause higher concentrations of SERMs in your blood.

You shouldn’t use SERMs if you have any of the following conditions:

  • congestive heart failure
  • heart rhythm problems, such as atrial fibrillation
  • high blood pressure
  • stroke
  • transient ischemic attack

The bottom line

SERMs are unique medications that can both block and mimic the effects of estrogen in different parts of your body. This makes them a valuable tool for helping to treat conditions like osteoporosis and ER-positive breast cancer. While they can cause some side effects, their benefits — such as reducing your risk of breast cancer or bone fractures — often outweigh them.