Sulfates are the major circulating conjugates of ethinyl estradiol and glucuronides predominate in urine. The first oxidative metabolite is 2-hydroxy ethinyl estradiol, shaped by the CYP3A4 isoform of cytochrome P450. A part of the primary-pass metabolism of ethinyl estradiol is thought to come about in gastrointestinal mucosa. Ethinyl estradiol ma