AbbVie (ABBV 0.90%) wowed investors last year when it outperformed the S&P 500 index. Shares of the pharmaceutical company climbed 19%, while the benchmark fell by as much.

Since the start of the year, though, AbbVie shares have lost momentum. Why? The company's blockbuster immunology drug, Humira, is facing competition -- and that means sales are set to fall.

At the same time, AbbVie's full portfolio of other blockbusters and a pipeline of promising candidates give us reason to be positive about the company. So what should investors do? Let's look at two reasons to buy AbbVie right now -- and one reason to sell.

Reason to buy: Two new growth drivers

AbbVie has been preparing for Humira's loss of exclusivity by developing two other immunology drugs that may take over where Humira's leaving off. The company aims to win approval for Rinvoq and Skyrizi in all of Humira's indications and more.

So far, Rinvoq has won the regulatory nod for five indications, and Skyrizi for three. Additional decisions should be on the way. The U.S. Food and Drug Administration (FDA) is reviewing Rinvoq for Crohn's disease, and Skyrizi is involved in a phase 3 trial for ulcerative colitis.

These drugs already are bringing in blockbuster revenue, and the company predicts that, together, they'll generate $17.5 billion in 2025. And AbbVie forecasts they'll reach more than $21 billion in revenue in 2027. That means that, together, they may beat Humira's peak revenue of more than $20 billion.

AbbVie's immunology business should continue to boom -- with or without Humira.

Reason to buy: The financial picture

AbbVie completed its purchase of Allergan back in 2020. The $63 billion deal brought significant growth drivers -- such as an aesthetics portfolio led by top wrinkle treatment, Botox.

The great news is that AbbVie is benefiting from the growth of Allergan products and has aggressively cut the debt associated with the deal. The company says it's on track to extinguish incremental debt linked to the purchase by the end of this year.

At the same time, AbbVie has continued increasing its dividend, making it a solid choice for investors seeking passive income. The quarterly dividend has climbed by 270% since the company's beginnings. AbbVie pays an annual dividend of $5.92 a share, which translates to a dividend yield of 3.79%. That's higher than the industry average of 2.15%, according to the NYU Stern Business School.

AbbVie's financial picture is definitely a bright one for investors.

Reason to sell: A difficult near term

Yes, the rest of the immunology portfolio and AbbVie's other products should compensate for the loss of Humira. AbbVie predicts a return to strong sales growth by 2025. But the near term -- this year and next year -- may be difficult for the company.

AbbVie expects a 37% drop in U.S. Humira sales this year. The drug already has been facing competition internationally, where last year, sales slipped 22%.

Investors will have to be patient and wait through this period of declining revenue for newer drugs to compensate and eventually even outperform Humira. Meanwhile, the stock price could stagnate. And that means you may gain more by placing your money elsewhere.

Should you buy or sell?

I think the reasons to buy are stronger than the reason to sell. Yes, AbbVie stock may not soar in the near term, but the company is setting the stage for major earnings growth over time. Meanwhile, those who invest today can pick up the stock at a reasonable price and benefit from passive income. So even though AbbVie stock probably won't jump overnight, long-term investors still may cheer over their purchase right away -- and over time.