There is no increase in risk of venous thromboembolism with third generation oral contraceptives, researchers say.
According to the results of an analysis of the General Practice Research Database, there has been no change in the incidence of venous thromboembolism despite a large fall in the use of third generation oral contraceptives. If the two were linked, a fall in both would be seen, say Professor R. Farmer and colleagues (pharmacoepidemiology and public health, postgraduate medical school, University of Surrey).
The study compared the use of third generation oral contraceptives, containing gestodene or desogestrel, and the rate of venous thromboembolism among women using oral contraceptives over two time periods.
The first, between January, 1993, and October, 1995, was before the Committee on Safety of Medicines announcement in October, 1995, that third generation pills were associated with twice the risk of venous thromboembolism compared with older oral contraceptives. This had resulted in a large number of women discontinuing use of such oral contraceptives. The second time period was after the announcement, between November, 1995, and December, 1998.
Data were taken from 304 general practices across the UK. The results show that overall use of combined oral contraceptives fell by 14 per cent in women aged 15-19 and 12 per cent in women aged 20-24. Out of all prescribed oral contraceptives, the proportion of third generation pills fell from 53 per cent to 14 per cent, say the authors. There was no change in the incidence of venous thromboembolism between the two periods. The incidence ratio adjusted for age was 1.04.
"If oral contraceptives containing gestodene or desogestrel had twice the risk of venous thromboembolism compared with older formulations, a reduction in their use would be expected to reduce the incidence of idiopathic venous thromboembolism. We found no such change," the researchers conclude (British Medical Journal 2000;321:477).