As women enter menopause, their bodies produce very low levels of estrogen and progesterone. Normally, these hormones help cells communicate throughout the body and manage everything from digestion to immune function and libido. When hormone production begins to drop, people turn to medication and treatments to supplement their supply. Hormone replacement therapy works by providing the body with an extra boost of certain vital hormones such as estrogen, progesterone, and even testosterone. There are a variety of delivery methods including pills, patches, gels, vaginal creams, and vaginal creams.