Pfizer on Tuesday said its experimental obesity drug, which it acquired through Metsera, drove solid weight loss when taken once a month in a mid-stage trial.

Patients with obesity or who are overweight lost up to 12.3% of their weight compared with placebo at week 28 in the ongoing phase two study. The injection’s weight loss was up to 10.5% when analyzing all patients regardless of discontinuations.

The company said no plateau was observed after patients transitioned to monthly dosing, which suggests that continued weight loss is expected as the study continues through week 64.

The data offer early evidence that the injection can be administered less frequently than existing drugs without sacrificing efficacy, which could be a major boost for Pfizer after it faced several setbacks in developing obesity drugs. It’s trying to enter a market dominated by Eli Lilly and Novo Nordisk‘s weekly injections, with a strong new entrant in Novo’s daily pill.

While it’s unclear how much Pfizer could cut into their market share once the shot is available, monthly dosing could offer a more convenient option for patients.

“These topline results … reinforce the potential of PF’3944 as a monthly treatment with competitive efficacy,” said Dr. Jim List, Pfizer’s chief internal medicine officer, in a release.

Pfizer plans to advance 10 phase three trials on the injection, called PF’3944, this year. In prepared remarks for Pfizer’s earnings call later Tuesday, the company’s Chief Scientific Officer Chris Boshoff said that modeling predicts that a higher monthly dose of the injection that Pfizer plans to use in late-stage trial could result in 16% weight loss at week 28.

Pfizer announced the results on the same day it posted fourth-quarter earnings and revenue that topped expectations. Shares of Pfizer fell nearly 3% in premarket trading Tuesday.

The company’s injection is an ultra-long-acting GLP-1 drug, meaning it is engineered to remain active in the body for longer than existing treatments like Novo’s Wegovy. Pfizer is developing it as both a weekly and a once-monthly injection, as well as in combination with other treatments that target different gut hormones.

In the trial, patients started on weekly injections of the drug for 12 weeks before switching to once-monthly dosing.

The study was designed to test whether different doses of the drug could help patients continue their weight loss after switching from weekly to monthly injections. It also examined whether higher doses of the drug could be given monthly while remaining tolerable for patients.

The drug was generally well tolerated by patients, with most gastrointestinal side effects reported as mild or moderate. That’s consistent with other GLP-1 drugs.

Pfizer said there were no new safety issues.

The company said it had selected two dosing regimens — a low and medium monthly maintenance dose — to be tested in phase three trials. Across the two dosing regimens in the phase two trial, five patients discontinued treatment due to side effects during the weekly phase of the trial, while another five stopped the drug during the monthly phase. 

In a separate mid-stage trial last year, Metsera said the highest dose of the injection demonstrated weight loss of up to 14.1% on average after 28 weekly doses.