What is a primary risk factor for developing thromboembolic disease when taking oral contraceptives?

Smoking is a primary risk factor for developing thromboembolic disease in individuals using oral contraceptives due to the synergistic effects of nicotine and estrogen on the vascular system. Estrogen can increase the risk of blood coagulation, and when combined with smoking, the risk of thrombosis is significantly heightened. Smoking leads to endothelial damage and increases the levels of certain clotting factors, which can predispose a person to the formation of clots.

While factors such as age, family history, and noncompliance with dosing can influence thromboembolic risk, they do not interact with estrogen in the same direct and potent way as smoking does. For example, although being over 30 may pose some increased risk, it is smoking that produces a notable amplifying effect on the risks associated with oral contraceptive use. Family history can be significant, but it represents a hereditary risk rather than an acute and modifiable risk factor like smoking. Noncompliance with dosing could lead to irregular hormone levels, but it does not specifically enhance the risk of thromboembolic disease to the same extent as smoking combined with the estrogen in oral contraceptives.