The pharmaceutical manufacturer Amgen announced on Tuesday that an experimental obesity drug helped patients lose up to 20 percent of their weight in a year. The drug, MariTide, is given by injection once a month, compared with once a week for other obesity drugs like Wegovy and Zepbound that are already on the market.

Those drugs have stunned longtime obesity researchers, who had all but given up on ever seeing safe and effective weight loss drugs. Now, dozens of similar drugs are in development, as companies try to improve on the current ones. Amgen’s is among the first to show what might be possible.

The data came from a Phase 2 trial testing effectiveness as well as safety. It involved nearly 600 people divided into two groups, one with adults who were obese or overweight, and another with patients who also had Type 2 diabetes.

The drug still must go through additional clinical trial phases involving many more patients, and then receive approval from the Food and Drug Administration before being sold to patients. The company has yet to set a price for the drug and did not lay out a timeline for when the drug may become available.

Amgen also did not provide detailed data — that will come in later in a peer-reviewed study and will be presented at a meeting, the company said. Instead, to meet requirements of the federal Securities and Exchange Commission, it provided so called top-line data that could affect its stock price.

Dr. Jeffrey Flier, a diabetes and obesity researcher at Harvard, said the results were “promising,” adding that MariTide “could be a future player in a highly competitive market.”