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Pharmaceutical and biotech companies pride themselves on developing treatments with blockbuster potential, and the most successful drugs can bring in tens of billions of dollars in revenue over time. Yet sometimes, companies turn out to have been completely wrong about the prospects for a particular treatment. We asked three of The Motley Fool's healthcare contributors to talk about their experience with failed drugs and which ones were the most disappointing launches they've ever seen. Read about their stories and see if you agree or would choose others instead.

Todd Campbell: I suppose anything can still happen, but the launch of MannKind's (MNKD 5.14%) inhalable insulin Afrezza has to go down as one of biopharma's biggest disappointments of all time.

Afrezza's inhaled, rather than injected, dosing was supposed to catch on like wildfire, but with just 1 million euros in first-quarter sales and 2 million euros in second-quarter sales, there's little for investors to write home about.

Perhaps, Afrezza's lackluster demand stems from worries over lung safety and necessary lung tests, or perhaps it's simply because injections "work" just fine for the vast majority of patients.

Either way, the inability for marketing partner Sanofi (SNY 0.77%) -- one of the globe's most successful diabetes makers -- to spark demand is about as disheartening as it gets for MannKind's investors. Granted, there's still time for Afrezza to catch on, but given that Sanofi can walk away from its licensing deal with MannKind as early as next year, that time is limited.

Cheryl Swanson: Disappointing returns from ridiculously priced drugs have been the theme of far too many cancer treatments over the years. And no cancer drug is as worthless as six-figure priced Zaltrap from French pharma giant Sanofi.

The French don't call you idiotic; they call you dumb as a broom. (Être con comme un balai.) That's not a bad description of Sanofi, when they slapped an $11,000-per-month price ($132,000 yearly) on Zaltrap, despite the drug extending median survival by only 42 days. The drug somehow scraped through the FDA approval process, despite being no better than a slew of other available treatments for metastatic colon cancer such as Roche's Avastin, that cost half as much.

A trio of doctors from Memorial Sloan Kettering put the nail in Zaltrap's coffin. The doctors wrote a blistering op-ed for The New York Times, declaring Sloan Kettering was taking Zaltrap off the institution's formulary. In response, Sanofi cut Zaltrap's price in half. Analysts expect peak sales for Zaltrap never to surpass $400 million.

In the editorial, the Sloan Kettering doctors encouraged their peers to start taking similar actions to address runaway cancer drug prices. With a flood of freakishly expensive new oncology drugs either on the market or headed that direction, we shouldn't have long to wait to see how that plays out.

Dan Caplinger: Two of the most disappointing drug launches of all time came in close succession, as competing companies raced to get their anti-obesity drugs into a market that had lain dormant for more than a decade. For years, VIVUS and Arena Pharmaceuticals (ARNA) looked to gain approval for their respective weight-control drugs, Qsymia and Belviq. Yet when Qsymia was first to get approval in mid-2012, it ran into several problems, including a lack of a marketing partner, slow adoption by insurance companies for reimbursement, and a less favorable safety profile than other anti-obesity prospects. Belviq was approved shortly after Qsymia, but its commercial release ended up getting delayed by a year because of the Drug Enforcement Agency. Belviq also faced similar insurance-related issues.

Years later, sales of the two drugs have been a huge letdown. Based on quarterly results from earlier this year, annual run rates for both drugs are roughly $50 million each, far short of the billion-dollar potential that many analysts foresaw for the anti-obesity industry. Moreover, additional competition is coming not just from other companies making similar drugs but also from entirely different angles. In particular, a drug that targets production of fatty acid molecules and a device that could target the nerve that regulates the digestive system might end up being long-term winners in the space. It's too early to be certain, but for now, both Belviq and Qsymia rank among the most disappointing drug launches in the industry.