Eli Lilly (LLY 1.80%) has been around for almost 150 years, finding ways to innovate and grow. Today, it's the most valuable healthcare company in the world, with a market cap of $730 billion.

The next largest healthcare company is UnitedHealth Group, which is worth less than $450 billion. Over the past five years, Eli Lilly's stock has soared by around 530%, soundly beating the S&P 500 and its 136% gain during the same time frame.

Even with such impressive gains in recent years, there is no shortage of reasons to feel comfortable buying and holding the stock for the long haul. Here are five of the best reasons to buy shares of Eli Lilly today and why it's not too late to add it to your portfolio.

1. Eli Lilly has a robust pipeline of drugs with plenty of growth opportunities

What's made Eli Lilly a hot buy in recent years is its GLP-1-related efforts. The company has a couple of GLP-1-approved drugs in Zepbound (weight loss) and Mounjaro (diabetes), and the billions in revenue these drugs may generate in the years ahead has investors bullish on the company's future growth.

However, there's also hope that Alzheimer's drug Kisunla, which regulators approved last year, may also become a blockbuster for the business. And the company is still eyeing more growth opportunities.

Last year, it reached an agreement with Aktis Oncology to develop radiopharmaceuticals, which are more targeted cancer treatments. It's a relatively new type of therapy option for patients, treating specific cancer cells, and just one example of the company's plentiful, robust pipeline.

Eli Lilly has dozens of ongoing clinical trials. With the company's strong commitment to innovation, there may be many more blockbuster drugs in its future.

2. Eli Lilly is investing heavily in U.S. manufacturing to help meet demand

There's no denying that GLP-1 drugs are a big part of Eli Lilly's business today and will be for years to come. The biggest problem these days is to ensure that there's adequate supply. To combat this, the company has been investing heavily in U.S. manufacturing.

Last month, Eli Lilly announced plans to invest $27 billion in four new manufacturing locations, and that's in addition to other investments. Over the past five years, it has announced over $50 billion in manufacturing investments, which CEO David Ricks says is "the largest pharmaceutical expansion investment in U.S. history."

By growing its operations to bolster its supply of drugs, Lilly is reducing the risk that it may miss out on lost sales due to massive demand. It's a good problem to have and an important one to address, and a big reason the company can do so is because of its impressive financials.

3. Eli Lilly's financials are strong, giving it the resources to grow operations

For Eli Lilly to be a top growth stock, having the potential to grow isn't enough. It also needs the resources to take advantage of those opportunities and invest in its operations -- and it has that, as well.

Last year, the company's revenue rose by 32% to more than $45 billion. More importantly, its net income doubled to $10.6 billion, and it generated $8.8 billion in cash flow from its day-to-day operations. Although free cash flow was just $414 million, it came amid some heavy capital spending. In two of the past four years, Eli Lilly's annual free cash flow has been in excess of $4 billion.

With strong financials to help grow its operations, Eli Lilly is in excellent shape to continue reinvesting into its pipeline and future opportunities.

4. Eli Lilly's dividend grows at a high rate, which should continue as earnings rise

An excellent reason to buy and hold shares of Eli Lilly is for its growing dividend. At 0.7%, the stock's yield may look unimpressive, but if not for the healthcare company's rapidly growing valuation, that yield would be much higher. The company has aggressively boosted its payout, and in December, it announced a 15% increase to the dividend -- the seventh year in a row that it has made such a significant boost to its payout.

For long-term investors, a growing dividend can be valuable, especially one that's rising at such a high rate to ensure that recurring income rises at a faster rate than inflation. Plus, it may attract more income-seeking investors in the process, pushing the stock price higher. Even if the rate of increases slows down in the future, there could be many more rate hikes ahead.

5. Its valuation looks attractive, specifically its modest PEG ratio

Eli Lilly stock trades at close to 70 times its trailing earnings, which may dissuade many investors from buying it. They may fear that they've missed out and a sell-off may be overdue.

But based on a price-to-earnings-growth ratio (PEG) of just 1.2, Eli Lilly remains a solid buy, given the growth that analysts expect from the business going forward. When a PEG ratio is around 1, the stock isn't expensive when factoring in its long-term growth. Ideally, the PEG would be less than 1, but the modest multiple makes a good case nonetheless that Eli Lilly stock isn't as expensive as it may appear to be at first glance.

Eli Lilly is a no-brainer buy for the long haul

By now, it should be fairly evident why Eli Lilly is a tremendous growth stock to buy and hold for years. It has a lot of potential to continue to go higher, even though its valuation may seem rich. The company has proven to be a growth machine over the years and can be an excellent investment to put in your portfolio to buy and forget about.