Despite the label's warning that women of childbearing age should use birth control while on Qsymia, there are concerns that women will still get pregnant while on the drug. The FDA recommends a pregnancy test every month while on Qsymia.

In the drug-maker's two-year clinical trial, 34 women on Qsymia became pregnant, even though they were told repeatedly to use contraception. No birth defects happened in those pregnancies, according to the company.

Previous clinical trials of topiramate, one of the ingredients in Qsymia, have shown a risk of about five birth defects for every 1,000 pregnancies.

Comparing the anti-obesity drug to treatments for other chronic diseases, Troupin said patients will probably need to continue taking Qsymia long-term, though the new drug is not expected to be widely covered by health insurance plans.

Evans, the patient who lost 50 pounds on the drug, said she has gained back about 20 pounds since the clinical trial ended two years ago and looks forward to going on Qsymia once it's approved, even though it can have side effects.

"There are side effects to everything," she said.

She added that the drug wasn't the only reason she lost weight. Weekly counseling on nutrition and exercise were a big factor, too. The counselor helped her change her diet -- choosing a salad for lunch instead of a burger, forgoing pasta and potatoes at dinner -- and encouraged her to walk a few times a week in addition to her regular exercise as goalie in a women's soccer league.

"Before the medicine, I had been telling the girls they'd have to find a new goalie, because I couldn't dive for the ball like I did before," she said. "Then I lost the weight, and I was diving and bouncing back up and having a great old time again."