Pharmaceutical stocks are generally an outstanding place to look for sustainable sources of passive income. Even though most companies offer fairly modest yields due to the costly nature of developing new drugs, there are a handful of big pharma stocks that do sport surprisingly high yields.

With this theme in mind, we asked three Motley Fool investors which high-yield pharma stocks might be worth buying right now. They recommended GlaxoSmithKline (NYSE:GSK), Pfizer (NYSE:PFE), and Johnson & Johnson (NYSE:JNJ).

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Risky but appealing

George Budwell (GlaxoSmithKline): With a dividend yield of 4.86%, the British pharma GlaxoSmithKline easily offers one of the richest payouts within the big pharma landscape. To be honest, though, Glaxo's sky-high dividend has long been one of the only reasons to buy its stock. The dark days of high-profile clinical failures, costly bribery cases, and poor capital allocation have weighed heavily on its shares in the past few years.

Glaxo's new management team, however, has laid out a comprehensive plan to change this dire outlook. New CEO Emma Walmsley -- the previous head of Glaxo's consumer healthcare business -- unveiled the company's leaner, more focused business plan last July. The key points are that Glaxo plans to improve gross margin across its three businesses (vaccines, pharma, and consumer healthcare), cut development timelines for new products, and reduce pharma R&D costs significantly by slashing the overall number of ongoing trials.

Fortunately for income investors, Glaxo has decided to forgo a dividend reduction for the time being while these cost-saving measures play out, even though the company's enormous trailing payout ratio of 200% suggests that a suspension or a sizable reduction would be wise. After 2018, though, management does plan to directly tie the dividend payout to cash flow generation, which may or may not result in a reduction, depending on how newer products like its highly anticipated shingles vaccine, Shingrix, perform in the interim.   

All told, Walmsley's vision for the future appears to have the company back on solid ground. As such, this risky high-yield stock might be worth checking out right now.  

This is arguably big pharma's most rock-solid dividend 

Sean Williams (Pfizer): High-yield dividend stocks are hard to come by in the healthcare sector, but big pharma is home to quite a few solid income stocks. Among those, Pfizer and its 3.5% yield looks incredibly attractive.

Pfizer has obvious advantages over most drug companies because of its sheer size. It has a successful and highly profitable mature drug portfolio, as well as a slew of newer therapies that it's brought to market. Additionally, as of Aug. 1, 2017, it had 99 clinical-stage or registration-stage programs. Even with the odds against drugmakers succeeding, having practically 100 novel and/or label expansion studies ongoing should give Pfizer plenty of opportunities to further expand its portfolio.

In recent years, Pfizer has really benefited from its focus on specialty medicines. Specialty indications, such as oncology, have really driven sales and profitability higher given rapid organic demand growth and strong pricing power. Sales of Ibrance, the company's leading advanced breast cancer drug, have grown by 63% through June, and are on track to top $3 billion this year. Other strengths include oral anticoagulant Eliquis, pneumococcal vaccine Prevnar 13, and anti-inflammatory Xeljanz.

Income investors also can't overlook the main reason to buy into big pharma: inelasticity. Though recessions and stock market corrections are perfectly normal, people don't stop getting sick just because stock prices fall or the economy contracts. This creates a fairly steady and growing patient pool for Pfizer to rely on.

Bigger isn't necessarily better when it comes to investing, but if you want a solid high-yield pharmaceutical stock, Pfizer could be a great choice.

This steady Eddie is poised for growth

Brian Feroldi (Johnson & Johnson): With a yield of just 2.5%, Johnson & Johnson isn't the highest-yielding stock on this list. However, the company's puny yield is largely a result of rapid share price appreciation. Long-term investors have enjoyed market-beating total returns over the last one, three, five, and 10 years. With a solid business model in place and growth opportunities about, I think investors can expect more of the same moving forward.

Johnson & Johnson's third-quarter results demonstrate why my bullishness is warranted. The company's pharmaceutical division just posted sales growth of 15.4%, thanks in large part to the acquisition of Actelion. The company's two other divisions -- medical devices and consumer products -- also posted respectable growth of 7% and 2.9%, respectively, which is quite decent given Johnson & Johnson's size. Add it all up and the company treated investors to 10% growth in revenue and 13% growth in EPS.

Looking ahead, Wall Street expects Johnson & Johnson to produce EPS growth in excess of 6% annually over the next five years largely on the back of growing pharmaceutical sales, margin improvements, and steady share buybacks. Given Johnson & Johnson's long history of success and deep pipeline, I think Wall Street's estimates might even be conservative. If true, then the company should have no problems continuing its 54-year streak of consecutive dividend increases.

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.