Pfizer on Tuesday reported promising results from a mid-stage trial of its experimental obesity drug, PF-3944, acquired through Metsera, showing significant weight loss with once-monthly dosing.
In the ongoing phase two study, patients with obesity or overweight lost up to 12.3% of their body weight compared with placebo at week 28. When considering all participants, regardless of discontinuations, weight loss reached 10.5%. Notably, Pfizer reported no plateau in weight loss after transitioning patients to monthly injections, suggesting continued efficacy through the study’s planned 64-week duration.
“The data are very good, and we are saying one clear thing: we have a monthly product that has a very competitive profile in tolerability and efficacy,” Pfizer CEO Albert Bourla told CNBC.
The drug’s monthly schedule could provide a competitive edge in the obesity treatment market, currently dominated by Eli Lilly and Novo Nordisk, which offer weekly injections and, in Novo’s case, a daily oral pill. Pfizer executives noted that patients already using injectable GLP-1 drugs are unlikely to switch to daily oral alternatives, making less frequent injections an attractive option.
“Weekly doesn’t work for everybody,” said Dr. Jim List, Pfizer’s chief internal medicine officer. “Some patients need to travel and can’t keep their injections refrigerated. PF-3944 is going to help expand the market and offer a more convenient maintenance option.”
Pfizer plans to launch 10 phase three trials for PF-3944 this year. Modeling predicts that a higher monthly dose in late-stage trials could yield up to 16% weight loss at week 28, potentially offering efficacy that Bourla described as “maybe best in class.”
The company’s injection is an ultra-long-acting GLP-1 drug, engineered to remain active in the body longer than current treatments such as Novo’s Wegovy. In the phase two trial, patients initially received weekly injections for 12 weeks before switching to monthly dosing, which was well tolerated. Most gastrointestinal side effects were mild or moderate, and no new safety concerns were reported.
Pfizer selected two monthly maintenance doses—low and medium—for upcoming phase three studies. In phase two, five patients discontinued during the weekly phase and another five during the monthly phase due to side effects.
The announcement coincided with Pfizer’s fourth-quarter earnings, which beat revenue expectations, though shares closed nearly 3% lower.
Pfizer’s experimental injection is being developed not only as a weekly and monthly option but also in combination with other treatments targeting gut hormones, offering patients more flexibility in obesity management.
