AbbVie (ABBV -1.52%) is a top healthcare company that's worth nearly $290 billion. It has a diverse business that generates revenue from many different therapeutic areas. Its bread and butter is the immunology drug Humira, which has already brought in a whopping $15.7 billion in revenue through the first nine months of the year.

But Humira has been both its greatest product and the source of the company's greatest worry as investors have become concerned about its patent cliff and a loss in exclusivity that will begin to chip away at its market share as early as next year. So to diversify its business and to help offset some of that risk, AbbVie acquired Botox maker Allergan in 2020 for a whopping $63 billion. Here's how you would have done if you had bought the stock after that deal closed.

AbbVie closed its acquisition of Allergan on May 8, 2020

It has been more than two years since AbbVie completed what it called a "transformative acquisition" of the Botox maker in 2020. The deal diversified AbbVie, giving it a new segment, aesthetics, which could help add significant growth opportunities. At the time the deal was closed, shares of AbbVie closed at $83.96. At that price, investing $25,000 into the healthcare business would have enabled you to purchase approximately 298 shares.

The stock has gone on to soar since then, with shares of AbbVie now trading around $160, nearly double that value. That would make that $25,000 investment now worth around $48,000. And that doesn't factor in the company's dividend, which yields a generous 3.7%. When you factor in that revenue, the investment is worth nearly $54,000.

Why have investors been so bullish on AbbVie?

Over the past few years, AbbVie's business has experienced significant growth. And along with a sharp increase in revenue, which, in part, has been aided by the Allergan acquisition, the company's bottom line has also improved.

ABBV Operating Income (TTM) Chart
Data by YCharts.

As profits grow, a company's valuation will also go up, assuming investors pay similar multiples as they have in the past. In AbbVie's case, investors are now paying more of a premium for the business:

ABBV PE Ratio Chart
Data by YCharts.

Investors now see more value in the company, given its added diversification. Plus, new immunology drugs Skyrizi and Rinvoq reduce some of the risks for investors, as they have generated a combined $5.3 billion in sales this year and management expects that together, their peak revenue will be higher than Humira's. By comparison, the company's revenue from Botox-related products during the same period has totaled just under $4 billion.

With some comfort in knowing that AbbVie's future is a bit safer than it may have appeared to be just a few years earlier, investors have been willing to pay a higher premium for the business.

Is AbbVie still a buy today?

Shares of AbbVie are trading at 14 times their future earnings (based on analyst expectations). That's below the healthcare average of 17, which suggests that AbbVie could be a good buy even with the strong gains it has amassed over the past couple of years. 

Not only does the healthcare stock make for a good growth investment, but its 3.7% yield is well above the S&P 500 average of 1.7%, and it can be an excellent source of recurring revenue for your portfolio. All in all, AbbVie is a solid long-term investment you can buy and hold for years.