Is Eli Lilly's Weight Loss Empire in Trouble?

Over the past two years, Eli Lilly (NYSE: LLY) has established itself as the leader in the weight loss market. That's thanks to the company's tirzepatide, a compound sold under the brand name Zepbound in anti-obesity (and Mounjaro in treating diabetes) that became the best-selling drug in the world in 2025. Zepbound could continue riding the wave of a fast-growing weight loss market for years, but many other companies are looking to eat Eli Lilly's lunch here. Over the past three months, several have posted strong phase 2 or phase 3 results for candidates that could eventually challenge Zepbound. Is Eli Lilly's biggest growth driver in trouble?

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Meet (some of) the competitors

Many pharmaceutical and biotech companies, large and small, are looking to enter this field. Significantly fewer look likely to challenge Eli Lilly seriously. Let's consider three that might be able to. First, there is Regeneron, which partnered with a China-based drugmaker to develop a GLP-1 medicine called olatorepatide. Regeneron owns the rights to commercialize olatorepatide in countries outside of China. Recently, the biotech giant announced that in a phase 3 study conducted in China, patients taking this medicine achieved a mean weight loss of up to 19% after 48 weeks.

There are several notable things here. First, this was a relatively large late-stage study, albeit one conducted in a country outside the U.S. Second, the 19% mean weight loss is comparable to Zepbound's 20.2% weight loss performance in a 72-week phase 3 study. Third, just like Zepbound, olatorepatide is a dual GLP-1/GIP agonist, that is, it mimics the action of those two gut hormones, instead of just one, which can help improve efficacy.

Regeneron is now a real contender in the weight loss race. Then, there is Roche, which posted strong phase 2 study results for its candidate, CT-388, in January. CT-388 is also a dual GLP-1/GIP agonist. In the study, the medicine led to a placebo-adjusted weight loss of 22.5% after 48 weeks. Finally, there is Novo Nordisk. The Denmark-based pharmaceutical giant is also partnering with a Chinese company to develop UBT251, a medicine that mimics the actions of GLP-1, GIP, and glucagon -- a triple agonist. In a recent phase 2 study in China, UBT251 posted a mean weight loss of up to 19.7% in just 24 weeks.

Can Eli Lilly keep the crown?

It's important to note that none of these candidates will hit the U.S. market anytime soon. Novo Nordisk and Roche still need to conduct phase 3 studies for theirs, and while Regeneron's performed well in a pivotal trial, that was in China. This result is unlikely to support approval in the U.S. At best, it will take a couple of years for any of them to challenge Zepbound. But will other therapies enter the market sooner that could do it? Novo Nordisk's CagriSema should be the next one, but it won't pose a significant problem to Eli Lilly.

Novo Nordisk's own study showed that Zepbound was superior to CagriSema. Here's another important reason Eli Lilly's lead is likely intact: The company has its own candidates that are making steady progress. Eli Lilly's oral GLP-1, orforglipron, will likely hit the shelves in the second quarter. And it could capture a market-leading share of the oral weight-loss space, given its phase 3 results across diabetes and obesity, as well as its lack of food or beverage restrictions before taking it.

There is also Eli Lilly's retatrutide, a triple agonist that recently posted an outstanding 28.7% mean weight loss in a study. Yes, the weight loss market will become more competitive, but Eli Lilly should be the biggest beneficiary. Over the next five years, investors can expect the pharmaceutical company to continue posting strong financial results, just as it has recently. Eli Lilly's revenue in 2025 increased 45% year over year to $65.2 billion, while its earnings per share climbed 96% year over year to almost $23.

Further, Eli Lilly's lineup and pipeline are fairly diversified beyond its core therapeutic area. Lastly, the company is investing heavily in technology, notably in artificial intelligence, to speed up the drug discovery process, efforts that could pay off big time down the road. Given Eli Lilly's sustained dominance in the weight management market and the business's other strengths, the stock is still worth investing in.

Prosper Junior Bakiny has positions in Eli Lilly and Novo Nordisk. The Motley Fool has positions in and recommends Regeneron Pharmaceuticals. The Motley Fool recommends Novo Nordisk and Roche Holding AG. The Motley Fool has a disclosure policy.