"If you're taking this product because you're looking for convenience, that's actually going in the wrong direction," said Amy Allina, program director of the National Women's Health Network, in an interview with ABC's "World News."
She said that while this pill might lead women to think there is something wrong with having a period, women on Lybrel would often experience bleeding when they're not expecting it.
Miller feels Lybrel is safe but has raised several questions about Lybrel's approval.
While nearly 80 percent of women were no longer "bleeding," Miller pointed out that less than 60 percent of the women involved had their menstrual blood flow stop completely. The difference was that some of the women experienced "spotting" — slight bleeding, which occurred irregularly, although it was slight enough that the women did not require a pad or tampon.
"If the goal is 'not blood,' they still need to improve it," she said. "The problem is that it doesn't necessarily deliver no periods for all women who take it."
Miller also pointed to the fact that 19 women became pregnant while on Lybrel, with only four of those failures attributed to mistakes by the users, and the rest attributed to "method." She speculated that this might have delayed Lybrel's approval.
Lybrel's failures, Miller said, might be due to the fact that it is a reduced dose of treatments than were used in the past. That, coupled with the increased average weight of the American woman, could lead to the drug's occasional ineffectiveness.
To combat that issue, Miller said, birth control pills should focus less on branding and more on adjusting doses to allow adjustments for weight.
"Not every dose is going to fit every woman," Miller said.
Simply making adjustments to the levels of progestin and estrogen in doses would be ideal for women, said Miller, who questions why Wyeth can't market a drug that simply adjusted those levels.
"I'm really surprised they got a patent," she said.
Miller also questioned the dropout rate in the study. Of the 2,134 subjects who began the study, more than half did not complete it — a rate Miller said is unusually high.
Wyeth did not respond to calls seeking comment.
Miller said that one potential problem may arise from women who carry excess iron in their blood, a condition known as hemochromatosis. Without menstrual bleeding, she said, females might develop it at a higher rate.
But despite her reservations, Miller still believes that women stand to benefit from Lybrel's introduction, since studies have shown that not having a period isn't inherently unsafe.
"It's nice that the conversation is happening," she said. "It's nice for the world to recognize you don't need a fake period."
ABC News medical correspondent Brian Hartman and Dr. Supinda Bunyavanich contributed to this report.