Used as a stable isotope-labeled internal standard in mass spectrometry and liquid chromatography-mass spectrometry (LC-MS) analyses for the accurate quantification of hexestrol and related estrogens in biological samples. Its deuterated structure allows differentiation from endogenous compounds, improving measurement precision in pharmacokinetic studies, doping control, and hormone metabolism research. Also employed in metabolic studies to trace the fate of hexestrol in biological systems without altering its chemical behavior.