What Are Aromatase Inhibitors?

This group of drugs lowers levels of estrogen in the body.

Aromatase inhibitors are a class of drugs that reduce the production of estrogen in the body.

They work by stopping an enzyme called aromatase from turning other hormones into estrogen.

Examples of aromatase inhibitors include:

• Femara (letrozole)
• Arimidex (anastrozole)
• Aromasin (exemestane)

Each drug comes as a pill that is typically taken once a day. All three medications are available in generic form.

Why Are Aromatase Inhibitors Given?

Even though both women and men need estrogen, estrogen can cause problems by promoting the growth of estrogen-receptor-positive cancers, especially breast cancer.

Aromatase inhibitors are often used in addition to other to cancer treatments (such as surgery, radiation, and chemotherapy) to starve these estrogen-receptor-positive cancers of estrogen.

These drugs are also sometimes used to help with certain fertility problems, and to block the effects of estrogen in men with a condition called gynecomastia, which causes enlarged breast tissue.

How Do Aromatase Inhibitors Work?

Men and women both have "masculine" androgen hormones and "feminine" estrogen hormones, but in different concentrations.

The aromatase enzyme converts androgen hormones (testosterone and androstenedione) into estrogen hormones (estradiol and estrone).

Blocking the effects of aromatase reduces the amount of androgens converted into estrogens.

In women before menopause, most estrogen hormones are made in the ovaries.

Aromatase inhibitors don't work to lower estrogen if your ovaries are still functioning. These drugs are only given to women who have gone through menopause, or who have had treatment to suppress the normal functioning of their ovaries.

You shouldn't take aromatase inhibitors if you're pregnant or breastfeeding.

Aromatase Inhibitors for Cancer Treatment

Aromatase inhibitors are given to postmenopausal women with estrogen-receptor-positive cancers, particularly of the breast.

They're taken long-term, for 3 to 5 years or even longer.

Another class of drugs, called selective estrogen receptor modulators (SERMs), is used similarly. SERM drugs include Soltamox (tamoxifen) and Evista (raloxifene).

In postmenopausal women with estrogen-receptor-positive breast cancer, aromatase inhibitors have been found to be more effective and have fewer side effects than SERMs.

Other Uses for Aromatase Inhibitors

Aromatase inhibitors are also used for the following purposes:

Treating unwanted side effects of testosterone: Because some of the circulating testosterone is converted into estrogen by aromatase, men who take extra testosterone may develop breasts, experience undesired fat deposits, or have fertility problems.

Although they're not approved for this purpose, aromatase inhibitors are sometimes also taken by anabolic-androgenic steroid (AAS) users to prevent certain side effects of their use.

Increasing fertility in polycystic ovary syndrome (PCOS): Some studies have shown that aromatase inhibitors may help premenopausal women with polycystic ovary syndrome carry a pregnancy to term.

Lowering the risk of breast cancer: Some studies have shown that taking aromatase inhibitors can lower the risk of breast cancer in women who are at high risk, but these drugs aren't currently approved for this purpose in the United States.

Side Effects of Aromatase Inhibitors

Aromatase inhibitors can have certain unwanted side effects, including:

Weakening of the bones: These drugs may increase the risk of fractures and osteoporosis.

You may want to ask your doctor for a vitamin D level test and bone density scan (also called DEXA or bone densitometry) before taking these medications, and every 1 to 2 years while taking them.

Your doctor may want recommend performing weight-bearing exercises or taking calcium and vitamin D supplements to strengthen your bones.

If your bones do become weak, your condition may be treated with a class of drugs called bisphosphonates.

Joint pain and bone pain: This pain can be severe enough for some people to stop taking their medication.

If your pain persists, you may want to ask your doctor whether you need an X-ray to check for a broken bone.

Menopausal symptoms: These symptoms may include hot flashes, night sweats, and decreased libido. A group of antidepressants called selective serotonin reuptake inhibitors (SSRIs) may help with some of these symptoms.

For vaginal health issues like atrophy and dryness, talk to your doctor about your treatment options if personal lubricants don't solve the problem.