Which Pill is Best?

Birth control hormones safety reviewed in a recent report

/ Author:  / Reviewed by: Joseph V. Madia, MD Beth Bolt, RPh

(RxWiki News) Birth control pills are some of the most common medications prescribed in the United States. Therefore, it is important to know about the different risks that different pills have.

A recent report looked at several studies to provide a more thorough examination of birth control medications and their link to dangerous blood clots.

The authors of this report concluded that women taking combination birth control pills were more likely to develop blood clots than women not taking them.

All combination birth control pills contain two hormones, an estrogen (ethinyl estradiol) and a progestin. The report also showed that higher doses of estrogen compounds have been linked to blood clotting, and different types of progestin compounds increased women's risk of blood clotting.

"Talk to your gynecologist about the risks of birth control pills."

Bernardine Stegeman, a research associate with the Department of Epidemiology and Public Health of University College London, and several colleagues conducted this review in order to provide information about oral contraception and its risks.

Combined oral contraception, or combination birth control pills, has been linked to an increased risk of venous thrombosis, a blood clot inside of a vein.

Venous thrombosis can sometimes break off and travel to the lungs to create a pulmonary embolism. A pulmonary embolism occurs when a blood clot blocks one of the lungs' main arteries. It can be a life-threatening condition.

Birth control pills are made up of hormone compounds, usually of estrogens and progestins. Lower doses of the estrogen compound have been associated with a lower risk of venous thrombosis.

New types of progestin compounds have been developed, with different types belonging to different classes, or "generations," of progestin. 

Because there are so many options for oral contraception with different risks for venous thrombosis, the researchers reviewed existing studies to look at the risk for venous thrombosis among women based on which generation of progestin they used.

The researchers used observational studies that examined healthy women taking combination oral contraceptives who developed venous thrombosis. They found 25 publications written about 26 different studies in which at least 10 women in the study had died from venous thrombosis while taking combination oral contraceptives.

The two studies that reported the risk for venous thrombosis in women who did not take birth control pills showed that those women had a risk of 1.9 and 3.7 cases per 10,000 woman-years, or years of childbearing, for developing blood clots. Fifteen other studies showed that, for women taking combination birth control pills, that risk quadrupled.

A total of 23 studies were used to assess the risks associated with each generation of progestin compounds.

Among first generation progestin users, the risk for venous thrombosis increased 3.2-fold compared with women who did not take birth control pills.

Second generation progestins came with a 2.8-fold increased risk, and third generation projestins had a 3.8-fold increased risk of developing venous thrombosis.

The highest risk for venous thrombosis was associated with pills that included 50 μg ethinylestradiol with levonorgestrel. The lowest risk was associated with 20 μg ethinylestradiol with levonorgestrel and 20 μg ethinylestradiol with gestodene.

This report was published in BMJ on September 12.

Two of the authors were supported by research grants, and no other conflicts of interest were disclosed. The report received no specific funding.

Review Date: 
September 13, 2013
Last Updated:
September 18, 2013