The Associated Press reports:
"In briefing documents, the FDA says newer contra-ceptives have been less effective -- at times, with twice the failure rate -- than previous products, most likely because manufacturers have started using lower doses of hormones that stop ovulation."
Preventing ovulation is only one phase of hormonal birth control. Does this mean that the other two phases are being relied upon more? Evidence presented in previous discussions here on L&C would suggest so. The third phase is abortion due to thinned uterine lining preventing implantation. If ovulation is not prevented as successfully, more abortions must occur because the [reportedly lower] doses of hormones in today's formulations are still shown to thin the uterine lining enough to prevent implantation in most cases.
In addition, "Companies often exclude women who smoke, are overweight or have a history of heart problems from their trials." This leaves us to wonder how accurate even the studies are at overall performance of hormonal "contraception."