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Femara (Letrozole) -- An Aromatase Inhibitor


Updated June 19, 2014

Femara (Letrozole) -- An Aromatase Inhibitor

Femara (letrozole)

Photo © Gold Standard

In a Nutshell:

Research has shown that Femara (letrozole) helps lower your risk of breast cancer recurrence, and improves your chance of survival.

Common Misspellings:

fimara, femarra, femera

Drug Type:

Femara is an antiestrogen, or aromatase inhibitor, like Aromasin. Femara is not a steroid.

How Femara Works to Prevent Breast Cancer Recurrence:

Many breast tumors are fueled by estrogen. Before menopause, your ovaries produce most of your estrogen. After menopause, the ovaries stop making estrogen, but your breast and fatty tissues use the enzyme aromatase to continue making this hormone.

Femara blocks aromatase, preventing estrogen production and lowering your hormone levels. If breast cancer cells are present in your system, they have much less chance to grow if they can’t get any estrogen. With low estrogen levels after adjuvant chemotherapy treatment for estrogen receptor-positive breast cancer, your risk of recurrence is cut by more than 50%.

Who Can Take Femara:

This drug is for women who have been diagnosed with estrogen receptor-positive breast cancer. A patient must have completed primary treatment and be in menopause. Pre-menopausal women can take Femara if their ovaries are chemically suppressed. Women who have had estrogen receptor-negative breast cancer will not benefit from this drug.

Common Side Effects:

Femara may cause these side effects:Call Your Doctor if You Have These Symptoms:
  • diarrhea
  • nausea or vomiting
  • unusual vaginal bleeding
  • difficulty breathing
  • chest pain
  • leg pain or swelling
  • skin rash


The temporary side effects of Femara are much more tolerable when you know that your risk of recurrence is greatly reduced. Women who took Femara after five years of Tamoxifen had significantly lower risk of recurrence that those who took a full five years of Tamoxifen. In addition, with Femara, your risk of a new cancer in the opposite breast is less than with Tamoxifen alone.

Available as:

  • 2.5 mg pill
  • brand name (no generic version available)
  • prescription only


Take Femara once a day with water. This drug does not have to be taken with food. Try to take it at the same time each day, to maintain an even level of the drug in your system. If you miss a dose, don’t double up, just wait till the next day and resume your medication schedule. Do not take this drug if you are still having menstrual periods or are pregnant.
Drugs That May Interact With Femara
Journal of Clinical Oncology. Late Extended Adjuvant Treatment With Letrozole Improves Outcome in Women With Early-Stage Breast Cancer Who Complete 5 Years of Tamoxifen. Paul E. Goss, et al. 10.1200/JCO.2007.11.6798.

National Cancer Institute. Drug Information. FDA Approval for Letrozole. Last Updated: 09/01/2006. Femara Label Information.

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