Healthcare stocks are in the the midst of a historic run, fueled by wider access to medical services around the globe and a surge in new drug approvals over the past few years in the United States. Consequently, there aren't a whole lot of healthcare stocks that qualify as "cheap" these days.

Having said that, Amarin Corp. (NASDAQ:AMRN), Horizon Pharma plc (NASDAQ:HZNP), and Valeant Pharmaceuticals International (NYSE:VRX) all still sport fairly attractive valuations -- at least on paper. So let's dig deeper to consider to see if these comparatively cheap healthcare stocks are worth buying right now. 

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Amarin is a cheap biotech with an appealing risk profile

Irish biopharma Amarin has been trading at a fraction of the commercial potential of its prescription fish-oil pill, Vascepa, for awhile now, and the reason isn't exactly a secret. As Vascepa closes in on a top-line readout for its cardiovascular outcomes trial either late this year or early in 2018, the company's stock has started to attract an increasing number of short-sellers:

AMRN Short Interest Chart

AMRN Short Interest data by YCharts

The fundamental reason is that recent clinical studies have cast doubt on the long-term cardiovascular benefits of fish oil supplementation, especially among patients already taking statins.  

While there's no guarantee that Vascepa will prove to be a major advancement in the prevention of cardiovascular events as an add-on to statin therapy, there is reason to believe that this drug's sales won't utterly collapse the trial does go belly up. 

A recent science advisory from the American Heart Association (AHA), for instance, recommended fish oil supplementation at least for patients with prevalent heart failure based on all available evidence to date. Although the AHA couldn't recommend broader use of Omega-3 therapies in light of the mixed bag of results so far, there is enough scientific evidence in play to suggest that these drugs will have an important role to play in the battle against heart disease. 

What this advisory may mean for Amarin is that Vascepa's sales might not fall all that much from current levels. Vascepa, after all, is currently being sold mainly to patients with extremely to modestly high triglyceride levels -- not across the entire spectrum of patients at risk for cardiovascular disease.

The flip side of the coin is that if the trial does show a cardiovascular benefit for Vascepa as an add-on to statin therapy, this stock could scream higher based on the drug's projected $2 billion-plus commercial opportunity. So if you're on the hunt for a cheap healthcare stock with an attractive risk-to-reward ratio, Amarin is definitely worth checking out. 

Horizon's turnaround story hasn't convinced short-sellers

Horizon is another healthcare stock that's cheap at least partly because of the influence of short-sellers. The drugmaker, after all, sported a fairly substantial short ratio of 8.45% at last count. 

Short-sellers have piled into this stock because payers have balked at covering some of the drugmaker's high-priced specialty medicines, such as Duexis and Vimovo. As a result, Horizon was forced to markedly lower its 2017 outlook earlier this year.

The odd part, though, is that Horizon's top line is still forecast to grow by a healthy 8.1% next year, thanks to its rapidly growing orphan drug franchise. Horizon's shares are thus trading at less than twice the company's projected 2018 revenues, which is about as cheap as it comes in the pharma space.

Why is Horizon worthy of consideration? The headwinds surrounding high-priced specialty medicines are undoubtedly real, but Horizon is arguably being thrashed to the extreme, especially in light of its demonstrated pivot to orphan drugs. The company, after all, sports six orphan drugs, and 65% of its revenue now comes from the ultra-high-growth rare-disease arena as a result.

And with its recent acquisition of River Vision Development Corp. for its late-stage biologic, teprotumumab, indicated for moderate to severe thyroid eye disease, Horizon's less controversial orphan drug portfolio should continue to play a bigger and bigger role in its valuation.  

Now, Horizon's specialty medicine portfolio might stumble again, as payers appear set to do everything they can to steer patients away from Duexis and Vimovo. But this stock is arguably still too cheap to ignore based on the company's emerging orphan drug footprint.   

Valeant's stock is on the mend, but can it keep up the momentum?

Valeant's stock is trading at a price-to-sales ratio of 0.6. That's not a typo. The unfortunate part is that this fire-sale valuation might actually be warranted.

Long story short, Valeant's shares collapsed after the company got its hand caught in the mousetrap that is the drug-pricing controversy. Valeant's core business model, after all, has been to acquire drugs already on the market, reprice them at jaw-dropping amounts, and subsequently relaunch them. When the company drew flak from payers and Congress for this questionable practice, Valeant imploded because it also took on a mountain of debt to employ this rather aggressive growth-by-acquisition strategy.  

Valeant is struggling to answer a key question about its future: How will it solve its debt problem and return to growth at the same time? Over the past year, the drugmaker has been divesting assets such as the advanced prostate cancer therapy Provenge and attempting to pay down debt at the same time to allay investors' fears about this overarching issue.

However, these efforts haven't changed the company's fundamental outlook. Valeant, after all, still owes a whopping $28 billion, and its interest expense is moving in the wrong direction -- despite an overall lower debt load.

So while the drugmaker's shares have been rallying of late -- gaining 29% in the past week alone -- because of news that hedge-fund manager John Paulson has joined the board, Valeant's long-term value proposition remains a mystery for the most part. In fact, the company could end up divesting multiple core assets to put its debt problems to bed once and for all -- but such a move would also alter its underlying growth prospects.

All told, Valeant is cheap, but this picture may change dramatically as its asset divestiture plans continue to unfold. So this beaten-down healthcare stock is arguably a buy only for investors with a strong appetite for risk. 

George Budwell has no position in any stocks mentioned. The Motley Fool owns shares of and recommends Valeant Pharmaceuticals. The Motley Fool has a disclosure policy.