The clot and the pill

Women using latest versions of birth control pills stand a higher risk of developing blood clots

Last Updated: Saturday 04 July 2015

the contraceptive pill, discovered in the 1960s, has a success rate of 99.9 per cent and is one of the most popular contraceptives. It is said to have revolutionised women's lifestyles. But it is now known that the pill can cause problems such as weight gain, headaches, and disturbance in the levels of cholesterol. New versions of the pill can affect the development of blood clots in veins, known as venous thrombosis. Venous clots in the legs can become lethal if they migrate and block circulation to the lungs. Researchers from the Leiden University Hospital, Leiden, the Netherlands, have come out with an explanation for the relationship between the birth control pills and blood clots ( The Lancet , Vol 349, No 9059).

The first generation of pills introduced in the 1960s had high-dose, high-potency combination of the synthetic female hormones oestrogen and progestin. Pills with lower doses of hormones were introduced in the 1970s.These pills put the users at higher risks of heart attack, stroke, high blood pressure and breast cancer. The third generation progestin pills were introduced in 1992 with a combination of new synthetic substances that reduced the risks to the minimal for most of the users.

In 1995, the World Health Organisation ( who ) started working on the long established link between oral contraceptives and rare blood clotting problems. It was found that women taking the new generation birth control pills were twice as likely to develop venous thrombosis as those using the earlier versions. The condition was affecting an estimated 10 out of every 100,000 women taking the earlier generation pills, and over 21 of those taking the new low progestin pills.

Although the risk remained small, it was enough to prompt the Department of Health, uk , to issue a warning aboutthe risks, especially to those who were overweight, had varicose veins, or had a history of thrombosis. But the link between birth control pills and blood clots was not clear. The team at Leiden University claims to have established the link.

The Dutch team found that pills induce a resistance to the body's natural coagulation system. The blood coagulating system relies on a substance called activated protein c. Its functions have recently been understood. Tests conducted on the protein's anti-coagulating action in blood plasma showed that all women - regardless of what contraceptives they took - were less sensitive to the activated protein c than women who did not use any pills. And those with a genetic resistance to the activated protein c were 50 times more likely to develop thrombosis if they took the new generation pills.

The latest pills are less likely to cause the traditional side effects of the older pills like weight gain, headache, nausea, mid-cycle bleeding and disturbing the balance between 'good' and 'bad' cholesterol. But in the light of the recent studies as well as the who warning, doctors are more cautious about women's blood clotting problems before prescribing the pills.

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