Short answer: Letrozole has a half-life of about 2 days. People vary, so treat these as estimates.
Letrozole is a nonsteroidal aromatase inhibitor: it blocks aromatase, the enzyme that converts androgens such as testosterone into estrogens. It is sold as Femara and as generic tablets.
Also known as: Femara.
Femara and generic letrozole come as 2.5 mg tablets, the only strength on the FDA label.
The FDA Femara label approves letrozole only for postmenopausal women with breast cancer: adjuvant treatment of hormone receptor-positive early breast cancer, extended adjuvant treatment after 5 years of tamoxifen, and first- or second-line treatment of advanced breast cancer. The labeled dose is 2.5 mg once a day, with or without food; in people with cirrhosis and severe liver impairment the label dose is 2.5 mg every other day.
The label says letrozole can cause fetal harm and is contraindicated in pregnancy, and that animal studies suggest it may impair fertility in both females and males. In a 24-month study in women after breast cancer surgery, median lumbar spine bone density fell 4.1% on letrozole versus a 0.3% rise on tamoxifen.
Other uses are off-label. In fertility care, a 2014 trial in 750 women with polycystic ovary syndrome (Legro, NEJM) found more live births with letrozole than with clomiphene (27.5% vs 19.1%). In men on TRT, the American Urological Association 2018 guideline says clinicians may use aromatase inhibitors, hCG or SERMs in men with testosterone deficiency who want to maintain fertility (a conditional recommendation), and notes that only hCG is FDA approved for use in males. Whether to take it, and how much, is a decision for you and your prescriber. See also anastrozole and exemestane.
The FDA Femara label gives a terminal elimination half-life of about 2 days. Steady state after daily 2.5 mg dosing is reached in 2 to 6 weeks, at levels 1.5 to 2 times higher than a single dose predicts. The label says letrozole is rapidly and completely absorbed but gives no time to peak, so we do not list one.
Numbers shown are taken from the source above. Half-life varies from person to person.
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