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Pfizer Cancels New Weight Loss Pill After Patients Experience Serious Side Effects

Pfizer's new experimental weight-loss pill worked in achieving its stated goal — but with that weight loss came side effects so gnarly that it's shutting down the research.

In a press release, the pharmaceutical giant said it was discontinuing clinical trials for danuglipron, its twice-daily weight loss pill that uses a similar mechanism to semaglutide, because a large percentage of the people who took it in its first two experimental phases experienced gastrointestinal side effects like nausea and diarrhea.

"While the most common adverse events were mild and gastrointestinal in nature consistent with the mechanism, high rates were observed (up to 73% nausea; up to 47% vomiting; up to 25% diarrhea)," the press release reads. "High discontinuation rates, greater than 50%, were seen across all doses compared to approximately 40% with placebo."

Like semaglutide, the active ingredient in the uber-popular Ozempic and Wegovy injectables, danuglipron is a glucagon-like peptide-1 (GLP-1) receptor agonist, the exact mechanism is up for debate but which on a broad level is understood to mimic the feeling of fullness in the gut. Though semaglutide injections — which only in the past few years became approved for weight loss — are so trendy that pharmacies are struggling to keep them in stock, they too can have some major gastrointestinal side effects.

With the popularity of semaglutide injectables came a growing drive to find a way to get the drug's effects in pill form. Until Pfizer decided to discontinue its trials, danuglipron seemed poised to be the next big thing in weight loss treatment — especially considering that prior study results suggested it was as effective as Ozempic.

Not one to give up the goat, Pfizer said in its statement that although it's discontinuing danuglipron trials, it's still seeking to release a weight loss pill.

"Results from ongoing and future studies of the once-daily danuglipron modified release formulation will inform a potential path forward with an aim to improve the tolerability profile and optimize both study design and execution," Dr. Mikael Dolsten, Pfizer's chief scientific officer and president of its research and development wing, said in the statement.

Regardless of its future intentions, the pharma giant's stock did fall four percent after news of danuglipron's crappy side effects dropped.

More on weight loss drugs: Scientists Say Semaglutide Appears to Help Alcoholics, Too