conjugated estrogens Premarin A brand of conjugated estrogens used in menopausal hormone therapy today. Premarin was utilized in transgender hormone therapy by Harry Benjamin for the first time in 1948. Premarin was derived from Emmenin in order to lower manufacturing costs and so was derived from the urine of pregnant mares instead (hence the name Premarin, from pregnant mares' urine). PREMARIN PREMARIN®