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

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
• 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

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

Applies to letrozole: oral tablet

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

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

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)

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

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

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

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

Frequency not reported: Pleural effusion

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

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

Very rare (less than 0.01%): Hepatitis

Uncommon (0.1% to 1%): Leukopenia

Frequency not reported: Decreased lymphocyte count, thrombocytopenia

Common (1% to 10%): Cataract

Uncommon (0.1% to 1%): Eye irritation, blurred vision

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

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

Frequency not reported: Hypercalcemia

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

Very rare (less than 0.01%): Anaphylactic reactions

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

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

Uncommon (0.1% to 1%): Anxiety, nervousness, irritability

Common (1% to 10%): Renal disorders