Pfizer’s Monthly Obesity Shot Shows Wegovy-Like Side Effects in Midstage Trial, Offering Convenient Dosing Option

Published: June 7, 2026 | New Orleans, LA

NEW ORLEANS — On Saturday at the American Diabetes Association (ADA) Scientific Sessions, Pfizer presented highly anticipated Phase 2b data for its experimental monthly obesity injection, berobenatide. The trial revealed a side-effect profile strikingly similar to Novo Nordisk’s widely used weekly shot, Wegovy. The findings reinforce the drug’s potential as a highly competitive, more convenient alternative in the rapidly growing weight-loss medication market, giving patients the option of substantially fewer injections.

Key Findings from the VESPER-3 Study

The Phase 2b VESPER-3 study evaluated berobenatide (formerly known as PF-3944 and MET-097i), an ultra-long-acting glucagon-like peptide-1 (GLP-1) receptor agonist that Pfizer acquired through its $10 billion purchase of biotech firm Metsera in 2024.

The trial monitored participants over 28 weeks to assess both weight reduction and tolerability:

• Significant Weight Loss: Participants achieved up to 12.3% placebo-adjusted weight loss at 28 weeks on the medium monthly dose of 4.8 mg. Those on the lower monthly dose (3.2 mg) achieved a 10% placebo-adjusted weight reduction.

• Sustained Trajectory: When analyzing all patients—including those who discontinued treatment—the overall weight loss averaged approximately 10.5%. Crucially, researchers detected no weight-loss plateau after participants transitioned from weekly to monthly dosing, suggesting that weight loss could continue through the trial’s full 64-week timeline.

• Manageable Gastrointestinal Profile: The mean nausea rate across all study arms was approximately 38%. However, gastrointestinal (GI) adverse events were predominantly mild to moderate. Only one instance of severe nausea or vomiting occurred across all dosage groups, and no severe cases of diarrhea were reported.

• Discontinuation Rates: In total, five participants discontinued treatment due to side effects during the initial weekly titration phase, and an additional five stopped during the monthly maintenance phase.

What Makes Monthly Dosing Significant?

The ability to administer an obesity medication once a month rather than once a week represents a potential paradigm shift in patient convenience and compliance. Current market leaders, such as Novo Nordisk’s Wegovy (semaglutide) and Eli Lilly’s Zepbound (tirzepatide), require rigid weekly injection schedules.

“The data indicates our monthly product has a competitive profile for tolerability and efficacy,” said Pfizer CEO Albert Bourla during an earlier investor call.

Jim List, Pfizer’s Chief Internal Medicine Officer, echoed this optimism at the ADA sessions: “Our Phase 2b VESPER-3 results reinforce PF-3944’s potential as a monthly obesity treatment with competitive efficacy and tolerability.”

How Berobenatide Compares to Existing Weight-Loss Drugs

While berobenatide offers a clear advantage in dosing frequency, its midstage weight-loss numbers appear slightly lower than Eli Lilly’s market-leading dual-hormone injection, Zepbound, at a similar time point. However, its tolerability aligns closely with the established GLP-1 class.

Independent data underscores that gastrointestinal side effects are a universal hallmark of these medications. For instance, in the landmark SURMOUNT-5 head-to-head trial, roughly 44% of patients taking either weekly tirzepatide or weekly semaglutide experienced nausea, making berobenatide’s 38% nausea rate highly comparable.

Understanding GLP-1 Receptor Agonists and Side Effects

To understand why these side effects occur, it helps to look at how the drugs function. GLP-1 receptor agonists work by mimicking a natural metabolic hormone that regulates appetite and food intake in the brain. They also slow gastric emptying—meaning food stays in the stomach longer. While this mechanism effectively increases feelings of fullness and naturally reduces calorie consumption, it frequently triggers the digestive system.

According to manufacturer safety data, common side effects across the GLP-1 drug class include:

• Nausea and vomiting

• Diarrhea or constipation

• Abdominal pain

• Fatigue and headache

In previous clinical trials for semaglutide, nausea was generally transient and rarely led to permanent discontinuation. However, persistent GI side effects have driven up to 8% of patients to stop taking weekly injections entirely. A monthly formulation with a similar side-effect profile could offer a more manageable experience for individuals prone to “injection fatigue.”

Public Health Implications and Next Steps

Obesity currently affects approximately 40% of adults in the United States, driving up rates of type 2 diabetes, cardiovascular disease, and joint disorders. Introducing a monthly dosing option could radically improve long-term treatment adherence, as patients often find it easier to stick to a twelve-times-a-year regimen than a fifty-two-times-a-year one.

Looking ahead, Pfizer plans to aggressively advance its clinical development pipeline by launching several late-stage Phase 3 programs:

• VESPER-4: Evaluating once-weekly berobenatide in individuals with obesity who do not have type 2 diabetes.

• VESPER-5: Assessing weekly dosing in patients with type 2 diabetes, utilizing a higher 2.4 mg dose.

• VESPER-6: Investigating the once-monthly formulation specifically for long-term weight management in individuals with obesity or overweight.

Anticipating Higher Doses

Pfizer is also aiming for higher efficacy. Chris Boshoff, Pfizer’s Chief Scientific Officer, stated that predictive mathematical modeling indicates a higher monthly dose planned for late-stage trials could yield up to a 16% weight loss at week 28. If realized in clinical settings, this would position berobenatide neck-and-neck with current market leaders.

Study Limitations and Considerations

Despite the enthusiasm surrounding the ADA presentation, medical experts emphasize several caveats:

• Interim Data: The 28-week data represents mid-trial results. The VESPER-3 study is ongoing and must reach its full 64 weeks to establish definitive long-term safety, sustainability of weight loss, and permanent discontinuation rates.

• Slightly Inferior Initial Efficacy: Several industry analysts noted that berobenatide’s raw weight reduction at 28 weeks remains below the benchmarks set by Eli Lilly’s Zepbound at a comparable timeframe.

• Investigational Status: Berobenatide remains an experimental compound. It has not yet been approved by the U.S. Food and Drug Administration (FDA) or any other global regulatory authority for public use.

What This Means for Patients

For people navigating obesity or overweight, these developments signal a future with more personalized medical choices. However, healthcare professionals stress that the decision to start any GLP-1 medication requires a comprehensive consultation. Patients and their doctors must carefully evaluate individual health histories, underlying contraindications, insurance coverage, and the necessity of accompanying lifestyle modifications, such as nutrition and exercise.

Ultimately, the similar side-effect profiles suggest that patients who tolerate weekly injections well may transition easily to monthly options in the future, while those with severe GI sensitivities will still need to plan mitigation strategies with their care teams.

Medical Disclaimer

This article is for informational purposes only and should not be considered medical advice. Always consult with qualified healthcare professionals before making any health-related decisions or changes to your treatment plan. The information presented here is based on current research and expert opinions, which may evolve as new evidence emerges.

References

• Reuters Health. “Pfizer’s monthly obesity shot has side-effect profile similar to Wegovy in midstage trial.” June 6, 2026.