Modern contraceptives may carry more risk

Women who take newer types of birth control pills face a higher risk of developing blood clots than women who take older types, researchers said this week, providing what some called “clarifying” evidence that more modern contraceptives designed as safer options may in fact pose more risk than earlier formulations.

University of Nottingham researcher Yama Vinogradova and colleagues examined two medical records databases to study more than 50,000 15- to 49-year-old women in Britain.

They found, as researchers have known for decades, that women who took combined oral contraceptives (formulations that include versions of two hormones, estrogen and progestin) had a higher risk of developing venous thromboembolisms — dangerous blood clots — than women who do not take the pill.

But when the team broke out the data by medication and controlled for other risk factors, they also discovered that certain versions of the birth control pill were associated with higher risk than others.

Medications using the synthetic hormones drospirenone (found in Yasmin), desogestrel (found in Kariva and Mircette) and other newer formulations were associated with about a 1.5 to 1.8 times higher risk than older drugs containing synthetic hormones such as levonorgestrel. The team’s study, published in the BMJ, confirms past findings, said Susan Jick, an epidemiologist at the Boston University School of Public Health who wrote an editorial accompanying the report.

“The results provide compelling evidence that these newer oral contraceptives are associated with a higher risk of venous thromboembolism than older options,” wrote Jick, who was not involved in the research but whose Boston Collaborative Drug Surveillance Program has conducted similar analyses.

Around the world, Vinogradova and her co-authors wrote, nearly 10 per cent of women of childbearing age use oral contraceptives, a number that grows to 18 per cent of women in developed countries. The risk of developing blood clots for such women, who are generally healthy, is low but real.

According to Jick, drug makers were attempting to create safer pills when they started using the newer synthetic hormones such as drospirenone.

“There were all these reasons one would think they should have been safer,” she said in an interview. “And yet they weren’t.”

Confirming the increased risk, however, has been difficult, Jick added, because different studies have been conducted in different ways — with some methodologies masking the medications’ effects.

“People should know that the risk is there,” Jick said.