Patients given a monthly injection of Amgen’s drug, dubbed MariTide, lost up to 14.5% of their body weight in just 12 weeks, according to a small, early-stage study published Monday in the journal Nature Metabolism. And some people kept the weight off for up to 150 days after stopping the drug, findings show.

“That is really a remarkable and distinguishing characteristic of this molecule,” , senior vice president of global development at Amgen, said in an interview.

Investors and analysts have been eagerly awaiting updates on Amgen’s shot since the Thousand Oaks, California-based company shared early results at a conference in 2022. The latest Nature Metabolism study offers the most detailed look yet at Amgen’s drug, which is now in mid-stage studies. Another readout is expected later this year. 

Amgen’s drug works a bit differently than Wegovy or Zepbound. It’s what’s known as an antibody-drug conjugate, or ADC, a type of molecule more commonly used as a targeted cancer treatment. One part of the drug, an antibody, blocks the GIP receptor, while the other part, two peptides, mimics a gut hormone called GLP-1. 

“There’s something special about having them glued together the way they are on the same molecule,” said Saptarsi Haldar, vice president of cardiometabolic disorders at Amgen. The antibody component of the drug also allows it to stick around in the body longer than weekly weight-loss shots. 

Amgen designed the drug specifically as a treatment for obesity, but is now testing it in patients with diabetes — the opposite of how weight-loss drugs came to be at Eli Lilly and Novo Nordisk. The decision to inhibit GIP, rather than mimic it like Eli Lilly’s Zepbound, was based on insights gleaned from its expertise in human genetics.

“Those genes told us loud and clear that decreased activity of the GIP receptor was associated with decreased BMI, or body-mass index,” Haldar said. 

Amgen’s study, which enrolled 110 patients with obesity, was intended to assess MariTide’s safety and tolerability, but it revealed the drug’s dramatic effects on weight. Patients in one group were randomly assigned to receive a single dose of MariTide and were followed for 150 days, while another group of patients were given a dose every four weeks for three months.

Patients who received a single shot of the highest dose had lost up to 8.2% of their body weight after 92 days, suggesting the drug has a prolonged weight-loss effect, according to the study. 

Safety and side effects were similar to other GLP-1 drugs, findings show. Nausea and vomiting were the most commonly reported side effects and typically lasted for about 72 hours. Four patients in a group receiving the highest dose of the drug withdrew before getting a second shot due to mild gastrointestinal issues, according to the study.

Although the early results are promising, more studies are needed before the drug reaches patients. Honarpour said the results of the company’s mid-stage study are an important next step. Still, Amgen sees ample opportunities for newcomers like itself to enter the obesity market, and is also working on an oral weight-loss drug with results expected in the first half of the year.