Yasmin is the preferred choice among Irish women but it carries an almost six-fold added risk of blood clots, compared with women not on the pill.
Dutch researchers found that the safest option was an oral contraceptive containing levonorgestrel and combined with a low dose oestrogen, such as Microlite.
The research, published in the British Medical Journal (BMJ), is backed up by a Danish study, also published today, showing the thrombosis risk for levonorgestrel was lower than from other forms of progesterone.
A total of 1,524 women under the age of 50 who had suffered a thrombosis were followed for the Dutch study, led by experts at Leiden University Medical Centre in the Netherlands.
Dutch researchers found that women taking levonorgestrel had an almost four-fold increased risk of suffering venous thrombosis compared with women not on the pill.
Writing in the BMJ, the Dutch authors concluded: “Currently available oral contraceptives still have a major impact on thrombosis occurrence and many women do not use the safest brands with regard to risk of venous thrombosis.”
Medical director of the Dublin Well Woman Centre, Dr Shirley McQuade, said Yasmin, which contains a progesterone called drospirenone, was a big seller because it did not cause fluid retention. “Women who get bloating on other forms of progesterone prefer the contraceptive as it has a mild diuretic effect,” she explained.
She said the Well Woman worked from widely known studies suggesting the risk of blood clots increased from five in 100,000 women not on the pill up to 25 per 100,000 for those taking oral contraceptives.
Dr McQuade said pills containing levonorgestrel could affect a woman’s cholesterol level.
“If someone had no risk of heart disease in their family, no problems with their skin, then most doctors tend to go for the levonorgestrel-type one,” she pointed out.
“The older contraceptive pills that are safer in relation to blood clotting may not be as safe in relation to changing cholesterol levels,” she said.
“So, from a health point of view, there is not very much difference between them.”