"Hormonal contraceptives have been used for decades and have an extremely safe track record," Campbell said. "So we feel good about the science that is out there. But this doesn't mean there shouldn't continue to be more research."
Dr. Cora Breuner of the American Academy of Pediatrics says her confidence in Plan B stems from the availability of long-term data about girls on the birth control pill.
"We know from repeated reviews there are girls on birth control and have been for years, and they have had no untoward effects," she says. "This isn't that different." The birth control pill and Plan B both contain the hormone progesterone, but Plan B includes it at higher levels.
Breuner also points out that the FDA approves a number of medications before having conducted studies that involve repeated observations of the same thing – such as a woman's fertility – over a long period of time.