hello, Premarin should be used for only as long as needed. The long-term use of estrogen hormones has been linked with increased risk of some cancers. Premarin also increases the risk of blood clots, heart attack, and stroke. You should keep seeing your doctor regularly to monitor your symptoms and to discuss how long to take Premarin.Hormone therapy after surgery -- either with estrogen and progestin or with estrogen alone -- is a way to counteract the supply of estrogen you ve lost. Women who have both the uterus and ovaries removed usually just get estrogen replacement therapy (ERT) alone. But women who have only the ovaries removed need both estrogen and progestin. That s because estrogen alone can increase the risk of cancer in the uterus. Adding progestin removes this risk.thank you