Tamoxifen
Tamoxifen and its active metabolites (4-hydroxytamoxifen and endoxifen) competitively bind estrogen receptors (ER-alpha and ER-beta). The drug displays tissue-selective agonist/antagonist activity: it acts as an antagonist in breast tissue, blocking estrogen-driven tumor cell proliferation, while exhibiting partial agonist activity in bone (beneficial for bone mineral density) and endometrium (contributing to endometrial cancer risk with long-term use). In males, tamoxifen blocks estrogen receptor signaling in the hypothalamus and pituitary, increasing LH and FSH release and thereby stimulating endogenous testosterone production.
Injectable esters release over days to weeks depending on the ester; oral agents act within hours. Hormonal effects accrue over weeks, and dosing is individualized by a clinician.
Oral tablet; store at controlled room temperature (20-25 degrees C), protected from heat and moisture.
Clinical Evidence
What the literature says
Pharmacokinetics
- Routes
- Oral
Citations (3)
Last reviewed: 2026-06-15
Research Guide
How users approach this compound
The following reflects patterns observed in research literature and community protocols. This is not medical advice and does not constitute a clinical recommendation.
Reported Uses
- FDA-approved treatment of estrogen receptor-positive breast cancer (adjuvant, advanced, and DCIS settings)
- FDA-approved risk reduction in high-risk women
- Off-label: gynecomastia management in males (prescriber-directed)
- Off-label: post-cycle gonadotropin axis recovery in males (prescriber-directed)
Key Research Benefits
- FDA-approved for treatment and risk reduction of hormone receptor-positive breast cancer per label
- Studied off-label in males for management of gynecomastia and post-cycle restoration of gonadotropin axis (prescriber-directed)
Potential Side Effects
Considerations and Cautions
- Concurrent anticoagulant therapy with coumarin-type agents (increased VTE and bleeding risk)
- Personal or family history of venous thromboembolic events (relative contraindication)
- Pregnancy (embryotoxic potential)
- Concurrent use with aromatase inhibitors (pharmacodynamic interaction; reduced efficacy of each)
- Known hypersensitivity to tamoxifen
Labs to monitor
Educational context only, not a testing mandate. Any bloodwork decisions belong with your clinician.
- Estradiol (E2): Primary endpoint in off-label male use; SERM action at hypothalamus modulates estrogen feedback and E2 levels.
- LH and FSH: Confirms hypothalamic-pituitary axis response; primary endpoint for post-cycle use.
- Lipid panel: Tamoxifen has estrogen agonist activity in liver and may affect lipid metabolism; monitoring appropriate.
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Tamoxifen by goal
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Not medical advice
Information on DoseVault is for educational purposes only and is not a substitute for medical advice, diagnosis, or treatment from a qualified healthcare provider.