Which Birth Control Pill Is Safest?
Researchers Find Differences in Blood Clot Risk in Different Oral Contraceptives
WebMD News Archive
Aug. 13, 2009 -- When it comes to the risk of blood clots, some oral
contraceptive pills are safer than others, according to new studies by European
"Oral contraceptives with levonorgestrel and a low dose of estrogen are
associated with the lowest risk of venous thrombosis [blood clots] and are
therefore the safest option," says Astrid van Hylckama Vlieg, PhD, a research
fellow at Leiden University Medical Center in the Netherlands, and the lead
author of one study.
''Our study shows that there is indeed a difference in the risk of venous
thrombosis associated with different types of progestins and different doses of
estrogens available in the contraceptive," she tells WebMD in an email
Similar results were obtained in the second study, evaluating Danish women.
Both studies are published in the online edition of BMJ.
Even with differences in risk, however, a U.S. expert who reviewed the
studies for WebMD points out that the differences are small and the overall
risk of getting a blood clot from the pill is very low to begin with.
The risk of blood clots associated with birth control pill use has been
known for decades, with several studies finding a twofold to sixfold increased
risk with the use of oral contraceptives. The new research confirms earlier
findings and adds new specifics about which hormones carry the most risk.
Birth Control Pills and Blood Clots
Van Hylckama Vlieg and colleagues compared 1,524 women, ages 18 to 50,
diagnosed with a first deep venous thrombosis (DVT) of the leg, which is a
blood clot in the leg, or a pulmonary embolism, a blood clot in the lung, and
compared them with 1,760 healthy people.
Women taking oral contraceptives had a fivefold increased risk of blood
clots compared with nonusers, and the risk differed by the type of progestin.
"The newer types of oral contraceptives containing drospirenone or cyproterone
acetate are associated with an increased risk compared with oral contraceptives
containing levonorgestrel," Van Hylckama Vlieg says. Specifically, the
researchers found that:
- Levonorgestrel boosted the risk of blood clots by nearly fourfold compared
- Gestodene boosted risk by 5.6 times.
- Drospirenone boosted risk 6.3 times.
- Cyproterone boosted risk 6.8 times.
- Desogestrel boosted risk 7.3 times.
The risk of blood clots was also associated with the level of estrogen in
the pills, with higher estrogen dose linked with higher risk.
In the national Danish study, researchers evaluated the risk of blood clots
among healthy Danish women, ages 15 to 49, who were using various types of
birth control pills from 1995 to 2005.
During that period, they observed 4,213 blood clots.
The risk decreased with duration of use and decreasing dose of estrogen.
Like the Dutch researchers, the Danish team found that pills with
levonorgestrel had a lower risk of blood clots than pills that contain other
types of progestins. They found pills with norethisterone to be lower risk,