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Study says many women 'not on safest pill'

Second generation pills seem to provide most protection against venous thrombosis

OnMedica staff

Friday, 14 August 2009

While doctors stress that in general terms the risk of side-effects such as venous thrombosis are rare – some women are at a slightly raised risk because they are not taking the safest brand of the pill, according to new research.

Two separate studies in the British Medical Journal found that some oral contraceptives were linked with a higher risk of blood clot than others.

It has been accepted for many years that the combined pill, which contains both oestrogen and progestogen, is associated with an increased risk of venous thrombosis which can in some cases be serious and occasionally fatal, particularly if it breaks away and travels to the lungs.

The levels of oestrogen in the pill have been reduced over the years to help cut the risks.

However, this risk is far smaller than the risk of a clot during pregnancy.

A study by Dutch researchers from Leiden University Medical Centre - looking at data from 1,524 women who had developed venous thrombosis - found that overall taking the pill was associated with a five-fold increased risk of a clot. But within this group women taking pills containing a progestogen called levonorgestrel (for example, Microgynon) had the lowest risk of thrombosis at four times that of women not on the pill.

But those taking contraceptives containing desogestrel (for example, Mercilon or Marvelon) had the highest risk, at seven times that of those not taking the pill.

Women taking a pill with norgestimate (for example, Cilest) had an almost six-fold extra risk, as did those on drospirenone (for example, Yasmin).

Those taking a drug containing cyproterone acetate (for example, Dianette, which is often prescribed for acne) had an almost seven-fold additional risk.

"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," the researchers concluded.

The second study, by researchers from Copenhagen University in Denmark, also found that contraceptives containing levonorgestrel were associated with a lower risk than those containing desogestrel, gestodene or drospirenone.

Dr Nick Dunn, a GP and senior lecturer at the University of Southampton, said it was interesting that Yasmine, the newest type of pill, did not offer any advantage over more traditional ones.

But he added that those recommended by the researchers were probably the most commonly prescribed.

"What this says is we should stick to prescribing the well-trusted favourites but the chance of having a blood clot when on the pill are very low anyway."

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