For Research Use Only. Not for Use in Diagnostic Procedures.

4-Hydroxytamoxifen (4-HT) positive antagonist control for XenoScreen YES (Yeast Estrogen Screen) assay in antagonist mode. 4-HT is a potent selective estrogen receptor modulator (SERM) that competitively antagonizes estrogen receptor alpha (ERα) in the YES recombinant yeast strain.

In antagonist mode, the YES strain is co-exposed to a fixed concentration of E2 (agonist) and the test compound. A positive 4-HT response — reduced β-galactosidase activity versus E2-only control — confirms the assay correctly detects anti-estrogenic activity. 4-HT is the active metabolite of tamoxifen and is the reference ERα antagonist per OECD TG 457. Research use only.