The relative risks of thrombotic stroke and myocardial infarction (MI) are higher among users of hormonal contraception, although absolute risks remain low, a Danish study conducted at Copenhagen University  showed.

Use of oral contraceptives combining low-to-moderate doses of ethinyl estradiol and various progestins was associated with up to 2.3 times the risks of thrombotic stroke or MI compared with non-use.The type of progestin in the pill had little effect on the risks, the researchers reported in the June 14 issue of the New England Journal of Medicine.

To put the risk in perspective, they estimated that among 10,000 women taking a pill combining desogestrel with ethinyl estradiol at a dose of 20 μg for 1 year, two will have arterial thrombosis and seven will have venous thrombosis.

"Although venous thrombosis is three to four times as frequent as arterial thrombosis among young women, the latter is associated with higher mortality and more serious consequences for the survivors," they wrote. "Therefore, these figures should be taken into account when prescribing hormonal contraception."

Several previous studies have examined the relationship between hormonal contraceptive use and the risk of venous thromboembolism. But fewer have looked at arterial complications like thrombotic stroke and MI, and the results have been mixed.

In an accompanying editorial, Diana Petitti, MD, MPH, of Arizona State University in Tempe, said that the absolute increases in the risks of thrombotic stroke and MI observed in the study were small."None of the hormonal contraceptives studied ... were associated with an excess risk of stroke that was unacceptable, considering their contraceptive and noncontraceptive benefits," she wrote.

And, she added, evidence from previous studies "shows that the small risk could be minimized and perhaps eliminated by abstinence from smoking and by checking blood pressure, with avoidance of hormonal contraceptive use if blood pressure is raised."

The researchers acknowledged the study was limited by possible diagnostic misclassification, the potential for a time lag between the date of prescription and when the contraceptives were started, the lack of information on body mass index, and the incomplete information on smoking status.

Source reference:
Lidegaard Ø, et al "Thrombotic stroke and myocardial infarction with hormonal contraception" N Engl J Med 2012; 366: 2257-2566.