Small-cap stocks have more upside potential since they are riskier assets, so investors demand higher rates of return when investing in them. However, large-cap stocks — even those at or near a $1 trillion valuation — can have plenty of room to run, too. That seems to be the case with Eli Lilly (NYSE: LLY), a pharmaceutical giant firing on all cylinders. As of this writing, the drugmaker's market cap is $858 billion, but its prospects look incredibly attractive, particularly because of its involvement in the lucrative market for weight loss drugs. Could Eli Lilly make millionaires out of investors at current levels? Let's find out.

The power of weight loss drugs

Eli Lilly developed a medicine called Zepbound to help with weight loss. It is one of the leading products in this niche, and it is currently posting incredibly fast-growing sales. Despite being approved within the past year, in November 2023, Zepbound is already a blockbuster drug. Medicines typically take years to get to this level, at least the ones that do get that far. Most never do. Why is Zepbound so successful? Several reasons. First, obesity is a severe crisis, especially in the U.S., which has one of the highest obesity rates worldwide.

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Of note, the U.S. is by far the largest pharmaceutical market in the world, accounting for about 44.4% of spending as of last year. Any therapy that targets a condition as prevalent as obesity in the country will likely be somewhat successful. Further, obesity is linked to several of the leading causes of death in the U.S., including heart disease, diabetes, and several forms of cancer. Lowering obesity rates, a goal Zepbound could help achieve, would decrease mortality across these other areas.

A recent study found that expanding access to weight loss drugs like Zepbound could help save more than 40,000 lives annually in the U.S.

No end in sight for this tailwind

Here's what this could mean for Eli Lilly and its shareholders. First, the company will routinely deliver outstanding financial results. Once a pharmaceutical giant's revenue growth rate is in the mid-teens, that's already excellent. These past few years, Eli Lilly's top-line growth was somewhat disrupted by pandemic-related factors. However, the company's revenue growth has been outstanding over the past 12 months. Zepbound will help it maintain that momentum.

However, Eli Lilly's success in weight loss also stems from the fact that it is a new field with few competitors beyond Novo Nordisk's Wegovy. What would happen if other companies developed more effective therapies and ate Eli Lilly's lunch? That shouldn't be a major concern. There will be more competition, but drugmakers often specialize in one or a few specific therapeutic areas. Success in developing drugs in one field leads to more success. Don't underestimate the power of past successes (and failures) in developing novel medicines.