[Wulf Utian], a consultant in gynecology to the Cleveland Clinic, prefers prescribing cyclical hormones for HRT patients because he feels this form better mimics the body's hormone cycle before menopause. "There's no model in nature where an animal or human is continuously exposed to estrogen and progesterone," he said, explaining that, before menopause, the body releases estrogen during the first half of the hormonal cycle and progesterone during the second half.
When oral medications that contain hormones are swallowed, they often have a hard time making it past the liver, which has a tendency to absorb and excrete hormones rather than allow them to enter the bloodstream, said Fred Abramson, a professor of pharmacology at George Washington University Medical Center. The hormones in patches and the vaginal ring avoid the liver problem and are absorbed directly into the bloodstream. Thus, their bioavailability appears to be higher. And in fact, said Abramson, hormones administered vaginally have in some cases had a bioavailability 40 times that of oral hormones.
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