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If you're interested in investing in pharmaceutical stocks, you're not alone. The potential to profit from aging baby boomers, an increasingly insured population, and innovative therapies has made drugmakers some of the market's top performers.

However, investing in pharmaceutical stocks does come with risk. Pharmaceutical companies are continuously plowing money back into their research pipelines and there's no guarantee that spending will produce future winners. That means drugmakers can struggle to offset the market share lost to generic competitors when patents on existing drugs expire. Given that backdrop, let's consider three top pharmaceutical stocks investors should be tracking and learn a bit more about how these companies hope to increase their sales and profit going forward.

No. 1: Johnson & Johnson (NYSE:JNJ)
Johnson & Johnson is a global powerhouse with a product lineup that includes consumer goods products such as Band-Aid, pharmaceuticals including the top-selling Remicade, and medical devices such as insulin pumps.

Last year, those products combined to generate over $74 billion in sales and adjusted earnings per share of $5.97.

The company's sheer size warrants attention, but investors should focus on its pharmaceuticals segment, which is J&J's largest business. The company markets a variety of medicine used to treat autoimmune disease, cardiovascular disease, and cancer, and its top-selling drugs are always battling competitors for market share.

Remicade, a therapy for rheumatoid arthritis that had global sales of $1.6 billion in the first quarter and accounts for 9% of J&Js total sales, is the company's best-selling drug. But Remicade has lost patent protection in some European markets, which is weighing down sales as biosimilars launch in those countries, and pressure could build as Remicade patents expire in other markets, including the U.S. in 2018.

In the short term, slowing sales of Remicade in Europe are being blunted by fast-growing drugs such as the psoriasis treatment Stelara. Stelara's sales topped $500 million last quarter, and future sales could strengthen following the high-profile failure of a potential competing therapy that could have hit the market in 2016. Also providing sales growth are J&J's Xarelto, a disruptive new anticoagulant, and Invokana, which is part of a new class of diabetes medicine.

Because J&J has a stable of top-sellers and a host of drugs making their way through trials, and because it's among the most diversified of the big pharmaceuticals, investors should be watching the company closely.

No. 2: Pfizer (NYSE:PFE)
With sales of more than $40 billion a year stemming from a slate of top-selling medicines, Pfizer is another industry Goliath. 

However, Pfizer's top line has suffered much more than J&J's over the past few years following the loss of patent protection on cholesterol buster Lipitor, which was once the planet's top-selling medicine. Overcoming lost Lipitor sales has proven incredibly tough, and the company's revenue has slipped from more than $65 billion to below $50 billion since its patent expired.

But better times could lie ahead. The drop-off in Lipitor sales is stabilizing, and new products and programs could return Pfizer to revenue growth soon.

Pfizer is relying on its Prevnar family of vaccines, along with Xalkori, Xeljanz, and the newly-launched Ibrance, to help it turn the corner. Future sales growth could also develop from the company's pipeline of drugs targeting autoimmune disease, high cholesterol, and cancer.

Along with tracking the performance of those treatments, investors should keep an eye on how Pfizer's acquisition of pharma peer Hospira pans out. The deal would catapult Pfizer into a leadership position in the burgeoning biosimilars market, which could be worth billions of dollars annually given that $100 billion in biologics are due to lose patent protection over the next five years.

No. 3: Bristol Myers Squibb Co. (NYSE:BMY)
Bristol-Myers Squibb has always been among the leaders in this industry. Like J&J and Pfizer, it is working hard to blunt patent risk by rolling out innovative new treatments.

Bristol-Myers Squibb is investing heavily in biologics that can complement its traditional small-molecule drug business. Some intriguing fast-growing therapies include the anticoagulant Eliquis, cancer drug Yervoy, and PD-1 inhibitor Opdivo.

In the first quarter, Bristol-Myers Squibb reported that sales grew 6% to $4 billion; however, removing the impact of divesting its diabetes business and adjusting for currency impacts, Bristol-Myers Squibb's operational sales growth was up 17%. That growth came from Eliquis sales jumping from $106 million to $355 million, Yervoy sales climbing from $271 million to $325 million, and the newly-launched Opdivo racking up sales of $40 million in the quarter.

What makes Bristol-Myers Squibb a key Big Pharma stock to watch from here, though, is the potential for label expansion to enable Yervoy and Opdivo to be used for more patients. If the company can execute on its label expansion strategy, both drugs could generate far greater revenue for the company down the road.

Tying it together
Pharmaceutical stocks are intriguing, but the industry does face risks associated with pipeline failure and patent expiration that shouldn't be ignored, particularly by dividend investors relying on stable growth to fuel those payouts.

Although those risks are real, J&J, Pfizer, and Bristol-Myers Squibb are gold standards with significant profit-boosting potential. Investors looking to invest in pharmaceuticals stocks might be best served concentrating their attention on these three.