The Danish group, the world's biggest insulin producer, said on Monday it was pleased with the results. But investors worried about where it left Novo's strategy for a premium-priced high-dose obesity treatment and shares in the company fell 4 percent.
Novo Nordisk said subjects with Type 2 diabetes achieved 6 percent weight loss with 3 milligrams of liraglutide in the advanced Phase III trial compared to 5 percent in those on 1.8 mg.
Patients given a placebo also lost 2 percent of their weight, so the placebo-adjusted loss for the higher dose was 4 percent, analysts noted.
"Five and 6 percent is on the low side in efficacy, but it is important to note that it is enough to be approved by the FDA (U.S. Food and Drug Administration)," said Michael Friis Jorgensen, senior analyst at Alm Brand.
He said the share price reaction was harsh but reflected broader uncertainty about Novo's prospects, following an earlier setback for new diabetes drug Tresiba in the key U.S. market.
"We are pleased about the outcome of this trial and look forward to getting the results from the two remaining trials in the SCALE program," said Mads Krogsgaard Thomsen, chief science officer at Novo.
Soren Lontoft Hansen, an analyst at Sydbank, endorsed Thomsen's view, arguing the results were "robust" - but an analyst at a major bank, who asked not to be quoted before he published on the subject, said the results were only "so so".
The fact there was just a marginal benefit from using the highest dose was a particular concern for the company's high-price strategy, he added.
Novo wants to turn the injected drug - already on the market as a treatment for Type 2 diabetes under the brand name Victoza - into a multibillion-dollar-a-year product for the seriously obese.
While some in the industry are skeptical about using so-called GLP-1 diabetes drugs such as liraglutide to fight obesity, Thomsen believes the approach can offer cost-effective benefits.
Glucagon-like peptide-1, or GLP-1, drugs work by stimulating insulin release when glucose levels become too high. Their ability to induce weight loss is an added benefit, since type-2 diabetes is linked to obesity.
Novo Nordisk expects to complete the two remaining Phase III trials in the so-called SCALE clinical trial program by mid-2013.
When used in diabetes as Victoza, liraglutide is given at daily doses of either 1.2 or 1.8 mg. Novo, however, has been betting on a higher dose to produce greater weight-loss in the obese.
Novo Nordisk shares were down 4.2 percent at 8.45 a.m. ET, underperforming a 0.4 percent fall in a European drugs sector index.
(Reporting by Johan Ahlander, Stine Jacobsen and Ben Hirschler; Editing by Tom Pfeiffer)