Description
Letrozole (Femara) is a non-steroidal, reversible third-generation aromatase inhibitor. Like Anastrozole, Letrozole is a triazole derivative but has stronger binding affinity at the aromatase enzyme and lowers estradiol levels by 88-98% - significantly stronger than Anastrozole.
Per study reports this high potency is both advantage and disadvantage. Advantage: with strongly aromatizing compounds (e.g., high-dose test combined with Dianabol) or in acute gynecomastia research findings, Letrozole brings estradiol levels down quickly and safely. Disadvantage: fine adjustment is difficult. Crash levels (E2 under 10 pg/ml) easily occur.
In the anabolic research literature Letrozole is often used as a “reverse gyno” tool: 2.5mg/day for 14 days can reverse established gynecomastia symptoms in research setups, at a speed not achievable with Tamoxifen or Anastrozole.
The strong E2 lowering has documented side effects: in longer use joint pain, bone density loss, unfavorable lipid profile. Clinically Letrozole is often combined in breast cancer therapy with calcium and vitamin D supplements to mitigate bone effects.
Pharmacokinetically orally bioavailable with about 42-hour half-life. Steady-state is established after 4-6 weeks - practically meaning acute effect extends beyond daily doses.
You can order Letrozole as oral tablets with 2.5mg per tablet, as a blister of 10, a pack of 30 or a bottle of 100 tablets.
This information is for research and educational purposes only. No medical recommendations.
Risks & Safety
Letrozole sits in the mid range of the risk scale. As the strongest non-steroidal aromatase inhibitor its high potency is both advantage and risk - the danger lies in the very easily occurring estradiol crash.
Documented in studies and the literature:
- Estradiol crash: crash levels with E2 below about 10-15 pg/ml easily occur under Letrozole because the E2 lowering reaches 88-98% - clinically problematic.
- Joint pain: with too-deep estradiol, joint pain is documented in longer use.
- Bone density: sustained low estradiol is associated with bone density loss. Clinically, Letrozole is often accompanied by calcium and vitamin D supplements.
- Lipid profile: an unfavorable lipid profile under strong E2 lowering is described in the literature.
- Difficult fine adjustment: the high potency makes precise dosing hard, so estradiol monitoring is closely recommended in the literature.
Monitoring via bloodwork is recommended. This classification does not replace medical advice. Risk and responsibility for any actual use lie entirely with the buyer.
Studies
- Superior Efficacy of Letrozole Versus Tamoxifen as First-Line Therapy for Postmenopausal Women With Advanced Breast Cancer - Journal of Clinical Oncology 2001, Mouridsen et al: First-line approval study on Letrozole.
- A Comparison of Letrozole and Tamoxifen in Postmenopausal Women with Early Breast Cancer - New England Journal of Medicine 2005, Thürlimann et al: BIG 1-98 - large randomized long-term RCT with an extensive safety dataset.
- Differences between the non-steroidal aromatase inhibitors anastrozole and letrozole - of clinical importance? - British Journal of Cancer 2011, Geisler: Review of the pharmacology comparison of the aromatase suppression of Letrozole and Anastrozole.
- Letrozole normalizes serum testosterone in severely obese men with hypogonadotropic hypogonadism - Diabetes, Obesity and Metabolism 2005, De Boer et al: Letrozole effect on the male gonadal axis in obese hypogonadism.
- Letrozole once a week normalizes serum testosterone in obesity-related male hypogonadism - European Journal of Endocrinology 2008, Loves et al: Dose and dosing-interval study on Letrozole in men, including supraphysiologic excursions.
