This medication is used to treat certain types of breast cancer (such as hormone-receptor-positive breast cancer) in women after menopause. Letrozole is also used to help prevent the cancer from returning. Some breast cancers are made to grow faster by a natural hormone called estrogen. Letrozole decreases the amount of estrogen the body makes and helps to slow or reverse the growth of these breast cancers.

This section contains uses of this drug that are not listed in the approved professional labeling for the drug but that may be prescribed by your health care professional. Use this drug for a condition that is listed in this section only if it has been so prescribed by your health care professional.

This drug may also be used for infertility in women.

Read the Patient Information Leaflet if available from your pharmacist before you start using letrozole and each time you get a refill. If you have any questions, ask your doctor or pharmacist.

Take this medication by mouth with or without food as directed by your doctor, usually once daily.

Dosage is based on your medical condition and response to treatment.

Use this medication regularly to get the most benefit from it. To help you remember, take it at the same time each day.

Since this drug can be absorbed through the skin and lungs, women who are pregnant should not handle this medication or breathe the dust from the tablets. (See also Precautions section.)

Tell your doctor right away if your condition gets worse (such as you get new breast lumps).

Hot flashes, hair loss, bone pain, tiredness, unusual sweating, nausea, diarrhea, dizziness, and trouble sleeping may occur. If any of these effects last or get worse, tell your doctor or pharmacist promptly.

Remember that this medication has been prescribed because your doctor has judged that the benefit to you is greater than the risk of side effects. Many people using this medication do not have serious side effects.

Tell your doctor right away if you have any serious side effects, including:

• nausea/vomiting that doesn't stop
• bone fractures
• pain/swelling of the joint/muscle/tendon
• mental/mood changes (such as depression, anxiety)
• swelling of arms/legs
• blurred vision
• unusual tiredness
• dark urine
• yellowing eyes/skin.

This medication (and cancer) may rarely cause serious problems from blood clots (such as heart attack, stroke, blood clots in the lungs or legs). Get medical help right away if you experience:

• shortness of breath/rapid breathing
• chest/jaw/left arm pain
• confusion
• sudden dizziness/fainting
• pain/swelling/warmth in the groin/calf
• trouble speaking
• weakness on one side of the body
• sudden vision changes
• sudden/severe headaches
• unusual sweating

A very serious allergic reaction to this drug is rare. However, get medical help right away if you notice any symptoms of a serious allergic reaction, including:

• rash
• itching/swelling (especially of the face/tongue/throat/neck)
• severe dizziness
• trouble breathing

This is not a complete list of possible side effects. If you notice other effects not listed above, contact your doctor or pharmacist.

In the US - Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088 or at www.fda.gov/medwatch.

In Canada - Call your doctor for medical advice about side effects. You may report side effects to Health Canada at 1-866-234-2345.

Before taking letrozole, tell your doctor or pharmacist if you are allergic to it; or to anastrozole; or if you have any other allergies. This product may contain inactive ingredients, which can cause allergic reactions or other problems. Talk to your pharmacist for more details.

Before using this medication, tell your doctor or pharmacist your medical history, especially of:

• high blood fats (cholesterol)
• bone problems (such as osteopenia, osteoporosis)
• stroke or blood clots
• heart disease (such as chest pain, heart attack, heart failure)
• high blood pressure
• kidney problems
• liver problems

This drug may make you dizzy or tired or rarely blur your vision. Alcohol or marijuana (cannabis) can make you more dizzy or tired. Do not drive, use machinery, or do anything that needs alertness or clear vision until you can do it safely. Limit alcoholic beverages. Talk to your doctor if you are using marijuana (cannabis).

Before having surgery, tell your doctor or dentist about all the products you use (including prescription drugs, nonprescription drugs, and herbal products).

This medication must not be used during pregnancy. It may harm an unborn baby. Letrozole is used mainly in women after menopause. If you have recently gone through menopause, discuss the need for use of reliable forms of birth control while taking this medication and for 3 weeks after stopping treatment with your doctor. Do not use birth control products containing estrogen. Consult your doctor for more details. If you become pregnant or think you may be pregnant, tell your doctor right away. (See also How to Use section.)

It is unknown if this drug passes into breast milk. Because of the possible risk to the infant, breastfeeding is not recommended while using this drug and for at least 3 weeks after the last dose. Consult your doctor before breastfeeding.

Drug interactions may change how your medications work or increase your risk for serious side effects. This document does not contain all possible drug interactions. Keep a list of all the products you use (including prescription/nonprescription drugs and herbal products) and share it with your doctor and pharmacist. Do not start, stop, or change the dosage of any medicines without your doctor's approval.

Some products that may interact with this drug include:

• estrogens (such as ethinyl estradiol, conjugated estrogens)
• estrogen blockers (such as anastrozole, tamoxifen)
• tibolone

If someone has overdosed and has serious symptoms such as passing out or trouble breathing, call 911. Otherwise, call a poison control center right away. US residents can call 1-800-222-1222. Canada residents can call 1-844-764-7669.

Do not share this medication with others.

Lab and/or medical tests (such as bone density tests, cholesterol levels, liver function) should be done while you are taking this medication. Keep all medical and lab appointments. Consult your doctor for more details.

This medication can increase the risk of bone loss (osteoporosis). Talk with your doctor about your risk, and about available treatments for osteoporosis. Lifestyle changes that reduce the risk of bone loss include doing weight-bearing exercise, getting enough calcium and vitamin D, stopping smoking, and limiting alcohol.

If you miss a dose, take it as soon as you remember. If it is near the time of the next dose, skip the missed dose. Take your next dose at the regular time. Do not double the dose to catch up.

Store at room temperature away from light and moisture. Do not store in the bathroom. Keep all medications away from children and pets.

Do not flush medications down the toilet or pour them into a drain unless instructed to do so. Properly discard this product when it is expired or no longer needed. Consult your pharmacist or local waste disposal company.