Estetrol stable isotopes are a set of isotopes of the hormone estetrol that have a stable atomic structure and do not decay over time. These isotopes are used in medical research to study the effects of estetrol on the body and to develop new treatments for conditions such as osteoporosis, breast cancer, and menopausal symptoms. The stable isotopes allow for precise measurements and accurate analysis of estetrol metabolism in the body, providing valuable insights into its physiological functions.