The Most Overlooked Reason Eli Lilly Stock Keeps Surging -- and It Has Nothing to Do With Weight Loss

Eli Lilly (NYSE: LLY) was second to market with a GLP-1 weight-loss drug, losing out to Novo Nordisk (NYSE: NVO). However, Eli Lilly's Mounjaro and Zepbound produce stronger weight-loss results than Novo Nordisk's Wegovy, and they quickly took the lead. Now, many on Wall Street see Eli Lilly as a GLP-1 stock, which it is. But that's not the full picture, as investors are overlooking a much broader business.

How important are GLP-1 drugs to Eli Lilly?

Eli Lilly has a GLP-1 weight-loss drug problem. The company's highly successful Mounjaro and Zepbound accounted for nearly two-thirds of its revenues in the first quarter of 2026. And with year-over-year revenue growth of 125% and 80%, respectively, these two drugs are clearly the driving force behind the company's earnings. It is understandable that Wall Street is highly focused on this segment of the business.

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Being so heavily dependant on two drugs is a risk. For starters, the pharmaceutical sector is intensely competitive. Other drug companies are working on competing products. Secondly, drugs have limited patent protection, so the windfall here is time-limited even in the best-case scenario. While the GLP-1 story is strong for now, it can't sustain the stock forever.

This is why it is so good to see that Eli Lilly has been using the cash it is generating from GLP-1 drugs to buy other companies. It is, effectively, building its pipeline well ahead of the time when it will face GLP-1 patent expirations. For example, it recently inked a $2.8 billion deal to buy AtaiBeckley, which is working with psychedelic drugs.

Eli Lilly has created a position in immunology and more

One area where Eli Lilly is building a strong portfolio is immunology. Essentially, these drugs help people when their own autoimmune systems start attacking their bodies. Eli Lilly is specifically working in Crohn's disease, ulcerative colitis, dermatology, and rheumatoid arthritis. Ebglyss is a key drug in the space, with first-quarter 2026 sales rising 141% year over year.

The company has a number of immunology drug trials underway, as well, that it hopes will lead to new products. And it has been using acquisitions to bolster its plans here, with the early 2026 agreement to purchase Ventyx Biosciences a recent highlight. Ventyx Biosciences had a number of promising drug candidates in its pipeline, so this acquisition helps to build what Eli Lilly hopes will be a strong platform for growth beyond its current GLP-1 portfolio.

And this is just one area among many. Eli Lilly is also using its GLP-1 cash bonanza to invest in oncology and neuroscience. And, more importantly, it is starting to see early signs of success. In the first quarter, key drugs from these niches and immunology saw revenue growth of 160%. The company's success in non-weight-loss drug areas is simply being overshadowed by the sheer size of its GLP-1 business.

Eli Lilly is doing what it should be doing

There's no question that Eli Lilly's business is being driven by GLP-1 drugs right now. However, the company isn't resting on its laurels; it is using its GLP-1 success to invest in other areas, like immunology. And it is seeing material success in the effort. If you are looking at Eli Lilly today, don't focus solely on its GLP-1 drugs. Pay very close attention to what those highly profitable GLP-1 drugs are allowing the drug maker to do with the rest of its business. When it comes to drug companies, the most profitable drugs being sold today aren't always the best indicator of what the future holds for investors.

Reuben Gregg Brewer has no position in any of the stocks mentioned. The Motley Fool has positions in and recommends Eli Lilly and Novo Nordisk. The Motley Fool has a disclosure policy.