Achieving a trillion-dollar market cap is a significant milestone for any business. It's an exclusive club that includes top companies such as Apple and Microsoft. Companies worth $1 trillion are among the best of the best, and owning a stock that could be worth that much in the future could mean a huge return for investors.

There isn't a healthcare company worth $1 trillion today, but could Eli Lilly (LLY 0.74%) reach that valuation by 2030? Its market capitalization today is around $315 billion, so it would need to more than triple in value in seven years for it to be worth that much. Below, I'll look at how probable that is and whether the stock is worth investing in right now.

How Eli Lilly could hit a $1 trillion market cap

Last year, Eli Lilly reported $28.5 billion in revenue, which was flat from the previous year. At 10 times revenue, the stock is arguably trading at a bit of a premium. But there's one drug in its portfolio that has the potential to be a game changer for its business, and that's Mounjaro.

If you've seen the ads and all the excitement on social media about Ozempic and Wegovy, then picture Mounjaro -- on an even bigger scale. That's because while weight-loss treatment Wegovy (Ozempic is similar but available in smaller doses, and it's approved for diabetes and not weight loss) has been effective in cutting a person's body fat by an average of 15% (and one-third of people have lost 20% of their weight), Mounjaro has shown that it can reduce a person's weight by up to 22.5%.

Mounjaro is approved for type 2 diabetes but not weight loss yet; however, approval for that indication could come as early as this year. If that happens, Mounjaro has the potential to be the most highly valued drug in the world, as it can possibly treat other obesity-related illnesses as well.

There's a big need for effective weight-loss treatments, and if Mounjaro can be the big winner some analysts are expecting it to be, it wouldn't be out of the question for Eli Lilly to double or maybe even triple sales by the end of the decade. Estimates for Mounjaro range between $25 billion to as high as $100 billion in peak annual sales. The company also has other drugs in its pipeline that can pad its top line, including its Alzheimer's treatment donanemab -- which is another multibillion-dollar opportunity for the business.

Today, Eli Lilly trades at a multiple of 10 times revenue. Assuming that multiple remains intact, then Eli Lilly's revenue would need to be at around $100 billion for the stock to be worth $1 trillion. If, however, it commands a higher multiple because of the stronger growth outlook, then perhaps investors would pay 15 times revenue. At that level, Eli Lilly's sales would need to reach around $67 billion.

Eli Lilly should reach $1 trillion, it's only a matter of when

Eli Lilly has established itself as one of the top drugmakers in the world. With some promising assets in its portfolio such as Mounjaro and donanemab, I'm optimistic that its sales could take off in the future. It's really just a question of how fast -- and whether by 2030 the company's financials will be strong enough for the business to command a $1 trillion market capitalization.

I believe it will reach that valuation by 2030 simply because investors have often paid a premium for the stock; its price-to-earnings multiple is at nearly 50. Between the growth it will achieve by then and Mounjaro potentially being a big hit, it's not unrealistic to expect Eli Lilly's valuation might top $1 trillion by the end of the decade.

Eli Lilly's strong growth prospects make it a top investment. That's why, while the stock may appear expensive today, it can still be a great buy in the long run as Eli Lilly's business is poised to get much bigger.