Copenhagen: Taking contraceptive pills may be dangerous for the women, a research revealed.
The study said that some pills are more likely to cause serious blood clots.
One such clot is VTE or venous thromboembolism. This forms in the deep veins in one leg and may travel to the lungs, which can prove fatal in one out of three people.
Women on pills with one of the newer types of progestogen have double the risk of developing clots, say researchers led by Jvind Lidegaard from the University of Copenhagen.
Previous studies have indicated that the new types of progestogen hormone might increase the risk of VTE.
Lidegaard and colleagues carried out a large-scale study to assess its risk for women using oral contraceptives with different progestogens, according to a statement from the university.
They data came from Danish non-pregnant women aged between 15 and 49 years from January 2001 until December 2009, a science journal reports.
The participants had no previous record of either blood clots or cancer.
In absolute terms, the risk of VTE in current users of newer pills is about 10 per 10,000 women years.