Newer contraceptive pill ‘ups clot risk’

WOMEN using newer versions of the contraceptive pill are at greater risk of developing potentially serious blood clots, according to two separate studies.

Researchers found a two-fold increased risk of a blood clot with pills containing drospirenone — a synthetic hormone — compared to the older levonorgestrel tablets.

A second comparison study using data from a general practice database in Britain, found a threefold increase of venous thromboembolism that can be fatal if the clots lodge in the lungs.

Researchers from Boston University School of Medicines said their findings provided further evidence that levonorgestrel oral contraceptives appeared to be a “safer choice”.

British scientists concluded that prescribing lower risk levonorgestrel oral contraceptives as the first-line choice would seem “prudent” in the absence of clear evidence that the drospirenone pill was more effective.

In the American study, blood clot rates were 31 for every 100,000 women years using the drospirenone pill and 12.5 per 100,000 women years using the levonorgestrel pill.

And in the British study, incident rates were 23 per 100,000 women years using the drospirenone pill and 9.1 per 100,000 women years using the levonorgestrel pill.

However, Dr Shirley McQuade, medical director of the Well Woman Centre, said the studies, published in the British Medical Journal, should be interpreted with caution and looked at in the context of previous studies.

She did not think there was sufficient evidence, based on the two small studies, to have women change their oral contraception.

Dr McQuade said all contraceptive pills increased the risk of a blood clot developing but, because the risk was so small, study numbers needed to be large to get the true picture.

She said neither of the studies accurately accounted for overweight/obesity, one of the risk factors for blood clots.

Dr McQuade said the authors of the study from 2009 that showed an increased risk in clotting with drospirenone have been asked to re-analyse the data because of possible flaws in the original work.

“There are several larger published studies that show there is no difference in risk between one type of pill and another,” said Dr McQuade.

She said the risk of getting a blood clot was greatest in the first three months of starting the pill and, after that, the risk was very low.