Letrozole Side Effects

Medically reviewed by Philip Thornton, DipPharm. Last updated on Jan 28, 2024.

Applies to letrozole: oral tablet.

Serious side effects of Letrozole

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
• swelling of the feet or lower legs

Rare

• 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 troubled breathing
• severe, sudden headache
• slurred speech
• sudden loss of coordination
• sudden, severe weakness or numbness in the arm or leg
• swollen glands
• 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
• dark urine
• decreased vision
• dilated neck veins
• extreme tiredness or weakness
• general tiredness or weakness
• increased need to urinate
• irregular breathing
• irregular heartbeat
• light-colored stools
• painful or difficult urination
• passing urine more often
• sore throat
• sores, ulcers, or white spots on the lips or in the mouth
• unusual bleeding or bruising
• unusual tiredness or weakness
• upper right abdominal pain
• weight gain
• white or brownish vaginal discharge
• yellow eyes and skin

Other side effects of Letrozole

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.

Cardiovascular

Very common (10% or more): Hot flash/flushing (50%), cardiovascular disease (14%), other cardiovascular event (13%)

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]

Gastrointestinal

Very common (10% or more): Nausea (17%), constipation (11%)

Common (1% to 10%): Vomiting, diarrhea, abdominal pain, dyspepsia

Uncommon (0.1% to 1%): Stomatitis, dry mouth^[Ref]

Other

Very common (10% or more): Fatigue/lethargy/malaise/asthenia (34%), edema (18%), night sweats (15%)

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]

Musculoskeletal

Very common (10% or more): Arthralgia/arthritis (25%), bone fracture (22%), musculoskeletal pain/back pain/arm pain/leg pain (22%), osteoporosis (15%), 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%), dizziness/lightheadedness (14%)

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]

Respiratory

Very common (10% or more): Dyspnea (18%), cough (13%)

Common (1% to 10%): Chest wall pain

Frequency not reported: Pleural effusion^[Ref]

Dermatologic

Very common (10% or more): Increased sweating (24%)

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]

Hepatic

Uncommon (0.1% to 1%): Increased hepatic enzymes

Very rare (less than 0.01%): Hepatitis^[Ref]

Hematologic

Uncommon (0.1% to 1%): Leukopenia

Frequency not reported: Decreased lymphocyte count, thrombocytopenia^[Ref]

Ocular

Common (1% to 10%): Cataract

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

Metabolic

Very common (10% or more): Hypercholesterolemia (53%), increased weight (13%)

Common (1% to 10%): Decreased weight, anorexia, increased appetite

Frequency not reported: Hypercalcemia^[Ref]

Genitourinary

Very common (10% or more): Vaginal bleeding (13%)

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]

Hypersensitivity

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

Oncologic

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]

Psychiatric

Common (1% to 10%): Depression, insomnia

Uncommon (0.1% to 1%): Anxiety, nervousness, irritability^[Ref]

Renal

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

Frequently asked questions

• How long do letrozole side effects last?
• What happens when you stop taking letrozole?
• When is the best time of day to take letrozole?
• How many cycles of letrozole are needed to get pregnant?
• Is letrozole a form of chemotherapy?
• Does letrozole affect blood sugar levels?
• When will I ovulate after taking letrozole?
• How do you take letrozole for fertility?
• How does Femara affect your period?

Further information

Always consult your healthcare provider to ensure the information displayed on this page applies to your personal circumstances.

Some side effects may not be reported. You may report them to the FDA.

Medical Disclaimer