26 H 29 N O   Mol. mass 371.515 g/mol563.638 g/mol ( citrate salt) SMILES eMolecules & PubChem InChI InChI=1S/C26H29NO/c1-4-25(21-11-7-5-8-12-21)26(22-13-9-6-10-14-22)23-15-17-24(18-16-23)28-20-19-27(2)3/h5-18H,4,19-20H2,1-3H3/b26-25-   Key:NKANXQFJJICGDU-QPLCGJKRSA-N Tamoxifen is an antagonist of the estrogen receptor in breast tissue via its active metabolite, hydroxytamoxifen. In other tissues such as the endometrium , it behaves as an agonist