Stocks have had a great year in 2013, and the market's biggest names haven't been slowed down a bit as the Dow Jones Industrial Average (INDEX: ^DJI) has soared to 18% year-to-date gains. But not all of the Dow's blue chip components have been equal this year. Take big pharma household name Merck (NYSE: MRK): While Merck's beaten the Dow and had a great year, this stock's fallen into the bottom half of the index among year-to-date performers, and trails some of its biggest health-care rivals in 2013. What's gone right (and wrong) for Merck this year? Let's take a look back at 12 months of progress for one of the biggest names in the health-care business.

The patent cliff's huge hit
It's safe to say that Merck has struggled with the patent cliff this year, but it's been a big problem across all of big pharma. Merck's chief rival and fellow Dow member Pfizer (NYSE: PFE) has seen its sales slide behind falling revenue from cholesterol-fighting drug Lipitor. Pfizer's former top seller lost patent protection last year, and has seen revenue plunge 49% year-over-year through 2013's first months.

Same story at Merck, although the company's big patent-cliff loss, Singulair, has suffered a much bigger blow. Singulair, a treatment for asthma and respiratory illnesses, has seen its sales drop off by 74% year over year through the first nine months of 2013 -- a loss of more than $2 billion in revenue.

Meanwhile, stagnating growth from some of Merck's more promising drugs have led to Singulair's blows being felt with extra vigor. Diabetes duo Januvia and Janumet are this company's stars for the next several years, but they haven't performed that way for Merck in 2013. Januvia, already the recipient of more than $2.8 billion in sales through the first nine months of the year, has seen its sales slip slightly over that period of time. Januvia and Janumet still have room to run, but sliding revenue wasn't what Merck had in mind for its top diabetes drugs heading into this year.

Shaking up development
If Januvia's sluggishness hasn't been bad enough, Merck has taken hits in its pipeline, as well. The biggest news from Merck's R&D division in 2013 came all the way back in February, when the company announced that it would delay the FDA filing of promising bone treatment odanacatib until 2014. That unnerved many investors, despite the promise odanacatib still offers. Many analysts peg the compound, if approved, at peak sales of more than $1 billion, and odanacatib's chances of passing the FDA look very good.

However, Merck's lackluster pipeline drew more and more criticism as the year went on. It's for much more than just the odanacatib misfire, too. Merck spends more on its R&D as a portion of sales than some of its competitors, and for less results. In 2012, for instance, Merck spent 17.2% of its total revenue on research and development. That was a far greater sum than rival Pfizer, which spent only 13.3% of its total revenue on R&D -- and Pfizer's pipeline is one of the best in the business.

The good news going forward is that investors forced Merck's hand in October. The company announced job cuts and savings, and half of the latter will come from R&D. Overall, the plan's expected to save Merck around $2.5 billion annually by 2015. That's desperately needed for this firm, as Merck looks to counter the effects of Singulair's loss, and further upcoming patent expirations in coming years.

A year stuck in neutral
Merck's stock might have done well overall for investors in 2013, but it's been an up-and-down year for the company. Odanacatib's filing delay was more of a nuiscance than real trouble, but Januvia's slowdown, and Singulair's colossal patent-cliff-related hit, have taken a toll on Merck's financials. While the company's savings and cost-cutting plan should help into the future, Merck needs to light a fire under its R&D division to find its next great drugs -- all while keeping its current crop of products on the market selling at peak performance.

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Fool contributor Dan Carroll has no position in any stocks mentioned. The Motley Fool has no position in any of the stocks mentioned. 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.