Two studies published in the current issue of the British Medical Journal have found that some oral contraceptives are linked with a higher risk of blood clot than others and that many women may not be taking the safest brand of the oral pill.

The combined pill, which contains both oestrogen and progestogen, has long been associated with an increased risk of venous thrombosis — a blood clot that forms in a vein. The studies found that the risk of venous thrombosis in current users of combined oral contraceptives decreases with duration of use and decreasing oestrogen dose. The levels of oestrogen in the pill have been reduced over the years to help cut the risks.

In the first study done by Dutch researchers — looking at data from 1,524 women who developed venous thrombosis — they found that taking the pill was associated with a five-fold increased risk of a clot. But closer analysis showed that women taking pills containing a progestogen called levonorgestrel had the lowest risk of thrombosis at four times that of women not on the pill. Whereas those on contraceptives containing desogestrel had the highest risk, at seven times that of those not taking the pill. Women taking a pill with norgestimate had a six-fold extra risk as did those on drospirenone. Those taking a drug containing cyproterone acetate had an almost seven-fold additional risk.

The second study, by Danish researchers, also found that contraceptives containing levonorgestrel — like I-pill in India — were associated with a lower risk than those containing desogestrel, gestodene or drospirenone.

... contd.