Study offers further evidence ‘the Pill’ linked to blood clots

Evidence continues to mount suggesting a link between a popular form of “the Pill” and a higher risk of blood clots.

New research involving nearly 330,000 women in Israel found that women taking birth-control pills containing the hormone drospirenone were as much as 65 per cent more likely to develop venous thromboembolism than women taking older generations of the pill.

Venous thromboembolism – or VTE – is a rare but potentially serious condition in which a blood clot forms in the deep veins of the legs or pelvis. Fragile clots can break away and travel through the bloodstream to the lungs, causing a pulmonary embolism – a medical emergency in which the clot becomes lodged in the lung.

There are two drospirenone-containing oral contraceptives on the Canadian market: Yaz and Yasmin. Their manufacturer, Bayer, is facing class-action lawsuits in Canada and the United States related to Yasmin, Yaz and generic versions of the drug.

Last year, there were 1.66 million prescriptions for Yasmin in Canada, worth more than $49 million. There were more than 619,000 prescriptions for Yaz, worth more than $21 million.

Combination birth control pills contain both estrogen and progestin. All contain the same estrogen component, but not the same progestin. Drospirenone is a unique progestin that’s promoted as causing less weight gain, acne and edema – water retention – than older-generation contraceptives containing different progestins.

Get weekly health news

Receive the latest medical news and health information delivered to you every Sunday.

Sign up for weekly health newsletter Get Started

By providing your email address, you have read and agree to Global News' Terms and Conditions and Privacy Policy.

The researchers in Israel looked at the blood-clot risk among women using different types of combined oral contraceptives.

They analyzed data on 329,995 women age 12 to 50 who received at least one prescription for the pills between 2002 and 2008.

During the study period, 359 cases of deep vein thrombosis and 159 cases of pulmonary embolism were newly diagnosed in the women.

The risk of blood clots was 65 per cent higher among drospirenone users than among women taking second-generation contraceptives containing levonorgestrel and norgestrel – derivatives of testosterone – and 43 per cent higher than women on third-generation pills, which contain desogestrel, gestodene and norgestimate.

The risk was highest in the first four months of use. High cholesterol, high blood pressure, cancer, obesity and older age were also found to be significant risk factors.

There was no difference in stroke risk among users of different pills.

The team found a “marked shift” away from the use of second-generation pills and an increase in the use of drospirenone-containing pills over the study period.

“With the increasing use of drospirenone-containing contraceptives, it is important to raise awareness of the increased, albeit small, risk of venous thromboembolism relative to third-generation pills, especially among those who are older or obese,” the researchers write in this week’s issue of the Canadian Medical Association Journal.

Lead author Dr. Naomi Gronich said that although there are no well-designed studies to show it, “There might be less side effects such as weight gain with drospirenone.

“Women want to take them. They have to know what the risks are, and their physicians should prescribe it more carefully, especially to higher-risk groups, ” said Gronich of Clalit Health Services Headquarters in Tel Aviv, the largest not-for-profit health-care provider in Israel.

The absolute difference in blood clots between different birth-control pills is small, and no regulatory or professional body has recommended against using drospirenone, Dr. Susan Solymoss, a hematologist at St. Mary’s Hospital and the Montreal General Hospital, wrote in a related commentary.

“The main thing is for women to ask for information, to (tell their doctor) if they’ve had any blood clotting in the family or if they’re concerned about blood clotting,” she said.

Two back-to-back studies published earlier this year in the British Medical Journal suggested that women taking drospirenone-containing pills might be two to three times more likely to develop blood clots than women taking pills containing levonorgestrel.

U.S. Food and Drug Administration advisers are scheduled to meet in December to review the safety of drospirenone-containing contraceptives. Health Canada is also reviewing the potential increased risk of blood clots with the pills.