Stocks are in a precarious place at the moment. Most U.S. companies are no longer trading on anything close to their underlying fundamentals, but rather on pure speculation about what may unfold over the next 12 to 24 months. While a viable COVID-19 vaccine, or perhaps a convalescent plasma therapy, could emerge in record time, there's also the chance that an effective pharmaceutical intervention may take years to develop. There's no way to know for sure -- a fact that simply isn't reflected in the hefty valuations of many U.S. stocks right now. 

The point is that now is probably as good a time as ever to play it safe with your portfolio. And top pharma stocks -- especially those that pay a top-notch dividend -- are arguably one of the best ways to defend against uncertain times. Pharmaceutical companies, after all, generally sell a suite of life-saving products that are largely immune to economic downturns. 

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Which pharma companies should investors consider adding to their portfolio in June? Bristol Myers Squibb (NYSE:BMY) and Pfizer (NYSE:PFE) stand out as two of the best buys in the pharmaceutical space this month. Here's why.  

Bristol: The full package

Not many large-cap companies sport high-single-digit top-line growth, a respectable dividend yield, and an exceptionally strong long-term outlook. That's what makes Bristol so unique within its big pharma peer group.

Following its game-changing acquisition of Celgene last year, the drugmaker's product portfolio is now home to a whopping seven blockbuster medicines: Eliquis, Opdivo, Orencia, Pomalyst/Imnovid, Revlimid, Sprycel, and Yervoy. This suite of growth products, combined with other newly launched medicines such as the blood disorder therapy Reblozyl, are forecast to boost the company's annual revenue by a healthy 8.4% in 2021.

What's more, Bristol's clinical pipeline is easily one of the best in the industry in terms of both productivity and overall depth. The company recently scored major regulatory wins for the closely watched multiple sclerosis drug Zeposia, along with Opdivo's long-sought label expansion, as part of a combo therapy for first-line lung cancer.

Going forward, the biopharma also expects to eventually break into the anti-cancer cell therapy market with product candidates such as ide-cel. Bristol, in short, is well positioned for a lengthy period of solid revenue growth as a result of its stellar clinical pipeline. 

On the dividend side on the equation, Bristol offers investors an annualized yield of just about 3% at current levels. While that's slightly below average for a big pharma stock, Bristol should have little trouble boosting its dividend in the years to come. That's a big plus in an environment where many companies are considering dividend suspensions or reductions. 

All told, Bristol's stock should deliver outstanding returns for investors seeking a safe haven in this turbulent market.   

Pfizer: An outstanding value play

Pfizer's shares have fallen by a noteworthy 8% so far in 2020, thanks largely to its late-stage miss for Ibrance in early breast cancer last month. Investor disappointment at this negative trial result is certainly understandable. Ibrance's entrance into the realm of early breast cancer, after all, may have been worth as much as $8 billion in annual sales.

Pfizer's hefty swoon in response to this high-profile clinical failure, though, might represent an outstanding buying opportunity for value-oriented investors. Pfizer's shares are now trading at a dirt cheap 12.8 times earnings. What's more, the drugmaker also offers a massive 4.22% dividend yield. That's an extremely attractive package for a big pharma stock by any measure.  

Topping it off, Pfizer's clinical pipeline has been one of the most productive in the industry over the last few years. Pfizer racked up a whopping 10 regulatory approvals in 2019 alone, highlighted by the U.S. approval for the ground-breaking heart medicine Vyndaqel.

So while Ibrance's miss in early breast cancer is indeed costly in terms of future revenue, Pfizer shouldn't necessarily be punished -- at least not so severely -- for a fairly rare clinical misstep. The drugmaker is a proven innovator across multiple therapeutic areas. Moreover, Pfizer has been aggressively augmenting its clinical pipeline through several bolt-on acquisitions and partnerships leading into the planned spin-off of the legacy product unit Upjohn with Mylan later this year.  

Bottom line: Pfizer's stock is arguably way too cheap following this latest downturn -- especially for a company with a top-notch pipeline, the financial flexibility to acquire assets on an as-needed basis, and an above-average shareholder rewards program.  

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.