Combined oral contraceptives have been known as a well-established contraceptive method already more than 50 years. Unfortunately, this method is not absolutely safe. Combined oral contraceptives include estrogens and progestagens, which may stimulate the blood coagulation and promote the occurrence of deep-vein thrombosis; adverse effects of oral contraceptives are also notably associated with increased risk of stroke and myocardial infarction. The risk of hypercoagulation and venous thrombosis is most likely to be influenced by the dose of estrogens, but recent investigations have showed that the type of progestagens is very important as well.