The competition to develop the next blockbuster weight loss drug is heating up, and Pfizer is looking to make a big splash with its own entry.

On Tuesday, Pfizer presented the latest trial data on its ultra-long-acting GLP-1 experimental drug, code-named PF’3944. People taking PF’3944 lost more weight than those on a placebo, the trial showed, even after switching to a monthly schedule. The company will push for more Phase III trials of the drug this year.

A potential leg up

Pfizer acquired PF’3944 as part of its larger purchase of biotech company Metsera, completed last November.

Like current drugs on the market such as semaglutide (Ozempic and Wegovy), PF’3944 mimics GLP-1, a hormone that is important in regulating our hunger and metabolism. But it is designed to stay in the body longer than current GLP-1s, ideally allowing for a less cumbersome dosing schedule.

The Phase 2b VESPER-3 study tested how people fared on PF’3944 after switching to a less frequent dose. The volunteers were obese and overweight people without type 2 diabetes. They were chosen to receive a weekly dose of the drug or a placebo for the first 12 weeks. From weeks 13 to 28, they moved to monthly maintenance shots.

As with other GLP-1 drugs, people taking PF’3944 lost more weight than the placebo group. At 28 weeks, users lost up to 12.3% of their body weight compared to placebo. It appears that there is no bridge in the rate of weight loss in people at week 28, which suggests that the monthly switch does not hinder the effectiveness of the drug and that its peak can be even higher. (For other GLP-1s, maximum weight loss is usually reached in one year). PF’3944 also appears to be generally well tolerated, with the most common adverse events being gastrointestinal, as is common with this class of drug.

“These topline results from the Phase 2b VESPER-3 study reinforce the potential of PF’3944 as a monthly treatment with competitive efficacy,” said Jim List, chief internal medicine officer at Pfizer, in a statement from the company.

What’s next?

The VESPER-3 study is still ongoing and will continue until participants have been on the drug for 64 weeks. But because of the promising results so far from this and other studies, Pfizer is already moving forward with further development.

By 2026, the company will advance 10 Phase 3 trials of PF’3944, testing it as a weekly and monthly injection. Based on previous study data, the company also decided to evaluate the safety and effectiveness of a larger monthly dose to continue some of these tests.

Pfizer isn’t the only biotech trying to gain an advantage in the market by developing more affordable GLP-1 drugs. Amgen’s MariTide—which combines a GLP-1 agonist and a GIP antagonist—is also being developed TESTED as a monthly injection, with more Phase III trials in the works.