With one-third of the U.S. population overweight and another third obese, a lot of people out there are looking for a “magic pill” to make weight loss easier.

THE BIGGEST LOSER -- Episode 801 -- Pictured: (from left) Amanda, Rebecca, Sean, Shay, Rudolf, Charles, Alexandra, Julio, Antoine, Trracey, Mozziz -- NBC Photo: Dave Bjerke

It’s been 13 years since the Food and Drug Administration last approved a weight-loss drug, and that was Xenical, which has failed to win popularity because of side effects like diarrhea and flatulence.

On Wednesday the FDA gave the go-ahead to Arena Pharmaceuticals’ Belviq (generically known as lorcaserin) for prescription use in adults with a body mass index of 30 or greater (considered to be obese), or overweight adults with a BMI of 27 or higher who also have a weight-related medical condition such as type 2 diabetes, high blood pressure or elevated cholesterol levels.

If all you need to do is drop five pounds for swimsuit season, you’re out of luck.

But if you meet the FDA’s standards, you may be able to get a prescription once it’s available. Don’t expect dramatic results, however. In the three randomized, placebo-controlled trials of almost 8,000 overweight and obese people, study participants lost anywhere from 3 to at least 5 percent of their total body weight.

That’s three to five pounds per 100 that you weigh. In other words, a 200-pound man will lose six to 10 pounds. And that was over 52 to 104 weeks.

That may be enough in some cases. A major clinical study known as the Diabetes Prevention Program found that simply losing 5 to 7 percent of your body weight, along with 150 minutes of walking a week, reduced the risk of developing type 2 diabetes by 58 percent in overweight people with high blood sugar levels.

The new drug doesn’t work for everyone, though. The FDA-approved labeling states the medication should be discontinued in patients who don’t lose 5 percent of their body weight after 12 weeks of treatment.

Furthermore, people in the studies also received information on lifestyle modifications — like eating less and exercising more. Smaller portions and daily exercise are my “secrets” for a (so-far) 22-pound weight loss over the last 18 months.  

What Belviq may help with is controlling how much you eat. It activates a serotonin receptor in the brain that makes you feel full after eating less, so no more hunger pangs while trying to diet.

But any kind of medication, whether it’s an over-the-counter herbal supplement or an aspirin, carries risks. The FDA refused to approve Belviq in 2010 because of concern over the growth of tumors in rats and the possibility of heart valve problems in humans. Additional studies submitted this year apparently soothed the FDA’s fears, but Dr. Sidney Wolfe, director of the Public Citizen’s Health Research Group, isn’t convinced.

In a statement issued today, Wolfe wrote, “Marketing this drug to a population besieged by obesity and desperate for relief is irresponsible and a mistake that will benefit only the company that makes it.”

Remember fen-phen? That was the last “magic” weight loss pill, but the combination of fenfluramine and Phentermine damaged heart valves and caused primary pulmonary hypertension. It was pulled off the market in 1997, as was Meredia, another diet drug that caused high blood pressure and increased heart rate. Even the “natural” herb ephedra was banned by the FDA in 2004.

On the other hand, obesity can kill you. It increases your risk for type 2 diabetes, heart disease, high blood pressure, stroke and even certain cancers.

Weight problems are the number one reason Americans ages 17 to 24 are not medically able to serve in the military, according to Rep. Loretta Sanchez (D-Calif.), the ranking member on the House Armed Services subcommittee on strategic forces.

Obesity contributes as much as $168 billion a year to health care costs, estimates the Campaign to End Obesity.

It’s interesting that on the day before the U.S. Supreme Court upheld the Affordable Care Act, the FDA approved the first weight-loss pill in 13 years, addressing one of the country’s major health problems.

But it will take more than a pill twice a day to stem the rising tide of obesity. Policymakers, researchers and medical professionals need to work together to find solutions that will take the pounds off — and keep them off.

Diana Reese is a free-lance journalist in Kansas City and a contributing writer to "The Duke Encyclopedia of New Medicine." Follow her on Twitter at  @dianareese.