New Drug Causes 20 Percent Weight Loss in Early Amgen Results

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.”

Dr. Jay Bradner, the company’s chief scientific officer, noted a surprising effect of the drug: When the trial ended, many participants maintained their weight loss for as long as 150 days. That means that less frequent injections could be possible or even that patients may not need to stay on the drug permanently. The company said it was studying quarterly injections.

The patients in the Amgen study who had Type 2 diabetes lost up to 17 percent of their initial weight. That is consistent with findings involving other obesity drugs — people with diabetes tend to lose less weight.

Dr. Bradner also noted that weight loss with the drug did not plateau at 52 weeks. That raises the possibility, he said, that patients may continue to lose weight if they take the drug for a longer time.

Some patients experienced side effects, including nausea that occurred an average of six days and vomiting that began an average of one to two days after starting treatment. In each case, the adverse effects usually resolved themselves.

The Amgen drug acts differently from the main obesity drugs that are currently being sold, Wegovy by Novo Nordisk and Zepbound from Eli Lilly. Those are molecules that bind to a protein on the surface of cells that responds to the gut hormone GLP-1.

But MariTide is different in its structure and function. It is an antibody and, as is typical of those molecules, it lasts longer in the body.

MariTide resembles the earlier drugs because it binds to GLP-1 receptors, using two peptides that stick out from its surface. But it differs in a surprising way because it also blocks the effects of another gut hormone known as GIP. Researchers had thought that the way to make an obesity drug was to activate GIP, not to block it.

Dr. Bradner said the company decided to block GIP because it had genetic data from Iceland indicating that people who had a variant that stops GIP from working were naturally thinner.

Why MariTide is effective remains a mystery. Eli Lilly’s drugs — Mounjaro, for diabetes, and Zepbound, for obesity — activate GIP. So why would Amgen’s new drug work so well?

The company wants to know, too. So it is sponsoring Randy Seeley, director of the University of Michigan’s obesity and nutrition research center, to study mice to try to figure it out.

“It’s weird,” Dr. Seeley said. “It doesn’t fit most of our ideas about how biology is supposed to work.”