Tibolone is a synthetic hormone used in hormone replacement therapy for postmenopausal women. Stable isotopes are non-radioactive isotopes of elements that have the same number of protons but different numbers of neutrons. Tibolone stable isotopes are used in research to study the metabolism and pharmacokinetics of the drug, as well as to develop analytical techniques for quantification of the drug in biological samples. These isotopes are also used in clinical studies to investigate the efficacy and safety of Tibolone in different patient populations.