Prediction: This 1 Thing Could Cement Eli Lilly's Leadership in the Billion-Dollar Weight Loss Drug Market

Eli Lilly (NYSE: LLY) has accomplished something big over the past year. It's become the leading weight loss drug company in the U.S., holding 60% market share. This is as rival Novo Nordisk's market share slipped to 39%. What's helped Lilly step ahead? A study comparing the Lilly drug to the Novo one showed greater weight loss with the former, and Lilly has invested heavily in manufacturing to ensure its products are available.

Still, the competition is far from over. Novo was the first to win approval of its weight loss pill -- oral Wegovy -- and the rollout of that product has been very successful so far. Just recently, Lilly earned the regulatory nod for its oral product, Foundayo, but this comes a few months after the oral Wegovy approval, meaning Lilly must fight a bit harder to carve out its spot.

Now, my prediction is this one thing -- and it's not the oral weight loss drug -- could cement Lilly's leadership in the billion-dollar weight loss drug market. Let's find out more.

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Zepbound and Mounjaro

Lilly already is generating blockbuster revenue thanks to its weight loss portfolio, based on tirzepatide. The company sells this under the name Zepbound for weight loss and Mounjaro for type 2 diabetes. These products are dual GIP/GLP-1 receptor agonists, targeting two hormonal pathways involved in digestion. By doing this, they help regulate blood sugar levels and appetite -- and as a result, the user sheds pounds.

In the most recent quarter, Zepbound and Mounjaro together brought in more than $11 billion. Though Zepbound is meant for those aiming to lose weight, Mounjaro won approval first, and some doctors have prescribed it for this indication as well.

The performance of these drugs helped Lilly's overall revenue soar 43% to more than $19 billion in the three-month period. Soon, Foundayo, approved earlier this month, should add to this bright revenue picture. This drug has one particular advantage over the Novo weight loss pill: Foundayo can be taken with food and beverages, while the Novo drug must be taken on an empty stomach.

But it may not be this drug that extends Lilly's leadership in the weight loss drug market. Instead, the company's next candidate may do the job. I'm talking about retatrutide, a candidate that recently delivered promising results in a phase 3 weight loss and osteoarthritis trial and a phase 3 type 2 diabetes trial.

Seven trial completions in 2026

Lilly expects a total of seven retatrutide for obesity and diabetes phase 3 trial completions this year.

What's so special about retatrutide? This candidate acts on three hormonal pathways -- GIP, GLP-1, and glucagon -- suggesting it may be even more efficacious than current treatments. In the phase 3 trial for weight loss and osteoarthritis, retatrutide resulted in a more than 28% decrease in body weight over 68 weeks. In a head-to-head trial conducted by Lilly over 72 weeks, Zepbound delivered 20% average weight loss while Wegovy delivered more than 13% weight loss. It's difficult to compare results across trials because they aren't necessarily set up in exactly the same manner, but this, along with the fact that retatrutide targets three hormonal pathways instead of one or two, suggests the candidate could result in superior efficacity.

This doesn't mean that all patients will drop their current GLP-1 drugs and opt for retatrutide. It may, for instance, be a fantastic option for those needing to lose a lot of weight, but those aiming to lose fewer pounds may accomplish this just fine on their current drugs. But retatrutide could offer Lilly a very well-balanced portfolio, with options for a variety of patients – and this may reinforce the company's lead in the weight loss market.

So, my prediction is retatrutide may boost Lilly's lead in weight loss, and that makes the company an excellent pharma growth player to hold onto for the long term.

Adria Cimino has no position in any of the stocks mentioned. The Motley Fool recommends Novo Nordisk. The Motley Fool has a disclosure policy.