New weight-loss shot: How well does it work?

A new injectable drug, aimed at helping obese and seriously overweight people who have other weight-related health conditions, has proven effective in a new round of testing.

The drug, called liraglutide (brand name Saxenda), won FDA approval for use as a weight loss treatment in December, but with a requirement for further testing. The latest study involved 3,700 people from six continents and showed similar results to those in the previous trial: improved weight loss and control of blood sugars, but also several known side effects. The findings are published in this week's New England Journal of Medicine.

"The overall effect of the drug was very good and very comparable or better than the drugs that are now on the market," lead researcher Dr. Xavier Pi-Sunyer of Columbia University Medical Center told CBS News.

"This is a new generation of drug," CBS News medical contributor Dr. Holly Phillips explained on "CBS This Morning." "It's actually been around for a couple of years to treat diabetes but was just approved by the FDA for weight loss in December. So this study really aimed to make sure that it was effective for weight loss."

Study participants were given a reduced-calorie diet and an increased exercise regimen, along with either Saxenda or a placebo. Those who took Saxenda lost an average of 18 and a half pounds over 56 weeks. Those taking a placebo only lost 6 pounds.

That's three times as many pounds lost, but Phillips notes, "In the grand scheme of things, we have to think this is a pretty mild or moderate weight loss, when you compare it to something like gastric bypass or lap-banding, the surgical interventions."

Sixty-three percent of those who received the shot lost more than 5 percent of their body weight, versus 27 percent who used a placebo. And 33 percent lost more than 10 percent of their body weight with Saxenda, versus only 10 percent with the placebo. Users also experienced health benefits such as lower cholesterol, lower blood sugar, and better diabetes control.

The drug "tends to decrease gastric emptying, the emptying of the stomach. And it gives signals to the brain to lower hunger and increase satiety," said Pi-Sunyer.

The drug is given as a daily shot under the skin. Its approval was limited to adults who are obese or who are overweight and have at least one related condition, such as high blood pressure, type 2 diabetes or high cholesterol.

This weight-loss drug is not for casual use. The most common side effects included nausea, diarrhea, constipation, vomiting, low blood sugar and loss of appetite. Other rare but serious side effects include pancreas inflammation, gallbladder disease, lowered kidney function, suicidal thoughts, increased heart rate, and possible increased risk of thyroid cancer.

The study was funded by the drug's manufacturer, Novo Nordisk, which was required by the FDA to conduct further safety testing and to keep a 15-year history of cases showing serious side effects.

This is the fourth weight-loss drug approved by the FDA since 2012.