In the U.S.—

In Canada—

• Antineoplastic

Letrozole (LET-roe-zole) is used to treat certain types of breast cancer in women. Female hormones that occur naturally in the body can increase the growth of some breast cancers. Letrozole works by decreasing the amounts of these hormones in the body. This medicine is meant to be used only by women who have already stopped menstruating.

This medicine is available only with your doctor's prescription, in the following dosage form:

Oral
• Tablets (U.S. and Canada)

In deciding to use a medicine, the risks of taking the medicine must be weighed against the good it will do. This is a decision you and your doctor will make. For letrozole, the following should be considered:

Allergies—Tell your doctor if you have ever had any unusual or allergic reaction to letrozole. Also tell your health care professional if you are allergic to any other substances, such as foods, preservatives, or dyes.

Pregnancy—This medicine is meant to be used only by women who are no longer able to have children. If this medicine is taken by a pregnant woman for any reason it may cause harm to, and possibly even death of, the fetus.

Older adults—This medicine has been tested and has not been shown to cause different effects in older women than in younger adults.

• Kidney disease or
• Liver disease—Problems are not likely to occur in people with mild kidney or liver disease. However, it is not known whether severe kidney or liver disease may increase the chance of side effects during treatment

Take this medicine only as directed by your doctor. Do not take more of it, and do not take it more often than your doctor ordered.

Dosing—

The dose of letrozole may be different for different patients. Follow your doctor's orders or the directions on the label. The following information includes only the average dose of letrozole. If your dose is different, do not change it unless your doctor tells you to do so.

• For oral dosage form (tablets):
  • For breast cancer:
    • Adults—One 2.5–milligram tablet a day.

Missed dose—

If you miss a dose of this medicine, take it as soon as you remember. However, if you do not remember until the next day, skip the missed dose and go back to your regular dosing schedule. Do not double the next day's dose.

Storage—

To store this medicine:

• Keep out of the reach of children.
• Store away from heat and direct light.
• Do not store in the bathroom, near the kitchen sink, or in other damp places. Heat or moisture may cause the medicine to break down.
• Do not keep outdated medicine or medicine no longer needed. Be sure that any discarded medicine is out of the reach of children.

It is very important that your doctor check your progress at regular visits to make sure that the medicine is working properly and does not cause unwanted effects.

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

The following side effects may be caused by blood clots, which could lead to a heart attack or a stroke. Stop taking this medicine and get emergency help immediately if any of the following side effects occur:

• More common
  • Shortness of breath 
  
  

• Less common
  • Chest pain 
  
  

• Rare
  • Continuing or severe nervousness;  cough ;  dizziness or lightheadedness;  fainting;  fast heartbeat;  heart attack;  increased sweating;  nausea;  pain in chest, groin, or legs, especially the calves;  severe, sudden headache;  slurred speech;  severe and sudden, unexplained shortness of breath;  sudden loss of coordination ;  sudden, severe weakness or numbness in arm or leg ;  vision changes 
  
  

Also, check with your doctor as soon as possible if any of the following side effects occur:

• Less common
  • Bone fracture;  breast pain;  chills, fever, or flu-like symptoms;  mental depression;  swelling of feet or lower legs  
  
  

• Rare
  • Vaginal bleeding 
  
  

Other side effects may occur that usually do not need medical attention. These side effects may go away during treatment as your body adjusts to the medicine. However, check with your doctor if any of the following side effects continue or are bothersome:

• 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 and urination;  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;  unusual tiredness;  vomiting;  weakness;  weight gain 
  
  

Letrozole sometimes causes a loss of hair.

Other side effects not listed above may also occur in some patients. If you notice any other effects, check with your doctor.