Many studies suggest estrogens and progresterones can increase blood clotting.
The magnitude of risk, however, is debatable. Studies showing no difference in risk may only indicate a poor study design or that the study was not large enough. All users of these medications are wise to consider clotting a potential risk. Being aware of symptoms such as swelling, redness, or pain is important. Users of these drugs should know that clots can travel to the lungs and can be fatal.