Femara (letrozole) is an aromatase inhibitor used primarily in the treatment of hormone receptor–positive (HR+) breast cancer in postmenopausal adults. By lowering estrogen levels—an essential growth factor for many breast tumors—Femara helps slow or stop cancer cell proliferation. It is commonly prescribed for:
Off-label uses exist, most notably ovulation induction in certain infertility cases. Off-label use should only occur under the direct supervision of a qualified clinician who can weigh risks, benefits, and alternatives.
Estrogen fuels the growth of many HR+ breast cancers. Femara inhibits aromatase, the enzyme that converts androgens to estrogens in peripheral tissues. In postmenopausal individuals—whose ovaries no longer produce significant estrogen—this peripheral conversion is the dominant source of estrogen. By suppressing aromatase activity, Femara reduces circulating estrogen levels, depriving sensitive tumor cells of a key growth signal. This mechanism underpins its role in both early-stage and metastatic disease management.
Femara is not a chemotherapy agent and does not directly kill cancer cells. Instead, it creates an unfavorable hormonal environment for their growth. This targeted approach often results in a different side-effect profile than cytotoxic chemotherapy.
Femara is contraindicated in the following situations:
Discuss your medical history with your oncology team before starting therapy, especially if you have liver disease, osteoporosis or low bone density, high cholesterol, cardiovascular risk factors, or ongoing hormone replacement therapy (HRT).
Active ingredient: Letrozole. Femara is typically supplied as oral tablets intended for once-daily use. Generic letrozole may also be available and therapeutically equivalent when obtained through legitimate, licensed pharmacies.
Use Femara exactly as directed by your oncologist.
Your clinician will determine duration based on your diagnosis and response. In early-stage breast cancer, adjuvant therapy often lasts for multiple years. In advanced disease, treatment generally continues until disease progression or unacceptable toxicity. Do not start, stop, or change your dose without medical guidance.
Femara’s estrogen-lowering effect can influence multiple organ systems. Key considerations include:
Let your healthcare team review all medicines and supplements you take. Notable interactions include:
Do not start, stop, or change any medication without consulting your oncology team.
Many people tolerate Femara well, but side effects can occur. Common experiences include:
Strategies such as regular exercise, sleep hygiene, hydration, balanced diet, and nonhormonal symptom management can help. Always inform your care team about persistent or bothersome effects; adjustments and supportive therapies can substantially improve quality of life.
Seek urgent medical attention for any of the following:
This is not a complete list. Report any new or worsening symptoms to your oncology team promptly.
Your care team may recommend the following to ensure safety and effectiveness:
Keep all appointments and promptly complete lab work. Early detection of issues allows timely intervention and better long-term outcomes.
Femara is one of three commonly used aromatase inhibitors (the others are anastrozole and exemestane). While all reduce estrogen, subtle differences exist in side-effect profiles and patient tolerance. Compared with tamoxifen—a selective estrogen receptor modulator—aromatase inhibitors are often preferred for postmenopausal HR+ disease in many settings due to improved disease-free survival in certain trials. However, individual factors such as bone health, thrombotic risk, uterine history, tolerability, and personal preferences inform the optimal plan. Oncologists may recommend sequential strategies (e.g., tamoxifen followed by an aromatase inhibitor) to balance benefits and risks across years of adjuvant therapy.
Femara is available as branded and generic letrozole. Prices vary by region, formulation, pharmacy, and insurance. Many patients can access generic letrozole at reduced cost through insurance formularies, discount programs, or patient assistance initiatives. For safety and efficacy:
Call your healthcare provider or emergency services right away if you experience severe allergic reactions; chest pain or trouble breathing; sudden, severe headache; new neurological deficits; heavy or unexplained vaginal bleeding; signs of deep vein thrombosis; or symptoms of liver injury. Rapid evaluation can be lifesaving.
Commonly reported side effects include back, leg, or arm pain; breast discomfort; cough; diarrhea or constipation; dizziness; headache; hot flashes; flushing; increased sweating; indigestion; joint or muscle pain; reduced appetite; mild swelling or fluid retention; nausea; night sweats; insomnia; abdominal pain; fatigue; vaginal dryness or irritation; vomiting; subjective weakness; and weight changes. Most are manageable with supportive care—report persistent or worsening symptoms.
Serious adverse events can include severe allergic reactions; calf pain or tenderness; chest pain; confusion; fever or signs of infection; painful urination; numbness or weakness of one side; severe or persistent bone pain; severe abdominal pain; shortness of breath; sudden severe headache, vomiting, dizziness, or fainting; ankle or foot swelling; unexplained vaginal bleeding or discharge; and changes in vision or speech. Seek medical attention immediately for these symptoms.
In the United States, Femara (letrozole) is a prescription medication. Federal and state regulations require dispensing only pursuant to a valid prescription issued by a licensed clinician after an appropriate medical evaluation. For your safety and to comply with the law, do not attempt to obtain Femara from unverified sources or without medical supervision.
If you have questions about access or affordability, speak with your oncology team, a licensed pharmacist, or a social worker who can help you navigate safe, legal options that fit your clinical needs.
Femara is the brand name for letrozole, an aromatase inhibitor that lowers estrogen levels by blocking the enzyme aromatase. In postmenopausal women with hormone receptor–positive breast cancer, reducing estrogen helps slow or stop cancer growth.
Femara is prescribed mainly to postmenopausal women with estrogen receptor–positive (ER+) early or advanced breast cancer, either as initial therapy, after surgery as adjuvant therapy, or after several years of tamoxifen. It’s also used off-label for ovulation induction under specialist care.
For breast cancer, the standard dose is 2.5 mg taken once daily at the same time each day, with or without food. Swallow the tablet whole. If used for fertility, dosing and timing differ and must be directed by a fertility specialist.
Adjuvant therapy typically lasts 5 years, and some patients benefit from extended therapy up to 7–10 years depending on cancer risk, prior tamoxifen use, bone health, and side effects. Your oncologist will individualize duration.
Femara lowers the risk of cancer recurrence and can improve disease-free survival in hormone receptor–positive early breast cancer, especially in postmenopausal women at higher risk.
Hot flashes, joint and muscle pain, fatigue, headache, mild nausea, sweating, and sleep changes are common. Over time, bone thinning (osteopenia/osteoporosis) and increased cholesterol can occur, so monitoring is important.
Long-term estrogen suppression can reduce bone mineral density, raising fracture risk. Rarely, significant liver enzyme elevations or cardiovascular issues may occur. Severe persistent bone pain, chest pain, shortness of breath, yellowing of eyes/skin, or unexplained swelling warrants urgent evaluation.
Expect periodic assessments of bone mineral density (DEXA scans), vitamin D levels, lipid panel, and sometimes liver function tests. Your clinician will also review side effects, adherence, and recurrence risk at visits.
Acetaminophen and many NSAIDs can be used short term, but discuss frequent NSAID use due to stomach and kidney risks. Talk to your doctor before starting supplements; calcium and vitamin D are often recommended for bone health. Avoid products containing estrogen.
Yes. It can accelerate bone loss. Your care plan may include weight-bearing exercise, calcium (1,000–1,200 mg/day total intake), vitamin D (generally 800–2,000 IU/day, individualized), avoidance of smoking/excess alcohol, and possibly bone-protective medications (bisphosphonates or denosumab) if indicated.
Avoid estrogen-containing therapies (some hormone replacement therapies, certain vaginal estrogens without oncologist approval). Strong CYP3A4 inducers (like rifampin, carbamazepine, St. John’s wort) may reduce letrozole levels. There are no strict food restrictions.
Take it as soon as you remember the same day. If it’s nearly time for the next dose, skip the missed dose and return to your regular schedule. Do not double up.
In breast cancer, Femara is for postmenopausal women. In select cases, it may be combined with ovarian suppression in premenopausal patients under oncology supervision. For fertility, it is used off-label in premenopausal women under a reproductive specialist’s guidance.
Yes, off-label. Letrozole can induce ovulation and is commonly used for anovulatory infertility, including PCOS. Dosing and monitoring are different from cancer treatment and require a fertility specialist.
Some people report weight changes and hair thinning or shedding, though not everyone experiences these. Lifestyle measures and supportive care can help; discuss persistent changes with your clinician.
Moderate alcohol may be permissible for many, but alcohol can worsen hot flashes, dizziness, or fatigue and may affect liver health. If you have liver disease or struggle with side effects, limit or avoid alcohol and discuss with your doctor.
Femara is contraindicated in pregnancy because it can harm a developing fetus. Use effective non-hormonal contraception during treatment. For fertility use, it’s taken early in the cycle and cleared before conception; this must be supervised by a fertility specialist.
No. Breastfeeding is not recommended while taking letrozole, as it may pass into breast milk and affect the infant. Discuss feeding plans with your clinician.
Femara does not increase bleeding or clot risk like tamoxifen can, and it’s often continued through surgery. Always inform your surgeon and dentist; they will advise based on your overall health and procedure type.
Stop drinking, hydrate, rest, and avoid driving. If symptoms persist or are severe, contact your healthcare provider. Consider reducing or avoiding alcohol while on therapy.
Only with oncologist approval. Even low-dose local estrogen can affect systemic levels. Non-hormonal moisturizers and lubricants are preferred first-line.
Alcohol can further strain the liver. Avoid or strictly limit alcohol and coordinate care with your oncologist and hepatologist. You may need closer liver function monitoring.
Most cold medicines are safe, but alcohol combined with sedating antihistamines or cough suppressants can increase drowsiness. Avoid products with alcohol and check labels; ask your pharmacist if unsure.
After using Femara for cancer, discuss plans with your oncologist; timing depends on your cancer risk and treatment course. For fertility protocols, the medication is used early in the cycle and cleared before ovulation; follow your specialist’s timing exactly.
Yes. Femara is a brand name; letrozole is the generic. They contain the same active ingredient and are considered therapeutically equivalent.
Both are nonsteroidal aromatase inhibitors with similar effectiveness in postmenopausal ER+ breast cancer. Side effect profiles overlap (joint pain, hot flashes, bone loss). Individual tolerance may differ, so switching between them can help if side effects are problematic.
Exemestane is a steroidal aromatase inhibitor. Efficacy is comparable overall. Some patients tolerate one better than another; exemestane may have slightly different effects on lipids and hot flashes, while bone loss risk exists with all AIs.
Letrozole is often cited as producing the deepest suppression of circulating estrogen, though clinical outcomes across AIs are broadly similar. Choice is guided by side effect tolerance, prior therapy, and clinician preference.
They overlap greatly. Joint pain, stiffness, hot flashes, fatigue, and bone loss are common to all. Some patients report fewer joint symptoms on exemestane; others prefer letrozole or anastrozole. There is no universally “easier” option—individual response varies.
Yes. Letrozole (Femara) is 2.5 mg once daily, anastrozole (Arimidex) is 1 mg once daily, and exemestane (Aromasin) is 25 mg once daily, all typically taken at the same time each day.
All AIs can reduce bone mineral density. Comparative studies suggest similar fracture risks overall, though small differences may appear. Bone health monitoring and prophylaxis apply to all.
All can affect lipids; some data suggest exemestane may have a slightly different lipid profile, but results are mixed. Lipid monitoring and lifestyle or medication management are key regardless of AI choice.
Yes. Switching to anastrozole or exemestane is common when side effects persist. Many patients find improved tolerability after a switch without compromising cancer control.
Letrozole and anastrozole have few significant interactions; strong enzyme inducers can lower levels. Exemestane is metabolized by CYP3A4; strong inducers may reduce its exposure. Always review new medications with your oncology team.
All three are effective after tamoxifen. Some protocols use letrozole or anastrozole for sequential therapy, and others consider exemestane, particularly in switch strategies. The decision hinges on side effects, bone health, and recurrence risk.
All are available as generics (letrozole, anastrozole, exemestane), which are generally affordable. Brand-name versions cost more. Check your formulary and patient assistance programs.
Letrozole is the preferred aromatase inhibitor for ovulation induction; anastrozole is less commonly used. Exemestane is not typically used for fertility.
Efficacy is broadly comparable. Choice may depend on prior therapies, side effects, and whether combination therapy (e.g., with CDK4/6 inhibitors) is planned. Your oncologist will tailor the regimen to your situation.
Written on 2 March, 2023: Laura Jenkins
Re-written on 8 October, 2025: Cristina Matera, MD