Letrozole (Femara)
LET-roh-zole
Category
Compound type
Phase / Status
FDA approved for breast cancer. Aromatase inhibition for other uses is typically off-label and should be clinically supervised.
Standard Dose
Daily (medical) or every other day (performance)
Half-life
Plasma elimination
Route(s)
Oral
Research Stage
Regulatory approval granted; post-market monitoring ongoing.
Overview
Letrozole decreases estrogen formation by inhibiting aromatase. It is used in approved cancer settings and must be prescribed because estrogen levels that are too low can affect bones, joints, mood, and cardiovascular risk in susceptible people.
Plain-language summary
Letrozole decreases estrogen formation by inhibiting aromatase. It is used in approved cancer settings and must be prescribed because estrogen levels that are too low can affect bones, joints, mood, and cardiovascular risk in susceptible people.
Administration Routes
- Oral
Also known as
Mechanisms
Non-steroidal competitive aromatase inhibitor (inhibits CYP19A1) to reduce conversion of androgens to estrogens. Effects depend on adherence and individual metabolism.
Detailed mechanism
Letrozole is a third-generation non-steroidal aromatase inhibitor that competitively and reversibly occupies the active site of CYP19A1 (aromatase) via its triazole nitrogen atoms coordinating with the heme iron, blocking the conversion of androstenedione and testosterone to estrone and estradiol respectively. This can reduce circulating estradiol by up to 98% in postmenopausal women and substantially lowers estrogen in men on exogenous androgen therapy, making it significantly more suppressive than anastrozole at comparable doses. The resultant estrogen deficiency alters negative feedback on the HPG axis, raising LH and FSH, which is exploited in fertility protocols to stimulate ovarian follicular development in women with anovulation.
Safety
Side effects
- Hot flashes and mood changes
- Joint pain/stiffness
- Potential bone density reduction with prolonged use
- Fatigue and possible cardiovascular/metabolic impacts depending on risk factors
Reported benefits
- Reduced serum estradiol in appropriate medical indications
- Aromatase inhibition can be beneficial in estrogen-dependent disease
- Long half-life supports once-daily regimens in many cases
Safety profile
Well-characterized safety profile in approved indications; adverse effects are monitored and managed clinically.
Clinical trials
Completed clinical trials supporting regulatory approval.
Structure
Verified structure
Letrozole (Femara)
Exact 2D structure can be rendered from a PubChem-backed canonical SMILES string.
- Chemical Formula
- C17H11N5
- Molecular Weight
- 285.30 g/mol
- CAS Number
- 112809-51-5
- InChIKey
- HPJKCIUCZWXJDR-UHFFFAOYSA-N
Stack Context
Stacks with
References
- 1View source
A randomized trial of letrozole in postmenopausal women after five years of tamoxifen therapy for early-stage breast cancer (MA.17 trial, NEJM)
2003
- 2View source
Adjuvant letrozole versus tamoxifen in postmenopausal women with hormone-receptor-positive breast cancer: initial results of the BIG 1-98 randomised trial (Lancet)
2005
- 3View source
Letrozole versus clomiphene for infertility in the polycystic ovary syndrome (NEJM)
2014
This profile summarizes research literature for education only. It is not medical advice, and it does not diagnose, treat, or recommend a dose. Consult a qualified professional before changing a protocol.