Mestranol-d4 is the deuterium labeled Mestranol. Mestranol is an inactive proagent and becomes biologically active on conversion to ethinyl estradiol (EE). Mestranol acts as an estrogen receptor agonist. Mestranol combines with a progestin in vivo and can be used for the research of menopausal hormone or menstrual disorders. Mestranol-d4 is a click chemistry reagent, it contains an Alkyne group and can undergo copper-catalyzed azide-alkyne cycloaddition (CuAAc) with molecules containing Azide groups.