Pfizer Halts Development of Daily Weight Loss Pill After Liver Injury in Trial Participant

New York – Pharmaceutical giant Pfizer Inc. has announced it is terminating development of its once-daily experimental weight loss pill, danuglipron, after a clinical trial participant developed a liver injury potentially linked to the medication.

The patient, who was part of a dose-escalation study, showed elevated liver enzymes—a common indicator of liver stress or damage—but did not exhibit any physical symptoms, Pfizer said in a statement. Enzyme levels reportedly returned to normal after discontinuing the drug, which is part of a class of weight-loss medications known as GLP-1 receptor agonists.

Regulatory Input Leads to Discontinuation

The company said its decision followed a comprehensive review of clinical data and discussions with regulatory agencies.

“While we are disappointed to discontinue the development of danuglipron, we remain committed to advancing innovative therapies for obesity,” said Dr. Chris Boshoff, Pfizer’s Chief Scientific Officer.

Danuglipron works by mimicking the GLP-1 hormone, which regulates appetite and blood sugar—similar to injectable therapies like Novo Nordisk’s Wegovy and Ozempic, and Eli Lilly’s Zepbound and Mounjaro.

Setbacks in Pfizer’s GLP-1 Ambitions

The move marks another setback in Pfizer’s bid to enter the rapidly growing weight-loss drug market, expected to top $150 billion by the early 2030s. Oral GLP-1 drugs alone are projected to comprise $50 billion of that total.

This is the second major discontinuation related to danuglipron. In December 2023, Pfizer pulled the plug on a twice-daily version of the pill after patients reported tolerability issues in mid-stage trials.

Despite Monday’s announcement, Pfizer noted that earlier clinical studies for the once-daily danuglipron had met key endpoints, showing competitive efficacy and tolerability among a sample of over 1,400 patients. Still, concerns about liver enzyme elevations were enough to halt further development.

A Shift in Pipeline Strategy

Pfizer emphasized that obesity treatments remain a priority, and the company is pivoting toward next-generation drugs in the space. These include:

• A GIPR-targeting oral drug currently in Phase 2 trials

• A new once-daily oral GLP-1 formulation in Phase 1 testing

The company believes the GIPR-targeting therapy may offer improved efficacy and better tolerability over traditional GLP-1 medications. Former Chief Scientific Officer Mikael Dolsten had previously stated the approach could “unlock broader applications for metabolic health.”

Competitive Landscape Tightens

Pfizer is attempting to close the gap with rivals Eli Lilly and Novo Nordisk, whose injectable GLP-1 therapies dominate the market. As of 2024, Novo Nordisk’s Rybelsus—the only FDA-approved oral GLP-1—generated over $3.38 billion in sales, primarily for Type 2 diabetes treatment.

While Pfizer’s share price has seen modest recovery following the decline of its COVID-19 product line, analysts note that the company’s long-term growth strategy is now increasingly tied to success in oncology and obesity treatments.

Pfizer’s decision to withdraw danuglipron underscores the high-stakes challenges in the race for safe, effective, and convenient weight loss drugs, as the global health industry continues to prioritize treatments for obesity and metabolic disorders.