An article published in 2009 in the British Medical Journal by Dr. A. van Hylckama Vlieg (et al.) analyzes the risk of developing a blood clot for women using hormonal contraceptives (versus non-users) and evaluates the relative risk for developing a blood clot between different types of hormonal contraceptives used today, naming the active chemical in the drug commonly known as YAZ® as significantly more dangerous than the average hormonal contraceptive.
For this study, Vlieg surveyed 1524 women who had developed blood clots regarding their use of hormonal contraceptives, and found that 72.4% were using such contraceptives at the time of the clot. And through statistical analysis, the study establishes that “overall, current oral contraceptive use was associated with a fivefold increased risk of venous thrombosis” (Venous thrombosis is the instance of a blood clot.)
Among different oral contraceptives, however, health risks are not equal. Evaluating the rate of venous thrombosis among users of many oral contraceptives commonly used today, Vlieg found that users of contraceptives containing drospirenone (such as YAZ®) are placed at a 70% greater risk of venous thrombosis than the average oral contraceptive user, and 630% more likely to develop a blood clot than is a non-user.
A lawyer can use this article in a Yaz lawsuit to demonstrate that drugs such as YAZ® pose an unnecessarily high risk of venous thrombosis to users, considering that there is no observed increase in drug efficacy to theoretically justify the risk.
 Vlieg, A.H., et al. (2009) “The venous thrombotic risk of oral contraceptives, effects of oestrogen dose and progesterone type: results of the MEGA case-control study” BMJ2009;339;b2921; p. 3
 Vlieg, A.H., et al. (2009) “The venous thrombotic risk of oral contraceptives, effects of oestrogen dose and progesterone type: results of the MEGA case-control study” BMJ2009;339;b2921; p. 4