In the 10 weeks since the new antiobesity drug Saxenda came on the market, Elias S. Siraj has prescribed it for "a few patients."

It's too soon for Siraj, who directs the diabetes program at Temple University Hospital , to judge whether the Novo Nordisk medication will overcome diet drugs' history of being barely effective, unsafe, or both. As the headline of his editorial in the current New England Journal of Medicine says: "Another Agent for Obesity - Will This Time Be Different?"

"We have a huge obesity problem in this country. But it's a very expensive medication, and an injection," said Siraj, who coauthored the editorial with endocrinologist Kevin J. Williams. "My expectation is that the patients who will benefit the most are those who have" weight-related health problems.

Saxenda (generic name liraglutide), a daily injection approved by the Food and Drug Administration late last year, is the fourth weight-loss drug approved since 2012. But while the three others - Belviq, Qsymia, and Contrave - work largely by tinkering with brain chemicals, Saxenda is part of a new class of diabetes medicines that prompts the pancreas to make extra insulin after meals.

Novo Nordisk first got approval to sell it five years ago as a diabetes therapy called Victoza. The new, higher-dose version is specifically for weight loss in obese patients (a Body Mass Index of 30 or more), and in overweight adults (BMI of 27 or more) who have at least one weight-related problem such as high blood pressure, high cholesterol, or diabetes. (Like all prescription obesity drugs, it is supposed to be combined with diet changes and exercise.)

While Saxenda fights obesity in a novel way, it does not make pounds melt away, any more than other drugs. Indeed, the FDA considers a drug effective if it enables a 5 percent weight loss, because that is enough to promote health improvements such as lower blood pressure.

In a pivotal study published with his editorial in the journal - one of the studies the FDA relied on - 64 percent of patients taking Saxenda for a year lost at least 5 percent of their weight, and 33 percent lost at least 10 percent. In the placebo group, 27 percent of patients had a 5 percent weight loss, and 10 percent had a 10 percent loss.

Relatively small losses, Siraj said, "may not look great. You may not even see it. But it does lead to metabolic improvements. It can relieve" weight-related health problems.

Saxenda patients also had a benefit that Siraj called "remarkable": Their rate of newly diagnosed diabetes was less than one-eighth of the rate in the placebo group. Novo Nordisk is now researching this finding.

Major obstacles to obesity drugs are cost and insurance coverage.

Saxenda costs $1,068 a month. Coverage varies, said Clare Krusing, a spokeswoman for America's Health Insurance Plans, a trade group representing most of the nation's payers.

Some plans explicitly exclude prescription weight-loss drugs. Some provide coverage, but with restrictions and time limits.

For example, Independence Blue Cross, the leading plan in Southeastern Pennsylvania, said it generally does not cover weight-loss drugs. If such prescriptions are allowed, prior approval would be required to determine the medical necessity.

Keeping weight off without drug therapy is another challenge, Siraj noted. Patients in the study who were randomly assigned to stop taking Saxenda after 56 weeks regained an average of 6.4 pounds - about a third of the 18.5 pounds they had lost.

Saxenda's main side effects were nausea and diarrhea that went away within days. A trial is underway to evaluate long-term cardiovascular effects, as well as breast cancer and thyroid cancer risks.

The importance of watching for long-term dangers was demonstrated by fenfluramine and dexfenfluramine, two wildly popular diet drugs that were yanked in 1997 after evidence that a third of users could develop heart-valve damage.

"Given previous disappointments with various weight-loss strategies, these are welcome findings," Siraj concluded of Saxenda. "Still, liraglutide is no cure."