High-yield dividend stocks, on the balance, tend to be more trouble than they're worth. Those high dividends are often the Having said that, there are arguably a handful of rare exceptions such as the big pharma stocks AstraZeneca (AZN 0.22%) and GlaxoSmithKline (GSK -0.24%).

Both of these elite drugmakers have been going through a tough period as the result of the loss of exclusivity for former top-selling medicines. But they now appear primed to enter the next phase of their respective life-cycles within the next few years. As such, Astra and Glaxo could prove to be incredible bargains for investors willing to let this process play out. Here's why. 

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AstraZeneca is emerging from the haze of the patent cliff

The British pharma giant AstraZeneca sports one of the richest dividend yields at 5.58% among all major drug manufacturers. However, the drugmaker's ongoing battle with the patent cliff -- highlighted by the loss of exclusivity for the acid reflux medication Nexium -- has put its dividend at substantial risk moving forward. Astra's 12-month trailing payout ratio of 104%, after all, suggests that its handsome payout may be unsustainable. 

The flip side of the coin, however, is that Astra has stubbornly resisted any changes to its dividend program even during the worst of times. And the company now appears close to emerging from the haze of the patent cliff due to its robust clinical pipeline.

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As a prime example, Astra recently gained an accelerated approval for its PD-L1 checkpoint inhibitor Imfinzi (durvalumab) as a second-line therapy for metastatic urothelial carcinoma, or advanced bladder cancer for short. That's a key milestone because Imfinzi is expected to be a major growth engine for the company moving forward, and perhaps transform into its next flagship medication. Imfinzi's sales, after all, are forecast to reach a hefty $2.3 billion as soon as 2020, according to some analysts.  

Most importantly, Imfinzi's approval gives Astra a full compliment of high-growth cancer drugs following the fairly recent approvals of Tagrisso for mutated EGFR cancers, and Lynparza for ovarian cancer. Taken together, these three new growth products are expected to play a pivotal role in management's stated 2023 goal of transforming Astra into one of the fastest growing pharma companies in the world.

Bottom line: Astra is on the cusp of finally returning to modest top line growth in 2018, and its longer-term growth prospects are improving as well. As such, the company's sky-high dividend yield might ultimately survive the ravages of the patent cliff. 

GlaxoSmithKline is slowly returning to growth

At 4.55%, Glaxo's stately yield is certainly a good reason to considering adding shares to your portfolio. However, this big pharma is also in a state of transition like its peer Astra, and that could translate into a meaningful reduction in its payout going forward.

Long story short, Glaxo is barreling toward the introduction of generics for its top-selling asthma medication Advair in the United States, but it has yet to develop a viable heir-apparent. Instead, the company is currently relying on a growth-by-committee strategy and improving profit margins to offset Advair's slumping sales. 

The encouraging news, though, is that Glaxo's top line is forecast to grow by around 3% next year -- that is, depending on how far Advair's sales slip, and presuming a successful introduction of the drugmaker's highly anticipated shingles vaccine Shingrix . That's a respectable uptick after a tough couple of years, and suggests that Glaxo is definitely in turnaround mode under its new CEO Emma Walmsley.

Now, the sustainability of Glaxo's juicy yield is definitely a big question mark at this stage, especially with its 12-month trailing payout ratio at a sky-high 232%. The drugmaker's next major wave of pharma products that may harbor a true franchise-level drug, after all, remain three to perhaps four years away from coming online.

So Glaxo's modest near-term growth prospects might not be enough to stave off a reduction to its dividend -- especially with Walmsley eyeing a possible shift in the drugmaker's capital allocation strategy in order to speed up the turnaround process. But Glaxo does come across as a company in full rebound mode based upon its improving fundamentals and dynamic new leadership.  

Investing takeaways

High-yield dividend stocks almost always have some kind of major drawback that makes them unappealing long-term investing vehicles. Astra and Glaxo, though, appear to be reasonably close to putting their troubles in the rear view mirror, and returning to land of the living, so to speak.

For instance, Astra has worked diligently toward becoming a major player in the high-growth oncology drug space. The net result is that the drugmaker's annual revenue is forecast to more than double from current levels by 2023 -- at least according to Astra's internal projections. 

Glaxo, for its part, has yet to release anything resembling a long-term guidance because of the uncertainties surrounding Advair, its clinical pipeline, as well as its use of capital going forward. That said, the drugmaker has done a nice job of increasing its profitability and boosting growth across its core businesses over the past year. And with a bevy of clinical studies underway and a new CEO in place, the storm clouds appear to finally be dissipating.