(HealthDay News) — Among oral hormone therapy users, conjugated equine estrogens (CEE) use is associated with a higher risk of incident venous thrombosis and possibly myocardial infarction than estradiol use, according to a study published online Sept. 30 in JAMA Internal Medicine.

Nicholas L. Smith, Ph.D., from the University of Washington in Seattle, and colleagues compared cardiovascular event risk associated with current CEE and estradiol use among 384 postmenopausal female members (aged 30 to 79 years using oral hormone therapy) of a large health maintenance organization in which the preferred formulary estrogen changed from CEE to estradiol during the study period.

The researchers found that among participants who were all current users of oral CEE or estradiol there were 68 venous thrombosis, 67 myocardial infarction, and 48 ischemic stroke cases. Current oral CEE use compared with current oral estradiol use was associated with an increased venous thrombosis risk (odds ratio [OR], 2.08) and an increased, though not statistically significant, risk of myocardial infarction (OR, 1.87). There was no association with ischemic stroke risk (OR, 1.13). CEE users compared with estradiol users among the 140 controls had higher endogenous thrombin potential-based normalized activated protein C sensitivity ratios, indicating a stronger clotting propensity.

“These findings need replication and suggest that various oral estrogen drugs may be associated with different levels of cardiovascular risk,” the authors write.

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