The consumer watchdog organization Public Citizen, in its Worst Pills Best Pills Newsletter for May, 2011, highlighted the February review in the French medical journal Prescrire International, of four studies examining the link between blood clots and oral contraceptives containing the progestin drospirenone.
Although two of the studies found no increase in the risk of blood clots in women taking the drug, both studies were funded by Bayer, the company that manufactures Yasmin and Yaz both of which contain drospirenone.
The two independent studies showed increases in the risk of blood clots in women taking drospirenone.
Previously, industry-funded studies also found lower risks than independently funded studies with respect to the increased risk of blood clots with other oral contraceptives containing desogestrel. Accordingly, one must consider whether the industry-funded studies were accurate or designed to yield the very result they achieved.
The large publicly-funded Danish study conducted between 1995 and 2005, and published in 2009, showed a statistically significant increase in the risk of blood clots in women taking drospirenone compared to those taking a combined contraceptive containing the older progestin levonorgestrel. It included all women in Denmark, ages 15 to 49, who did not have a previous history of heart disease or cancer and was the equivalent of 3.3 million women years, or the equivalent of 3.3 million women using an oral contraceptive for one year.
The second study, done in The Netherlands between March 1999 and September 2004 and also published in 2009, was made up of 1,524 women ages 18 to 50 years of age and 1,760 controls. The results were similar to those in the Danish study, and showed an increased risk of blood clots in women taking drospirenone compared to those taking levonorgestrel (3.6 vs. 6.3).
The following Tables were compiled by Public Citizen and contained in its May 2011 Newsletter, Worst Pills Best Bills.
TABLE 1: Estimated Risk of Blood Clots with Combined Oral Contraceptives Containing Different Progestins
Experts express risk as the number of incidents per person-year of exposure to a drug. In Table 1, contains estimates for blood clots in women using combined contraceptives containing ethinyl estradiol and various progestins including drospirenone, desogestrel and levonorgestrel or norethisterone. As the table shows, the risk is clearly lower with combined contraceptives containing levonorgestrel or norethisterone.