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Femara Side Effects

Generic Name: letrozole

Note: This page contains information about the side effects of letrozole. Some of the dosage forms included on this document may not apply to the brand name Femara.

In Summary

Common side effects of Femara include: bone fracture, edema, arthralgia, dizziness, fatigue, hypercholesterolemia, osteoporosis, and flushing. Other side effects include: myalgia. See below for a comprehensive list of adverse effects.

For the Consumer

Applies to letrozole: oral tablet

In addition to its needed effects, some unwanted effects may be caused by letrozole (the active ingredient contained in Femara). In the event that any of these side effects do occur, they may require medical attention.

Severity: Major

You should check with your doctor immediately if any of these side effects occur when taking letrozole:

Less common:
  • Bone fracture
  • breast pain
  • chest pain
  • chills, fever, or flu-like symptoms
  • mental depression
  • shortness of breath
  • swelling of the feet or lower legs
  • Continuing or severe nervousness
  • cough
  • dizziness or lightheadedness
  • fainting
  • fast heartbeat
  • heart attack
  • increased sweating
  • nausea
  • pain in the chest, groin, or legs, especially the calves
  • severe and sudden, unexplained shortness of breath
  • severe, sudden headache
  • slurred speech
  • sudden loss of coordination
  • sudden, severe weakness or numbness in the arm or leg
  • vaginal bleeding
  • vision changes
Incidence not known:
  • Black, tarry stools
  • blindness
  • blurred vision
  • burning, crawling, itching, numbness, prickling, "pins and needles", or tingling feelings
  • chest discomfort
  • decreased vision
  • dilated neck veins
  • extreme fatigue
  • increased need to urinate
  • irregular breathing
  • irregular heartbeat
  • painful or difficult urination
  • passing urine more often
  • sore throat
  • sores, ulcers, or white spots on the lips or in the mouth
  • swollen glands
  • unusual bleeding or bruising
  • unusual tiredness or weakness
  • weight gain
  • wheezing
  • white or brownish vaginal discharge

Severity: Minor

Some of the side effects that can occur with letrozole may not need medical attention. As your body adjusts to the medicine during treatment these side effects may go away. Your health care professional may also be able to tell you about ways to reduce or prevent some of these side effects. If any of the following side effects continue, are bothersome or if you have any questions about them, check with your health care professional:

More common:
  • Back pain
  • bone pain
  • hot flashes (sudden sweating and feeling of warmth)
  • joint pain
  • muscle pain
Less common:
  • Anxiety
  • confusion
  • constipation
  • diarrhea
  • dry mouth
  • headache
  • increased thirst
  • loss of appetite or weight loss
  • metallic taste
  • skin rash or itching
  • sleepiness
  • spinning or whirling sensation causing loss of balance
  • stomach pain or upset
  • trouble sleeping
  • vomiting
  • weakness
Incidence not known:
  • Bad, unusual, or unpleasant (after) taste and thirst
  • being forgetful
  • change in taste
  • dryness of the skin
  • hair loss
  • hives or welts
  • increased appetite
  • irritability
  • nervousness
  • red, sore eyes
  • redness of the skin
  • swelling or inflammation of the mouth

For Healthcare Professionals

Applies to letrozole: oral tablet


General side effects including fatigue (up to 8%), chest pain (up to 6%), peripheral edema (5%), asthenia (up to 5%), and increased weight (2%) have been reported.[Ref]


Cardiovascular side effects including hypertension (up to 7%), palpitations, cardiac failure, arterial thrombosis, angioedema, and tachycardia have been reported.[Ref]


Gastrointestinal side effects including nausea (up to 15%), vomiting (7%), constipation (up to 7%), diarrhea (up to 6%), abdominal pain (up to 6%), anorexia (up to 5%), dyspepsia (up to 4%), and dryness of mucosa (including dry mouth) have been reported.[Ref]


In the adjuvant setting, an increase in total cholesterol in patients who had baseline values of total serum cholesterol within the normal range, and then subsequently had an increase in total serum cholesterol of 1.5 time the upper limit of normal (ULN) was 5.4% on letrozole (the active ingredient contained in Femara) versus 1.2% on tamoxifen. Lipid lowering medications were used by 18% of patients on letrozole and 12% on tamoxifen.[Ref]

Other side effects including viral infection (up to 6%), dysesthesia, memory impairment, irritability, nervousness, stomatitis cancer pain, pyrexia, increased appetite and disturbances of taste and thirst have been reported.[Ref]


Musculoskeletal side effects including musculoskeletal effects in general (up to 22%) and arthralgia (up to 8%) have been reported. Postmarketing reports have included trigger finger.[Ref]

In the extended adjuvant setting, preliminary results (median duration of follow-up was 20 months) from the bone sub-study (calcium 500 mg and vitamin D 400 international units per day mandatory; bisphosphonates not allowed) demonstrated that at two years the mean decrease compared to baseline in hip bone mass density in letrozole patients was 3% versus 0.4% for placebo. The mean decrease from baseline bone mass density results for the lumbar spine at two years was letrozole 4.6% decrease and placebo 2.2%. Consideration should be given to monitoring bone mass density.[Ref]

Nervous system

Nervous system side effects including headache (up to 12%), somnolence (up to 3%), and dizziness (up to 5%) have been reported. Postmarketing reports have included carpal tunnel syndrome.[Ref]


Respiratory side effects including dyspnea (up to 9%) and coughing (up to 6%) have been reported.[Ref]


Dermatologic side effects including hot flushes (up to 6%), rash (up to 5%), pruritus (up to 2%), urticaria, and dry skin have been reported.[Ref]


Hepatic side effects including abnormal liver chemistries (3% in patients where it was not associated with a documented metastases) have been reported.[Ref]


Hematologic side effects including leukopenia and a case of reversible pancytopenia have been reported.[Ref]


Ocular side effects including cataract, eye irritation, and cases of blurred vision have been reported.


Metabolic side effects including hypercholesterolemia (3%) have been reported.[Ref]


Genitourinary side effects including increased urinary frequency and vaginal discharge have been reported.


Hypersensitivity side effects including anaphylactic reactions have been reported.


1. "Product Information. Femara (letrozole)." Novartis Pharmaceuticals, East Hanover, NJ.

2. Sperone P, Gorzegno G, Berruti A, Familiari U, Dogliotti L "Reversible pancytopenia caused by oral letrozole assumption in a patient with recurrent breast cancer." J Clin Oncol 20 (2002): 3747-8

Not all side effects for Femara may be reported. You should always consult a doctor or healthcare professional for medical advice. Side effects can be reported to the FDA here.

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