Pfizer’s latest multibillion-dollar deal shows it isn’t backing down from the obesity fight. For investors, the stock offers a cheap ticket into the hottest corner of pharma.

After its homegrown obesity pill flopped, Pfizer looked like it was out of the weight-loss race. Patent expirations and the loss of Covid vaccine windfalls left it short of growth drivers, and its shares have fallen nearly 50% in three years—making it one of the industry’s cheapest big names.

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The company’s growth problems aren’t solved yet. But with Monday’s agreement to buy Metsera for up to $7.3 billion, Pfizer is making a shrewd bet that monthly weight-loss shots could open the door to a market now dominated by Novo Nordisk and Eli Lilly.

Metsera, which recently went public, has assembled a portfolio of weight-loss drugs designed to be easier for patients to take than today’s weekly shots. Its lead program is a once-monthly injection in the GLP-1 drug class, the same category as Novo Nordisk’s Wegovy and Eli Lilly’s Zepbound. Early data suggest it can deliver strong weight loss with fewer stomach side effects, and Pfizer expects to move it into late-stage testing next year.

We have seen this movie before, so some caution is warranted. Amgen’s stock surged starting in mid-2023 on hopes that its once-monthly GLP-1 shot could offer convenience without losing effectiveness. But when results released in late 2024 showed high rates of stomach-related side effects and less-than-expected efficacy, the shares plunged.

One reason for optimism is design. Metsera’s lead drug has an unusually long half-life, which makes once-a-month dosing possible. Early trials also show that gradually stepping up from smaller weekly doses before moving to the monthly shot helps patients tolerate it better.

If Metsera’s once-monthly GLP-1 shot can rival weekly competitors without the side effects that sank confidence in Amgen’s effort, Pfizer could have a winning ticket. At today’s rock-bottom valuation, the potential downside looks outweighed by the upside. The stock trades at just 7.7 times forward earnings—roughly half the industry average. In comparison, Eli Lilly fetches 27, Novo Nordisk trades at 15, and Amgen garners 13.

Metsera is set to release 28-week trial data soon, a milestone that could jolt Pfizer’s stock. Leerink analyst David Risinger, who had just initiated coverage of Metsera with an “outperform” rating before Pfizer snapped up the company, estimates its obesity portfolio could eventually generate over $5 billion in peak annual sales—a meaningful lift for Pfizer’s shrinking revenue base as blockbuster drugs like Eliquis and Ibrance go off patent.

Metsera also brings cost and regulatory perks. A once-a-month drug uses far less active ingredient and far fewer injection pens than weekly rivals, meaning it could be cheaper to make and scale. And because it is a peptide of more than 40 amino acids, it is considered a biologic—shielding it from compounding risk and giving it a longer 13-year window before Medicare can negotiate prices, notes Risinger.

Pfizer is joining a crowded field of obesity-drug hopefuls that already includes Roche, AstraZeneca, AbbVie, Amgen and Regeneron. The competition will be fierce, but with Metsera, Pfizer isn’t just buying one shot—it is buying a platform. The company is developing a second injectable that mimics the hormone amylin, which helps regulate appetite and blood sugar. Metsera hopes to combine that with its GLP-1 in a single monthly shot that could rival the best weight-loss results in the category. It is also working on an oral GLP-1 pill in early trials that may avoid the food and water restrictions common to other oral obesity treatments.

The deal won’t fix Pfizer’s growth gap immediately, and success isn’t guaranteed. Still, in a market hungry for new weight-loss options, the company suddenly has a new narrative that investors might find easier to stomach.

Write to David Wainer at david.wainer@wsj.com

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