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Not everything about Big Pharma is big. Some stocks of the largest drugmakers in the world actually trade at relatively low valuations. Here's why Mallinckrodt (NYSE:MNK), Bayer AG (OTC:BAYR.Y), and Bristol-Myers Squibb (NYSE:BMY) look to be three of the most incredibly cheap Big Pharma stocks around.

Generic drugs and pig glands

Andrew Johnson was the U.S. president when Mallinckrodt was founded back in 1867, though it's naturally a much different company now. Most of Mallinckrodt's success in its recent history stems from generics and Acthar, a brand drug made from pig pituitary glands.

In 2015, Mallinckrodt made $3.35 billion in net sales. Roughly 37% of that total stemmed from the company's specialty generics business. Specialty generic drugs sold by Mallinckrodt include hydrocodone, oxycodone, and methylphenidate extended-release tablets. 

Mallinckrodt's biggest winner, however, is its specialty branded drug Acthar. The drug is approved to treat several indications, including multiple sclerosis, infantile spasms, and lupus. Acthar generated sales of over $1 billion in fiscal year 2015, representing nearly 31% of the company's total revenue.

A couple of other specialty branded products are also important for Mallinckrodt. Inomax, a nitric oxide inhalation vasodilator that helps treat breathing problems in babies, has become the company's second-biggest product. Pain reliever Ofirmev, an intravenous form of acetominophen, also kicks in significant sales -- it notched $263 million in fiscal 2015.

Mallinckrodt trades at eight times forward earnings. Investors would be hard-pressed to find a Big Pharma stock with a more attractive valuation.     

No headaches with this stock

Mallinckrodt has been around a long time, but Bayer was founded even earlier: The German company started operations in 1863.

Bayer is probably best known for Aspirin and still sells the pain reliever. Nearly 120 years after its launch, Aspirin remains the top-selling product in Bayer's consumer health business segment. Another popular pain reliever, Aleve, is the company's second-biggest product for the business unit.

The company's pharmaceuticals segment generates the most money for Bayer. The biggest product for the pharmaceuticals business unit is blood thinner Xarelto. Johnson & Johnson markets the drug in the U.S., while Bayer sells Xarelto elsewhere.  

Partnerships have been a key to Bayer's success. The company's relationship with Regeneron has worked out especially well. Age-related macular degeneration drug Eylea was the first drug launched by the two partners. Bayer is also teaming up with Regeneron on other eye disease drugs.

Bayer's forward price-to-earnings multiple currently stands just over 11. That makes this stock a bargain.

Dividends and growth on the way

Some investors place a higher priority on dividend yield. Others prefer stocks with tremendous growth potential. With Bristol-Myers Squibb, investors can have both.

Bristol has been one of the best Big Pharma dividend stocks for two decades. Its dividend yield currently stands at 3.07%.

What might surprise you, though, is that Bristol-Myers Squibb appears to be set for some pretty impressive growth. The consensus among Wall Street analysts is that the pharmaceutical company will grow earnings at an annual rate of more than 19% over the next five years. How can Bristol pull off that kind of growth? Sales for cancer drug Opdivo are soaring. The same is true for anticoagulant Eliquis. Bristol also can count on solid performance from another cancer drug, Sprycel, and from rheumatoid arthritis drug Orencia.

At first glance, the company's pipeline might not look all that great. Bristol has only one late-stage candidate, prostate cancer vaccine Prostvac. If Prostvac is approved, though, analysts think it could reach peak annual sales of $1.3 billion. Bristol also claims a dozen phase 2 clinical studies and 17 phase 1 studies in its pipeline. There's definitely more risk with a pipeline loaded with mid-stage and early-stage candidates, but with a little luck, Bristol could have several new winners in its product lineup down the road.

The stock trades at 16 times forward earnings. That's not bad when compared to the broader industry. However, when you factor in Bristol's earnings growth potential and commitment to paying strong dividends, this Big Pharma stock looks inexpensive.

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.