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Letrozole Side Effects

For the Consumer

Applies to letrozole: oral tablet

Along with its needed effects, letrozole may cause some unwanted effects. Although not all of these side effects may occur, if they do occur they may need medical attention.

Check with your doctor immediately if any of the following side effects occur while 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

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

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


Very common (10% or more): Hot flash/flushing (49.7%), cardiovascular disease (14.4%), other cardiovascular event (12.7%)
Common (1% to 10%): Hypertension, chest pain, cardiac event (angina, coronary heart disease, myocardial ischemia, myocardial infarction), cardiac failure
Uncommon (0.1% to 1%): Palpitation, tachycardia, arterial thrombosis[Ref]


Very common (10% or more): Nausea (17%), constipation (11.3%)
Common (1% to 10%): Vomiting, diarrhea, abdominal pain, dyspepsia
Uncommon (0.1% to 1%): Stomatitis, dry mouth[Ref]


Very common (10% or more): Fatigue/lethargy/malaise/asthenia (33.6%), edema (18.4%), night sweats (14.6%)
Common (1% to 10%): Influenza, peripheral edema, pain, post-mastectomy lymphedema, thromboembolic event, viral infection
Uncommon (0.1% to 1%): Pyrexia, mucosal dryness, thirst
Frequency not reported: Peripheral thromboembolic event (venous thrombosis, thrombophlebitis, portal vein thrombosis, pulmonary embolism)[Ref]


Very common (10% or more): Arthralgia/arthritis (25.2%), bone fracture (22%), musculoskeletal pain/back pain/arm pain/leg pain (22%), osteoporosis (14.5%), extremity/limb pain (10%)
Common (1% to 10%): Myalgia, bone pain, osteopenia, decreased lumbar spine bone mineral density
Postmarketing reports: Trigger finger[Ref]

Nervous system

Very common (10% or more): Headache (20.1%), dizziness/lightheadedness (14.2%)
Common (1% to 10%): Somnolence, cerebrovascular events (transient ischemic attack, thrombotic or hemorrhagic stroke, hemiparesis development)
Uncommon (0.1% to 1%): Memory impairment, dysesthesia (hypesthesia/paresthesia), taste and thirst disturbance, carpal tunnel syndrome
Rare (less than 0.1%): Cerebrovascular infarction
Frequency not reported: Vertigo[Ref]


Very common (10% or more): Dyspnea (18%), cough (13%)
Common (1% to 10%): Chest wall pain
Frequency not reported: Pleural effusion[Ref]


Very common (10% or more): Increased sweating (24.2%)
Common (1% to 10%): Alopecia, dry skin, rash (erythematous, maculopapular, psoriasiform, vesicular), pruritus
Uncommon (0.1% to 1%): Urticaria
Very rare (less than 0.01%): Angioedema, toxic epidermal necrolysis, erythema multiforme[Ref]


Uncommon (0.1% to 1%): Increased hepatic enzymes
Very rare (less than 0.01%): Hepatitis[Ref]


Uncommon (0.1% to 1%): Leukopenia
Frequency not reported: Decreased lymphocyte count, thrombocytopenia[Ref]


Common (1% to 10%): Cataract
Uncommon (0.1% to 1%): Eye irritation, blurred vision[Ref]


Very common (10% or more): Hypercholesterolemia (52.5%), increased weight (12.9%)
Common (1% to 10%): Decreased weight, anorexia, increased appetite
Frequency not reported: Hypercalcemia[Ref]


Very common (10% or more): Vaginal bleeding (12.7%)
Common (1% to 10%): Vaginal irritation, vaginal hemorrhage, vulvovaginal dryness, breast pain, urinary tract infection
Uncommon (0.1% to 1%): Increased urinary frequency, vaginal discharge[Ref]


Very rare (less than 0.01%): Anaphylactic reactions[Ref]


Common (1% to 10%): Secondary malignancy
Uncommon (0.1% to 1%): Endometrial hyperplasia/cancer, endometrial proliferation disorder, tumor pain
Rare (less than 0.1%): Other endometrial disorder
Frequency not reported: Stomatitis cancer pain[Ref]


Common (1% to 10%): Depression, insomnia
Uncommon (0.1% to 1%): Anxiety, nervousness, irritability[Ref]


Common (1% to 10%): Renal disorders[Ref]


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

2. Cerner Multum, Inc. "UK Summary of Product Characteristics." O 0

3. Cerner Multum, Inc. "Australian Product Information." O 0

Some side effects of letrozole may not be reported. Always consult your doctor or healthcare specialist for medical advice. You may also report side effects to the FDA.

Disclaimer: Every effort has been made to ensure that the information provided is accurate, up-to-date and complete, but no guarantee is made to that effect. In addition, the drug information contained herein may be time sensitive and should not be utilized as a reference resource beyond the date hereof. This material does not endorse drugs, diagnose patients, or recommend therapy. This information is a reference resource designed as supplement to, and not a substitute for, the expertise, skill , knowledge, and judgement of healthcare practitioners in patient care. The absence of a warning for a given drug or combination thereof in no way should be construed to indicate safety, effectiveness, or appropriateness for any given patient. does not assume any responsibility for any aspect of healthcare administered with the aid of materials provided. The information contained herein is not intended to cover all possible uses, directions, precautions, warnings, drug interactions, allergic reactions, or adverse effects. If you have questions about the substances you are taking, check with your doctor, nurse, or pharmacist.