New contraceptive pills carry twice risk of blood clots

Published on Thursday 13 August 2009 22:09

WOMEN taking newer contraceptive pills are twice as likely to get potentially-fatal blood clots than those using the older varieties, according to a new study.

Researchers say many women are not using the safer older brands and should consider switching to reduce the danger of suffering a deep vein thrombosis (DVT).

They found women on the pill have an overall fivefold increased risk of a DVT compared with non-users. The clots can be fatal if they move inside the circulatory system and lodge in the lungs.

But the risk differed according to the type of hormone they contained. Third generation pills containing desogestrel were associated with a twofold increased risk of DVT over the second generation pills with the hormone levonorgestrel.

The risk was also linked with a higher dose of oestrogen and was most prevalent among women using the pill for the first time, irrespective of the type of contraceptive used.

Epidemiologist Professor Frits Rosendaal, of the Leiden University Medical Centre in the Netherlands, and colleagues said the best option for women was an oral contraceptive containing levonorgestrel combined with a low dose of oestrogen.

Prof Rosendaal, whose findings are published in the British Medical Journal, said although the overall risks were small, they should be considered when deciding which oral contraceptive to use.

All current brands are "equally effective at preventing pregnancy", so the choice should be based on "the smallest increase of side effects".

Prof Rosendaal said: "It is estimated that 100 million women use an oral contraceptive worldwide. With such a large number of women using oral contraceptives, even the smallest increase of side effects will affect many.

"Knowledge of these risks and efforts to reduce them are of crucial importance. Our results clearly show that the safest option with regard to the risk of venous thrombosis is an oral contraceptive containing levonorgestrel combined with a low dose of oestrogen."

A second study also found that blood clot risk from the pill decreased with duration of use and reduced oestrogen dose.