# Letrozole

*Also known as: Letro, Femara*

Potent non-steroidal AI; highest estrogen suppression of the three common AIs.

## Overview

Letrozole is a potent non-steroidal aromatase inhibitor developed for estrogen-receptor-positive breast cancer and used off-label to control estradiol during testosterone therapy or anabolic cycles. It competitively and reversibly inhibits the aromatase enzyme, and among the three common aromatase inhibitors it produces the deepest estradiol suppression, capable of reducing circulating estrogen by well over 90% at clinical doses. The compound has a roughly 33-hour half-life, near-complete oral bioavailability, and reaches steady estradiol suppression quickly, so very small infrequent doses can crash estradiol in self-directed use. The dominant and frequent risk is over-suppression, with severe joint pain, libido loss, lipid deterioration, dry membranes, and mood disturbance when estradiol runs too low. Harm reduction centers on conservative, symptom-driven dosing guided by estradiol bloodwork, never combining it with another aromatase inhibitor, and treating any new joint or libido symptom as a prompt to retest and back-titrate.

## Pharmacokinetics

- **Model tier:** advanced
- **Half-life:** 1.4 days (33.349999992 hours)
- **Cmax:** 45.684 ng/mL
- **Tmax:** 0.1 days
- **Bioavailability:** 99%

## Dosing

- **Default dose:** 1.25 mg
- **Typical range:** 0.625–2.5 mg
- **Units:** ng/mL

## Source

- **Label:** PubMed letrozole PK
- **URL:** https://pubmed.ncbi.nlm.nih.gov/16229115/

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**Canonical URL:** https://anabolicdex.com/compounds/letrozole
**Plot:** https://anabolicdex.com/plot?compound=letrozole