What Women Need to Know About Blood Clots

Newer birth control pills and blood clot risk linked


Taking "the pill" has become a routine part of life for many women around the world. But that doesn't mean birth control pills are entirely without risk.

A new study found that women who used newer types of birth control pills had a higher risk of blood clots.

"About 9 percent of women of reproductive age worldwide use [birth control pills]," wrote lead study author Yana Vinogradova, research fellow in medical statistics at the University of Nottingham, UK, and colleagues. "This percentage rises to 18 percent of women in developed countries and 28 percent of women in the United Kingdom. Although [birth control pills] are generally effective in preventing pregnancy, they have measurable side effects such as venous thromboembolism (VTE)."

VTE involves a blood clot in a deep vein — often in the leg — which can sometimes result in a clot that moves to the lungs. VTE can cause serious complications and death.

Blood clots form when there is damage to the lining of a blood vessel. These clots often occur in the legs or the pelvic veins, and symptoms may include swelling, warmth, redness or pain.

Vinogradova and team looked at risk of VTE among women who used both newer and older forms of birth control pills. These pills differed in the types of hormones used.

The pill is considered a type of hormonal contraception. Birth control pills contain small amounts of man-made estrogen and progestin hormones, which work to inhibit the body's natural hormone cycles to prevent pregnancy. Research on the effects of other hormonal contraceptives, such as the patch or the vaginal ring, was not included in this study.

Vinogradova and team looked at more than 10,562 women in the UK between the ages of 15 and 49 who experienced a first-time VTE between 2001 and 2013. They compared these women to more than 40,000 women of similar ages who did not experience VTE.

These researchers found that women using older birth control pills — like those containing the hormones norethisterone (brand name Micronor) and norgestimate (Ortho Tri-Cyclen) — had about a 2.5 times increased risk of VTE compared to women who did not use any oral contraceptives.

Newer pills — like those containing the hormones desogestrel (Mircette) and drospirenone (Yasmin) — were found to increase the risk of VTE about 3.6 to 4.3 times.

"Combined, the results provide compelling evidence that these newer [birth control pills] are associated with a higher risk of [VTE] than older options, despite attempts to develop safer hormonal contraceptives for women," wrote Susan S. Jick, DSc, of the Boston University School of Public Health, in an editorial about this study.

In an interview with dailyRx News, Steve Leuck, PharmD, pharmacist and founder of AudibleRx, said that while these findings are alarming, they are not necessarily surprising.

"Hormonal contraceptive therapy is already labeled with a Black Box Warning which is the most significant warning a medication may receive," Dr. Leuck said. "This particular warning states specifically, 'Smoking cigarettes while taking this medication significantly increases your risk of stroke, heart attack, blood clots and high blood pressure. This risk significantly increases if you are over the age of 35 years old.'"

In a press release, these researchers said that birth control pills are still considered safe and that pregnant women have a higher risk of VTE than the birth-control related risks seen here.

"[Women] should not stop using them, but should consult their doctor and review their current type of pill at their next appointment if there are any concerns,” Vinogradova said.

Dr. Leuck also stressed the importance of conversations between patients and health care providers about medications.

"Understanding the warnings associated with hormonal contraceptive therapy, what to look for with regards to potential side effects, and what to do about missed doses is critical if patients are to obtain the best possible outcome of therapy while avoiding adverse events," Dr. Leuck said.

This study was published May 26 in the journal The BMJ.

One study author disclosed ties to ClinRisk, a software company that works with clinical risk algorithms. No funding sources were disclosed.