Estrogen-associated hypercoagulability: Hyper-coagulable blood (a supranormal tendency for blood to clot) occurs as an occasional but serious side effect of estrogen therapy. The blood clots in this situation are dose-related; that is, they occur more frequently with higher doses of estrogen. All estrogen therapy preparations carry this risk. Cigarette smokers on estrogen therapy are at a higher risk for blood clots than nonsmokers. Therefore, patients requiring estrogen therapy are strongly encouraged not to smoke.