Myocardial infarction risk and hormone replacement: Differences between products

ObjectivesTo establish the risk of myocardial infarction (MI) in users of hormone replacement therapy (HRT) compared with non-users and to compare the risk between different HRT regimens.MethodsA population-based cohort and case-control study, and a case-control study nested within a cohort of HRT users, using the UK General Practice Research Database. Differences between HRT regimen, mode of administration and duration and recency of use were examined whilst adjusting for confounding.ResultsIn the cohort and case-control study, 4537 cases of MI were identified in 2.62 million observed women years, cases were age-matched to 27,220 controls. In both studies, current and past HRT use were associated with reduced risk estimates for MI compared with no prior use. MIs were less likely to be fatal amongst women who had used HRT than amongst never users (ORadj 0.58; 95% CI 0.45–0.75). No difference in risk was seen between current and past use, oral and transdermal HRT or between different regimens (p > 0.44). In the nested study, no difference was found in the association with MI risk between different oestrogen–progestogen combinations or between different combinations and tibolone. Unopposed oestrogen use was not associated with a decrease in risk compared with combined HRT.ConclusionsThese results are consistent with previous observational studies in supporting the hypothesis that use of postmenopausal HRT is associated with a decrease in risk of acute myocardial infarction (AMI). Case fatality differed between HRT users and non-users, suggesting a protective effect of HRT. This study does not demonstrate a difference between regimens.