GlaxoSmithKline, which makes alli, says the pill will be available in U.S. stores by this summer.
Roche and GlaxoSmithKline are WebMD sponsors.
"This drug is only going to be effective if it's used in conjunction with a weight loss program -- and what that means is a reduced-fat diet, decreased calories, and an exercise program," said the FDA's Charles Ganley, MD, in a news conference.
"If someone just chooses to use orlistat alone -- without undertaking a weight loss program -- then this drug is not going to be very effective," says Ganley, who directs the FDA's Office of Nonprescription Products.
How Much Weight Loss?
"The labeling does state that for every 5 pounds you lose from diet alone, orlistat can help you lose 2-3 pounds more," Ganley says.
"In studies, most people lost 5-10 pounds over six months," he says.
"These studies were done in conjunction with a weight-loss program," Ganley notes.
People with a BMI (body mass index) of at least 27 may be the most likely to benefit from alli, Ganley notes.
"If you're markedly overweight -- where your BMI is over 30, for example -- you're likely to have more of a benefit than if it's a lower BMI," Ganley says.
The FDA doesn't recommend alli for people younger than 18, but it's not requiring buyers to show ID -- or otherwise restricting sales.
"We don't advocate that adolescents less than 18 use the product," Ganley says.
He says the FDA doesn't have "major safety concerns" about alli's use by younger adolescents.
"Our primary issue ... was that if adolescents have problems with weight, they should be followed by a health care provider," Ganley says.
"Although we understand that in some instances there may be adolescents that choose to use the product, that's not our intent. We certainly don't encourage it," Ganley says.
How Orlistat Works
Orlistat helps people lose weight by decreasing the amount of fat their intestines absorb.
The 60-milligram capsule can be taken up to three times per day and should be taken with meals that include fat.
Over-the-counter orlistat is not for people who have problems absorbing food or for those who are not overweight, states an FDA news release.
The labeling for alli notes the same side effects as prescription orlistat.
The product's most common side effect is a change in bowel habits, which may include loose stools. Eating a low-fat diet makes that side effect less likely, according to the FDA.
The FDA approved over-the-counter orlistat after reviewing GlaxoSmithKline's safety data and after submitting the product for consideration by an FDA advisory committee in January 2006. The committee voted in favor of over-the-counter approval.