Pill or Patch?

The contraceptive patch has been gaining in popularity among women. But does it carry more risk of side effects than the Pill? In 2005 FDA issued a warning of a possible increased risk of thromboembolism in women using the patch because of higher average blood estrogen levels than those seen with the pill.

Using insurance claims data from UnitedHealthcare, scientists reported in the journal Obstetrics and Gynecology the results of a comparison of two form of the same hormone combination. Over 49,000 women took the norelgestromin/ethinyl estradiol patch (Ortho-Evra®), and over 200,000 used pills with the same hormones. The medical records showed that venous thromboembolism was more than twice as likely in patch users – 40 vs. 18 cases per 100,000 woman-years, in fact. Heart attack and stroke were too infrequent to allow an analysis of the relative safety of the two dosage forms.

Another study, just reported in the journal Circulation, demonstrates the opposite effect – oral, not transdermal estrogen increases the risk for venous thrombosis. Women who had a thrombosis were carefully matched with at least two control women (same age, center, time of year, etc). Users of oral estrogens, compared with non-users, were 4.2 as likely to develop thrombosis; estrogen patch users, however, were only 0.9 times as likely.

How to explain this? It’s probably due to the choice of progestogen rather than the route. But there were other differences between the two studies as well – e.g. examining the incidence among exposed women (first study) vs. case-control study (second). Once again, more research is needed. For instance, a study now running compares the effects of oral estrogen plus oral progesterone with that of patch estrogen and oral progesterone, looking at changes indicative of arterial disease and clotting factors. Studies like this will provide some answers. In the meantime, women taking the pill or the patch must not smoke, and should watch for possible early signs of venous thrombosis.