Boston biotech Zafgen Inc. released data Thursday showing its experimental weight-loss drug helped patients lose up to a pound a week in an early-stage clinical study.

The compound was well-tolerated by patients with no evidence of side effects that could increase the risk of blood clots, the company said.

Its drug was administered twice a week to dozens of healthy volunteers who were overweight or obese. The volunteers were divided into groups taking different doses of the drug.

Zafgen shares climbed 17 percent to $5.70 in after-hours trading on the Nasdaq stock exchange.

In a statement, Zafgen chief executive Thomas Hughes called the findings “an important first step’’ toward bringing the drug to market. He said the data from the 28-day trial were strong enough to warrant taking the compound to a mid-stage trail, beginning in the second half of this year, where it will be tested on overweight patients with type 2 diabetes.

Last summer, Zafgen suspended development of a separate obesity drug called Beloranib. The company put on hold testing of that drug in 2015 after two patients died during a clinical trial. Zafgen’s stock lost more than 60 percent of its value and the company was forced to cut about a third of its employees.

Robert Weisman can be reached at robert.weisman@globe.com. Follow him on Twitter @GlobeRobW.