Letrozole_Dosage, benefits & legal status
Also known as Femara, letrozol, LETRO
The stronger aromatase inhibitor, and the one with the clearest bone cost.
Common vial size is what vendors typically sell, not a recommendation. Enter your own vial in the calculator.
What is Letrozole?
Plain language first. The technical label stays, but it never stands alone.Overview
It shuts down estrogen production more completely than anastrozole does.
Letrozole is a non-steroidal aromatase inhibitor that competitively binds the heme group of the aromatase enzyme, cutting estrogen production across every tissue that makes it.
What it's used for
A breast cancer drug used on the research market when anastrozole is not holding estrogen down far enough.
How does Letrozole work?
What it does in the body, and where.Letrozole and anastrozole do the same job. Letrozole does more of it.
- 01It binds the heme group of aromataseThis is a competitive block on the enzyme that converts androgens into estrogen.
- 02Estrogen production falls across every tissueThe label notes it is highly specific, with no effect on adrenal steroid production, so cortisol and aldosterone are left alone.
- 03Bone pays for itThe bone substudy measured a median 4.1 percent fall in lumbar spine density at 24 months, against a small rise on tamoxifen.
- 04Nothing about this is gentleThe head-to-head trial data shows more fractures on letrozole and more clotting and endometrial events on tamoxifen. Each drug has its own cost.
A schematic of the compound's mechanism, not a diagnostic image.
What else is it used for?
Each use below carries its own evidence level. Approved means regulators have cleared it for that purpose. Investigational means it is in trials. Early research means it is being studied and is not established.
The published record
Papers and trials about Letrozole
364 papers tagged human · 228 not reviews or lab · 115 clinical trial publications
905 registered trials · 25 with posted results
Furthest stage reached: Approved in the US
Compare this against the whole library →
Prohibited at all times, in and out of competition. S4.1 Aromatase inhibitors (letrozole named). Specified Substance.RegulatorsCounted from Europe PMC indexing, not read by a person; a human tag can land on reviews, commentary or lab papers; clinical trial publications is the narrower count. 500 papers and 100 trials indexed in detail.
At a glance
Four things to know about Letrozole
Evidence
FDA-approved
Category
Sexual and hormonal
Common vial
Varies
Half-life
About 2 days
How much, and do you cycle it?
The range, and whether you take breaks.2.5 mg per day, daily. Continuous, for about five years in the trials FDA label
Median treatment duration in both the adjuvant and the extended adjuvant studies was five years, given daily throughout. The label states that the optimal duration is not known. There is no trial anywhere of the short intermittent courses used alongside a cycle.
About 2 daysFDA label
Terminal half-life of about 2 days, roughly 42 hours. Steady state is reached after 2 to 6 weeks of daily dosing.
Source: Femara label, Clinical Pharmacology
You can compare this against the whole library to see where it sits.
What does it cost?
Typical dose and cost, in plain numbers.Letrozole is not injected
It is taken by mouth (oral). One 2.5 mg tablet once a day, with or without food, in every approved indication. Splitting tablets to a fraction of this, which is common practice alongside testosterone, has no label and no trial behind it.
Letrozole starts at $109.99 across 3 vendors, typically $44.00 per mg.
3 listings, last read Oct 10, 2026. Shipping and card fees are not included.
How do you store it?
Before mixing, and after.Room temperature. Cool, dry, out of light.
Letrozole is taken as a pill or capsule. Keep it in its original container at room temperature, away from heat, humidity, and direct sun. No fridge or mixing needed. Check the expiration date on the bottle.
What are the side effects and cautions?
Known cautions and warnings for this compound.Who should avoid it
- Premenopausal hormonal status, which the label states outright
- Pregnancy, or any possibility of pregnancy
- Existing osteoporosis or low bone density, without a plan to manage it
- Known hypersensitivity to letrozole
- Banned in drug-tested sport
Stop and get help
- A bone fracture from a minor fall or knock
- Severe or sudden joint pain, or tendon pain, since tendonitis and rupture are reported
- Dizziness or drowsiness severe enough to affect driving
- Signs of an allergic reaction such as face or throat swelling, hives, or trouble breathing
Common effects
- Hot flushes
- Joint pain
- Fatigue and weakness
- Dizziness and drowsiness
- Raised cholesterol
- Falling bone density over months
Where this page says nothing is established, that means nobody has studied it, not that a compound is safe.
Is Letrozole approved?
And where the numbers on this page come from.Yes. Letrozole is FDA approved and available on prescription in the United States.
- Approval statusFDA-approved
- RouteBy mouth (oral)
- Checked24 August 2026
- DoseFrom the drug label. The manufacturer tested this range and a regulator reviewed it.
- Vial sizeFrom what vendors typically list; not a recommendation.
- Sources
What has happened recently
First approved in the US in 1997, for hormone receptor-positive breast cancer in postmenopausal women. The label contraindicates it in women of premenopausal hormonal status and states that clinical benefit in premenopausal women has not been demonstrated. There is no approved use in men. It carries warnings on bone mineral density and on total cholesterol, and product monographs also note tendonitis, tenosynovitis and rare tendon rupture across this drug class. Prohibited in sport at all times by WADA under section S4.
What regulators say
From official documentsProhibited at all times, in and out of competition. S4.1 Aromatase inhibitors (letrozole named). Specified Substance.
Checked 12 September 2026WADA: The 2026 Prohibited List (in force 1 January 2026)
Banned in drug-tested sport. Most research peptides are prohibited under WADA's S0 category, which covers any substance with no approval from any regulatory authority for human use. That means a compound can be banned without ever being named on the prohibited list. Check with your own anti-doping authority rather than assuming absence from the list means permitted.
You can compare this against the whole library, or read how to check a seller.
What else is like Letrozole?
Others in Sexual and hormonal, side by side.If you're weighing Letrozole, it's worth reading Cabergoline, Cetrorelix (Cetrotide), and Degarelix (Firmagon) in the same class.
The stronger aromatase inhibitor, and the one with the clearest bone cost.
- Dose
- 2.5 mg per day
- How often
- Daily
A prolactin drug whose label asks for an echocardiogram before the first dose.
- Dose
- 0.25 up to 1 mg per dose, twice a week
- How often
- Twice a week
A GnRH antagonist used in IVF to stop an egg being released too early.
- Dose
- Set by the label
- How often
- Daily during an IVF cycle
A GnRH antagonist for prostate cancer, and the one with no testosterone flare.
- Dose
- Set by the label
- How often
- Loading dose, then monthly
Guides for this compound
- mcg vs mg: The Peptide Dosing Mistake to Avoid
Your vial says mg and your protocol says mcg. Here is the conversion and how to check it.
Sources
- Femara prescribing information, DailyMed(2024)1997 initial US approval, premenopausal contraindication, bone and cholesterol warnings.
- Femara label PDF, FDA Drugs@FDA(2024)Bone substudy figures and the 96-month fracture comparison against tamoxifen.
Beyond these, 600 records are indexed. Browse the records