Pfizer is ending the development of its potential once-daily pill treatment for obesity after venturing into the biggest and most expensive level of clinical testing.

The drugmaker said Tuesday that it would stop studying danuglipron after a participant in one of its trials experienced a possible drug-induced liver injury that was resolved once the person stopped taking the drug.

Danuglipron was in phase three testing, which is generally the last phase of development before a company submits the potential treatment to government regulators for approval.

A company official said in a statement that Pfizer still plans to develop other potential obesity treatments in earlier stages of testing.

Obesity treatments have become one of the more promising and lucrative sectors of drug development for pharmaceutical companies. Eli Lilly and Co.'s Zepbound, for instance, brought in nearly $5 billion in sales in 2024, its first full year on the market.

But leading treatments like Zepbound and Novo Nordisk's Wegovy are injectable, and drugmakers are eager to develop an easier-to-take pill version.

Pfizer had announced in late 2023 that it would abandon a twice-daily version of danuglipron after more than half the patients in a clinical trial stopped taking it.

Shares of New York-based Pfizer Inc. slipped 7 cents to $21.84 before markets opened Monday.