Tamoxifen Citrate
Triphenylethylene SERM; tissue-selective estrogen antagonist/agonist
Mechanism of Action
Tamoxifen is a selective estrogen receptor modulator (SERM) of the triphenylethylene class. It functions as a competitive antagonist at estrogen receptors (ER) in breast tissue, inhibiting estradiol-mediated proliferation. Paradoxically, it acts as a partial agonist in bone and endometrial tissue, maintaining bone density while posing endometrial proliferation risk. Tamoxifen is metabolized by CYP2D6 and CYP3A4 to active metabolites including endoxifen and 4-hydroxytamoxifen, which have 30-100x greater ER binding affinity than the parent compound. In research contexts, tamoxifen is studied for estrogen-mediated gynecomastia prevention and HPTA recovery.
Evidence Level
Clinical Trial - Human
6 studies published
Pharmacology
Molecular Weight
371.5 g/mol (free base); 563.6 g/mol (citrate salt)
Half-Life
5-7 days (parent); 9-14 days (active metabolites)
Bioavailability
Approximately 100% oral bioavailability