Pfizer scraps daily weight loss pill after liver injury in one patient

Pfizer on Monday said it would end development of its experimental daily weight loss pill after a patient experienced a liver injury that was potentially caused by the drug in a trial. 

The patient did not experience any liver-related symptoms or side effects, a Pfizer spokesperson said in a statement. They added that the patient’s liver enzymes “recovered rapidly” after they stopped taking the pill, which is an oral GLP-1 drug called danuglipron. The statement suggests that the patient’s liver enzymes were elevated, which often indicates damage to cells in the organ and is an issue that has been linked to some other obesity drugs.

The case occurred in a trial that quickly increased the dose of the pill over a short period of time, the spokesperson said. Pfizer’s decision to halt development of the drug came after “a review of the totality of information, including all clinical data generated to date for danuglipron and recent input from regulators,” according to a release.

“While we are disappointed to discontinue the development of danuglipron, we remain committed to evaluating and advancing promising programs in an effort to bring innovative new medicines to patients,” Dr. Chris Boshoff, Pfizer’s chief scientific officer, said in the release. He added that the company is still developing other weight loss drugs.

The announcement adds to a string of setbacks in the company’s bid to win a slice of the booming market for GLP-1s, which mimic certain gut hormones to tamp down appetite and regulate blood sugar. Pfizer is among several drugmakers racing to bring a more convenient weight loss medicine to a space dominated by weekly injections, but it is years behind competitors such as Eli Lilly and Novo Nordisk.

Some Wall Street analysts expect the GLP-1 industry to be worth more than $150 billion by the early 2030s. Oral GLP-1s could grow to be worth $50 billion of that total, while injections would account for the rest, according to some analyst estimates.

This is not Pfizer’s first set back with danuglipron, specifically, either. The company discontinued a twice-daily version of the pill in December 2023 after patients had trouble tolerating the drug in a mid-stage study.

But Pfizer appeared to be confident in the once-daily form of danuglipron back in July, when it said it would start conducting studies in the second half of the year to evaluate multiple doses of the pill.

Despite its decision to scrap the drug, Pfizer on Monday said those studies met key goals and confirmed a certain form and dose of the pill with the potential to deliver “competitive efficacy and tolerability” in late-stage trials.

The company also noted that the rate of elevated liver enzymes in people who have taken danuglipron is in line with approved GLP-1 drugs, which is based on a safety database of more than 1,400 patients who have taken Pfizer’s pill.

Pfizer scrapped a different once-daily obesity pill back in June 2023 after patients who took that drug had higher liver enzyme levels in a mid-stage trial. Investors have been pessimistic about the company’s potential in the GLP-1 space ever since.

Still, Pfizer has other experimental obesity drugs in its pipeline in the early stages of development that appear to work differently from its now-discontinued treatments. That includes an oral drug that blocks another gut hormone called GIPR, which entered phase two trials last year, and an additional once-daily oral GLP-1 in phase one trials.

Pfizer believes a drug targeting GIPR could be more effective and easier for patients to tolerate, former Chief Scientific Officer Mikael Dolsten, who has since left the company, told investors in October. He added that “there are so many applications for GLP-1s.”

Pfizer’s danuglipron promotes weight loss by targeting GLP-1, which is also how Novo Nordisk’s weight loss injection Wegovy and diabetes treatment Ozempic work. Eli Lilly’s weight loss injection Zepbound and diabetes shot Mounjaro target GLP-1 but also activate another gut hormone called GIP.

The only oral GLP-1 approved by the Food and Drug Administration so far is Novo Nordisk’s Rybelsus, which treats Type 2 diabetes and raked in about $3.38 billion in sales in 2024.

Pfizer’s announcement Monday comes as the company regains its footing and recovers its share price after the rapid decline of its Covid business. Pfizer is betting on its pipeline of cancer drugs to deliver long-term growth, but has emphasized that obesity is a key focus.