A study released Monday contributes to the growing pile of evidence that suggests newer types of birth control pills carry increased risks of blood clotting and may not be safe for certain groups of women.

The study looked at 330,000 Israeli women and found a strong likelihood that those who used birth control pills with the hormone drospirenone, which is used in brand-names like Yaz and Yasmin, were more likely than other Pill users to develop blood clots called venous thromboembolisms.

Although the numbers are relatively small, only six per 10,000 users, the risks were 43 percent higher with drospirenone-containing pills, compared with older, second- and third-generation pills, which becomes more than 10 per 10,000 or 0.1%, which is relatively high.

Dr. Susan Solymoss of McGill University in Montreal, who wrote an editorial published with the study in the Canadian Medical Association Journal, reminded readers that:

“It’s important to remember that all oral contraceptives are associated
with a risk of blood clots.”

She went on to clarify that women don’t really need to panic or quit their contraceptives, simply have a discussion with their doctor and think into their circumstances, lifestyle and medical and family history.

Dr. Naomi Gronich, who led the new study, agreed with Solymoss.She said that age is another factor. Gronich, of the Technion-Israel Institute of Technology in Haifa told Reuters Health that blood clot risk gradually increased after the age of 25. Obviously not taking birth control pills is an option for any woman. However, as Solymoss pointed out, other contraceptives may not be as effective at preventing pregnancy.

“And pregnancy is a bigger risk for
blood clots.”

Its always good to put things into perspective with some hard numbers as statistics can be misleading. For every 10,000 women who become pregnant in a year, about 20 will develop venous blood clots. That compares with the rate of six women per 10,000 among Pill users overall and three in 10,000 women who are not on the pill.

Bayer HealthCare, the manufacturer of Yaz, Yasmin, Beyaz and Safyral, said it was still reviewing the new study from Israel and could not comment on it. Bayer also looked to its own post-marketing studies that have failed to turn up a heightened clot risk with drospirenone contraceptives versus older ones. Drospirenone is a progestin, a synthetic version of the hormone progesterone.

The different “generations” of the Pill have slightly varying types of progestin. Second-generation pills contain the progestins levonorgestrel or norgestrel. These tended to cause side effects like acne and body-hair growth more frequently. With this in mind, the third-generation of progestins were developed in the 1980s to lower the risks of those problems. Some studies found that third-generation pills carried a higher blood clot risk than their predecessors, suggesting that risk is influenced by the progestins in the formulation.

Yaz was approved in 2006 and quickly became the top-selling birth control pill in the U.S. though its sales have dropped off in the past couple years (partly because of generic competitors). Worldwide, Yaz and its sister pills had sales of about $1.07 billion in the first nine months of this year, according to company financial statements. The “Yaz” products have been promoted as causing less weight gain and swelling than older-generation pills. Yaz and Beyaz can also be used to manage moderate acne or so-called premenstrual dysphoric disorder, a severe form of PMS that causes physical symptoms and serious mood swings before a woman’s period.

For women who have already been using Yaz or related pills without noticeable problems, there may be no reason to switch, according to both Solymoss and Gronich. In this study, Gronich pointed out, blood clot risk was greatest in the first few months of use :

“A woman already on drospirenone for four months probably shouldn’t be more worried than if she (were on) another second- or third-generation contraceptive.”

Written by Rupert Shepherd