A well-rounded investment portfolio should arguably always include a couple of Big Pharma stocks. These companies, after all, sport some of the highest profit margins and steady free cash flows, and they often reward shareholder richly.

With this in mind, I think investors may want to consider adding Johnson & Johnson (NYSE:JNJ), Merck & Co. (NYSE:MRK), and Pfizer (NYSE:PFE) to their portfolios right now. Here's why.  

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J&J is a solid stock to anchor any portfolio

Perhaps I'm biased, but I think J&J belongs in every portfolio. After all, this diversified healthcare company is a dividend aristocrat and sports a triple A-rated balance sheet. As an added incentive to own this stock, J&J is one of the few drugmakers that has been largely unfazed by the loss of exclusivity for top selling medicines such as its blockbuster arthritis drug Remicade. 

By investing an abnormally high percentage of its total sales on R&D (about 13% in 2015), J&J has been able to get in front of patent losses by bringing innovative new medicines to market in record time and expanding the labels of already approved products to drive higher sales volumes.

As a prime example, the drugmaker is forecasting $3 billion worth of label expansions for key products like the cancer drug Imbruvica and the HIV medicine Edurant over the next two to three years. And that's not even delving into its robust pipeline of novel clinical candidates that could produce several megablockbuster drugs in the next decade.  

The bottom line is that J&J is the top Big Pharma company when it comes to the strength of its balance sheet, dividend history, and innovation.

Merck's fortunes are finally turning around 

Merck's new flagship cancer drug Keytruda appears set to potentially leapfrog Bristol-Myers Squibb's (NYSE:BMY) Opdivo next year as the undisputed king of the high-growth cancer immunotherapy market.

The short story is that Keytruda got the green light from the FDA this year as a frontline treatment for metastatic non-small-cell lung cancer (NSCLC) in patients with high PD-L1 expression. Opdivo, on the other hand, missed its primary endpoint in a late-stage trial for this high-value indication.

The heart of the matter is that this pivotal approval is expected to add at least a billion in sales to Keytruda's annual haul next year and help it erode Opdivo's market share in later-line settings for NSCLC. 

Because Merck is dealing with the upcoming loss of exclusivity of core medicines like Remicade, Cubicin, and Zetia, the drugmaker's top line won't necessarily feel the full impact of Keytruda's astonishing growth right away. Even so, Merck is still forecast to post a respectable compound annual growth rate for its top line in excess of 6% over the next five years, thanks largely to Keytruda. 

Perhaps the key takeaway is that Keytruda's breakthrough in NSCLC over its chief rival Opdivo should give the drugmaker a much-needed cushion to continue building out its pipeline organically. In other words, Merck shouldn't have to resort to paying a hefty premium to acquire a revenue-generating peer simply to offset the anticipated dip in sales from drugs like Remicade and risk cutting its dividend program in the process. 

Pfizer offers an extremely deep pipeline and an under-appreciated balance sheet

Pfizer's stock is arguably worth owning just for its superb dividend yield of 3.9%. However, the drugmaker also sports a late-stage clinical pipeline of 41 drug candidates that are currently in either pivotal trials or in the registration phase of their development. 

How did Pfizer build such a rich late-stage pipeline? The basic answer is money. Given the drugmaker's free cash flows of $14.6 billion over the past year, Pfizer hasn't been shy about jettisoning early stage compounds that lack strong safety profiles, at least some early efficacy signal, and a clear ability to carve out a profitable niche. The company's enormous cash position of over $14 billion has also enabled its R&D team to invest heavily in licensing deals and acquisitions to bolster its clinical pipeline over the last few years. 

The exciting part is that Trump's proposed corporate tax reforms could provide Pfizer with even more firepower to boost its R&D engine moving forward. Digging into the details, Pfizer's CEO Ian Read mentioned at the Guggenheim 4th Annual Boston Healthcare Conference this week that the company would be interested in pursuing additional acquisitions if U.S. tax reforms become reality. 

All in all, Pfizer appears well on its way to overcoming the challenges presented by the patent cliff in the past few years, making it worth a deeper dive right now. 

George Budwell owns shares of Pfizer. The Motley Fool recommends Johnson and Johnson. Try any of our Foolish newsletter services free for 30 days. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.