Dividend stocks can be a great source of passive income, and fortunately, there is no shortage of dividend-paying companies in the stock market. However, finding those whose businesses -- and payouts -- will remain intact through bull and bear markets can be a bit of a challenge. After all, many companies slash, or outright suspend, their dividends once the economy stops working in their favor. If you are looking for dividend stocks that can pay you for the rest of your life, rest assured: They exist. Two that I think fall seamlessly into this group are healthcare giants AbbVie (NYSE:ABBV) and Amgen (NASDAQ:AMGN).

Both of these drugmakers have been around for quite some time. AbbVie split from its former parent company, Abbott Laboratories, in January 2013. When considering its run under Abbott, AbbVie has been around for several decades. The same applies to Amgen, which was founded in 1980. The fact that these companies have been able to remain in business for this long doesn't guarantee them a bright future. Still, it is worth noting that they do have a solid and proven history.

And with the need for innovative medicine always increasing, especially given our aging worldwide population, both have an opportunity to continue profiting from their (thus far) successful business models for many years to come. With this backdrop in mind, let's take a closer look at each of these companies.

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1. AbbVie 

Dividend-seeking investors tend to look for companies with the ability to continue generating growing revenue and profits. AbbVie looks well positioned to do just that. The drugmaker's lineup features several medicines whose sales are growing fast. For instance, there is plaque psoriasis medicine Skyrizi and rheumatoid arthritis (RA) treatment Rinvoq. During its first quarter ending March 31, AbbVie's revenue from Skyrizi jumped by 91% year over year to $574 million.

Meanwhile, sales of Rinvoq were $303 million, more than doubling compared to the year-ago period. Both of these drugs will be important for AbbVie's future as the company looks to make up for the declining sales of Humira in Europe. Revenue from the RA drug has been dropping abroad due to competition from biosimilars. Still, sales of Humira continue to climb in the U.S.

In the first quarter, Humira's U.S. sales grew by 6.9% year over year to $3.9 billion; its total sales for the period increased by 3.5% year over year to $4.9 billion. By the time biosimilars hit the U.S. market (probably in 2023), the company will rely less on Humira. That's not to mention the suite of products AbbVie got its hands on thanks to its May 2020 acquisition of Allergan in a cash-and-stock transaction valued at $63 billion.

Allergan's Botox franchise -- the most important of its product lines -- will help AbbVie keep its revenue growing. Further, AbbVie's pipeline boasts several dozen clinical programs. Something else to consider for income-seeking investors before buying shares of the drugmaker is its dividend yield. AbbVie's current yield of 4.29% compares favorably to the 1.37% yield of the S&P 500 (as of May 31). That, coupled with a reasonable cash payout ratio of 46.5%, make the company look like a dividend investor's dream.

AbbVie has raised its payouts by 128.1% in the past five years, and the pharma company is likely to continue rewarding shareholders in this way for many years to come. 

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2. Amgen

At first glance, biotech giant Amgen may not look like a stock worth buying, especially given its poor financial results during the first quarter. Overall, the company's sales dropped to $5.9 billion, 4% lower than the year-ago period. Many of Amgen's best-selling medicines saw declining sales, including RA drug Enbrel, whose sales dropped by 20% year over year to $924 million. However, investors -- particularly income-seeking ones -- should look past these issues.

For one, the company's top-line problems are due in part to the coronavirus pandemic. The outbreak has affected both patient visits and new diagnoses, according to Amgen. The company is confident that once these headwinds subside, its financial performance will pick up. It is also worth noting that in late May, the U.S. Food and Drug Administration (FDA) approved Amgen's Lumakras, a treatment for advanced or metastatic non-small cell lung cancer (NSCLC).

Lumakras specifically targets NSCLC patients with a mutation of the illness called the KRAS G12C mutation, which occurs in about 13% of those with the disease. Lumakras is the first FDA-approved medicine for NSCLC to target this mutation. Given that lung cancer is one of the most common cancers, there will be a large market for Amgen's newly approved medicine.

Further, much like AbbVie, Amgen has a long list of pipeline programs. The company can count on new approvals every year, which will also help its revenue and earnings growth in the long run. Amgen's dividend yield of 2.8% and its modest cash payout ratio of 38.9% speak to its ability to sustain dividend increases year after year. The company has increased its payouts by 76% in the past five years. Investors looking for solid dividend stocks to buy and hold for a long time would do well to add shares of this biotech stock to their portfolios.

This article represents the opinion of the writer, who may disagree with the “official” recommendation position of a Motley Fool premium advisory service. We’re motley! Questioning an investing thesis -- even one of our own -- helps us all think critically about investing and make decisions that help us become smarter, happier, and richer.