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Big Pharma stocks can be great long-term investing vehicles because of their sizable free cash flows and frequently rich shareholder rewards programs, not to mention the economically insensitive nature of the pharmaceutical business model as a whole. Even so, there are some pharma companies that simply stand apart from the crowd when it comes to creating value for shareholders. 

In my view, the truly elite Big Pharma stocks worth buying right now are Bristol-Myers Squibb (NYSE:BMY), Merck & Co. Inc. (NYSE:MRK), and Pfizer (NYSE:PFE). Here's why. 

Bristol has transformed itself into the immuno-oncology leader
Bristol's stock has been on fire this year because of the breakout regulatory and commercial success of its cancer immunotherapy drug Opdivo. With multiple indications -- such as advanced skin, lung, and kidney cancer -- now in hand, and an extremely rapid market uptake as well, Bristol's new franchise drug was able to generate a staggering $704 million in global sales in the first quarter of 2016.

BMY Chart

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However, Opdivo isn't the entire story behind Bristol's healthy 9% year-over-year rise in first quarter revenue. The drugmaker also reported particularly strong growth of its relatively new hepatitis C product Daklinza, its leukemia drug Sprycel, and its blood thinner Eliquis, which is co-marketed with Pfizer. The long and short of it is that Bristol sports a diverse mix of high growth pharma products that are supporting its breakout performance this year. 

Looking ahead, Bristol is gearing up to launch Opdivo for hard-to-treat classical Hodgkin lymphoma, meaning that there's little reason to believe that its sky high sales trajectory will slow anytime soon. In short, the only major concern surrounding Bristol's top-line at the moment is the longevity of its hep C sales. So, with a dominant and growing position in the red hot immuno-oncology space, and a bevy of other growth products to boot, Bristol is certainly worthy of a deeper dive. 

Merck's growth profile may not be exciting, but the future looks bright
Unlike Opdivo, Merck's rival immunotherapy, Keytruda, hasn't exactly set the world on fire from a sales standpoint. In the first quarter, for instance, Keytruda garnered a more modest $249 million in sales, despite being approved for some of the exact same indications as Opdivo.

The good news is that Merck has launched a monstrous clinical program for Keytruda that could garner several additional high dollar label expansions moving forward. As an added bonus, Merck owns one of the deepest and richest clinical programs for immuno-oncology drugs based on checkpoint inhibition and modulation:

Image source: Merck.

Apart from its growing immuno-oncology footprint, Merck is also aggressively pursuing the massive hep C market via the launch of Zepatier earlier this year. By undercutting the major players in hep C on price, the drugmaker is hoping to convince payers to eventually give Zepatier a favored reimbursement status.

Although this price-based strategy is far from a sure thing given that Zepatier does have some safety issues and its chief competitors could simply lower their prices as well, this new growth product should help Merck stabilize its top-line while its promising immuno-oncology platform continues to mature. 

And if Merck's rich immuno-oncology assets aren't enough to tip the scales for investors, there's always the fact that this Big Pharma sports free cash flows in excess of $12 billion per year, and offers a dividend yield that tops most major drug companies at 3.28% right now. 

Pfizer's innovative products business is taking shape
Pfizer has taken a lot of heat of late for its failure to make a definitive move regarding the future of its legacy products business, which has been weighing on its top-line for some time now. But while the drugmaker has yet to clear the air on this pivotal issue, investors would be unwise to overlook its emerging innovative products business.

Specifically, Pfizer has been generating tremendous growth within this business segment, due largely to its new breast cancer drug Ibrance, the aforementioned blood thinner Eliquis, and the pneumococcal disease vaccine Prevnar 13. Perhaps the best part is that Pfizer is inching closer to regulatory filings for its own immuno-oncology drug avelumab, as well as its novel cholesterol medicine bococizumab. Both of these experimental product candidates have the potential to generate megablockbuster sales figures within a few short years. 

Until Pfizer either breaks apart or gobbles up another drugmaker to shore up its legacy products business, though, I think the main reason to own this particular Big Pharma stock is its noteworthy dividend yield of 3.4%. After all, Pfizer's ample free cash flows, combined with the mountain of cash already on its balance sheet, implies that its better than average dividend payout for a pharma stock should be sustainable for the long-haul. 

Are these 3 Big Pharma stocks worth buying right now?
While there is certainly a case to be made that all of these pharma stocks are fairly, or perhaps over-, valued at the moment, I'd argue that each company offers a tremendous amount of deep value by way of their robust clinical pipelines and recent product launches that's not presently reflected in their respective share prices. And with each stock sporting a reasonable, and most importantly sustainable, dividend yield, investors are essentially being paid to wait for this deeper value to be realized. So, my take is that these top pharma stocks are indeed worth adding to your portfolio right now. 

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.