What Is Letrozole? Uses, Dosage, and What You Need to Know in 2026

If you've been prescribed Letrozole — or are researching it for yourself or a loved one — you likely have a lot of questions. Is Letrozole chemotherapy? What exactly does it do? How long do you have to take it? This complete guide answers the most important questions about Letrozole in plain language.

What Is Letrozole?

Letrozole is a prescription oral medication that belongs to a class of drugs called nonsteroidal aromatase inhibitors (AIs). It works by blocking the enzyme aromatase, which converts androgens (male-type hormones) into estrogen. By blocking this enzyme, Letrozole dramatically reduces estrogen levels in the body.

The brand name of Letrozole is Femara, manufactured by Novartis. Generic Letrozole is available from multiple manufacturers and is bioequivalent to Femara.

Is Letrozole Chemotherapy?

No. Letrozole is not chemotherapy. It is a hormone therapy (also called endocrine therapy). Chemotherapy kills rapidly dividing cells throughout the body; Letrozole specifically targets the estrogen production pathway to deprive hormone-sensitive cancer cells of the estrogen they need to grow. Letrozole does not cause the classic side effects associated with chemotherapy (like severe hair loss, severe nausea, or immune suppression).

FDA-Approved Uses of Letrozole

Letrozole is FDA-approved for the following uses in postmenopausal women:

Adjuvant treatment of hormone receptor-positive early breast cancer: Taken after surgery, radiation, or other treatments to reduce the risk of breast cancer returning.

Extended adjuvant treatment after 5 years of tamoxifen: Continuing cancer protection for patients who have already completed a 5-year course of tamoxifen.

First-line treatment of locally advanced or metastatic breast cancer: For postmenopausal women with hormone receptor-positive or unknown receptor status advanced disease.

Second-line treatment of advanced breast cancer: For postmenopausal women whose breast cancer progressed during or after antiestrogen therapy (such as tamoxifen).

Off-Label Use: Letrozole for Fertility and PCOS

Letrozole is widely used off-label (meaning not in its FDA-approved indication) for ovulation induction in women with polycystic ovary syndrome (PCOS) and other ovulatory disorders. The American College of Obstetricians and Gynecologists (ACOG) and fertility guidelines now recognize Letrozole as the preferred first-line agent for ovulation induction in PCOS patients, surpassing the formerly dominant Clomid (clomiphene citrate). Studies have shown higher live birth rates with Letrozole compared to Clomid for PCOS patients (27.5% vs. 19.1% in a landmark NEJM study).

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Letrozole Dosage

Letrozole comes as a 2.5 mg oral tablet taken once daily. Dosing varies by use:

Breast cancer treatment: 2.5 mg once daily, typically for 5 years (some patients take it for 7-10 years depending on their cancer stage and risk profile). It can be taken with or without food.

Fertility/ovulation induction (off-label): 2.5-5 mg daily for 5 days per cycle, starting on cycle day 3 or day 5 of the menstrual cycle. Used cyclically until pregnancy occurs (typically up to 6 cycles).

How to Take Letrozole

Take Letrozole at the same time every day — choose a time that's easy to remember and stick to it

Can be taken with or without food — if nausea is a problem, try taking it with a meal

If you miss a dose, take it as soon as you remember — if it's almost time for your next dose, skip the missed dose

Never take two doses at once to make up for a missed dose

Continue taking Letrozole even if you feel well — stopping without your doctor's guidance can increase recurrence risk

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Who Should NOT Take Letrozole?

Pregnant women: Letrozole can cause serious fetal harm, including birth defects and miscarriage. Use effective contraception during treatment and for at least 3 weeks after the last dose.

Premenopausal women (for breast cancer use): Aromatase inhibitors are less effective before menopause because the ovaries continue producing estrogen. Letrozole should only be used in premenopausal women if they are also receiving ovarian suppression therapy.

People allergic to letrozole or any ingredient in the tablet

Is Letrozole a Controlled Substance?

No. Letrozole is not classified as a controlled substance by the DEA. This means it can be prescribed with standard prescriptions (no special forms required), transferred between pharmacies without restrictions, and prescribed via telehealth.

Want to understand more about how Letrozole works at the molecular level? See How Does Letrozole Work? Mechanism of Action Explained. If you need help finding Letrozole at a pharmacy, medfinder can help.