Our physicians know that when prescribing estrogen, progesterone needs to be included as well in most cases. Progesterone’s job is to make sure the uterus stays lean and healthy. If you have a uterus, it's important to take progesterone alongside estrogen, to mitigate the risk for an overgrowth of uterine cells which can lead to cancer. If you no longer have a uterus, it is generally considered safe to take estrogen alone.