Letrozole
Femara · Aromatase inhibitor
What it is
A potent breast-cancer aromatase inhibitor that also circulates in AAS contexts for estrogen suppression.
What human evidence shows
Oncology-grade evidence for estrogen suppression — near-complete at prescription doses. In men and in non-medical contexts there is no controlled evidence base, and excessive estrogen suppression is a real, documented state.
Risks
Excessively suppressed estrogen is its own syndrome — low libido, joint pain, mood deterioration, lipid damage, and bone-density loss with time; recovery varies. In men, chronic low estrogen is a documented path to osteoporosis.
Legal status
US: prescription-only. Products outside licensed dispensing are unapproved and of uncertain concentration.
Evidence base
established literature
Large human evidence base: several phase 3 or 4 trial reports, plus multiple meta-analyses or systematic reviews.
- phase 3/4
- 170
- randomised
- 574
- reviews
- 175
- human trials
- 810
Counts are of published papers, not distinct trials, and measure how much research exists — not whether this works or is safe for you.
Research (12)
- Palbociclib and Letrozole in Advanced Breast CancerN Engl J Med · 2016
- Letrozole: Pharmacology, toxicity and potential therapeutic effectsLife Sci · 2022
- Letrozole for Female InfertilityFront Endocrinol (Lausanne) · 2021
- LetrozoleExpert Opin Drug Metab Toxicol · 2010
- Aromatase inhibitors (letrozole) for ovulation induction in infertile women with polycystic ovary syndromeCochrane Database Syst Rev · 2022
- Palbociclib plus letrozole as first-line therapy in estrogen receptor-positive/human epidermal growth factor receptor 2-negative advanced breast cancer with extended follow-upBreast Cancer Res Treat · 2019
- Letrozole and Unexplained Infertility: A Contemporary Meta-analysisJ Obstet Gynaecol Can · 2019
- Effects of letrozole combined with clomiphene in the treatment of polycystic ovary syndrome: a meta-analysisBMC Womens Health · 2025
- Comparing efficacy and safety of stair step protocols for clomiphene citrate and letrozole in ovulation induction for women with polycystic ovary syndrome (PCOS): a randomized controlled clinical trialJ Med Life · 2023
- Efficacy of letrozole for the treatment of tubal ectopic pregnancy: A meta-analysisEur J Obstet Gynecol Reprod Biol · 2024
- Letrozole pretreatment prior to medical termination of pregnancy: a systematic reviewContraception · 2018
- Letrozole for Ovulation Induction in Women With Polycystic Ovary SyndromeObstet Gynecol Surv · 2026
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