MannKind (Nasdaq: MNKD) is scheduled to get a late present from the Food and Drug Administration on or before Dec. 29, when the agency decides whether to approve its inhaled insulin product, Afrezza. But the contents of the package -- an approval or a lump of coal -- remain to be seen.

Or perhaps I should say another lump of coal. The FDA already turned down the marketing application for Afrezza once. Before approving the drug, the agency wanted "data that support the clinical utility of Afrezza."

Has MannKind given the FDA what it needs to approve the drug? It's impossible for you or me to know, since we're not privy to the regulatory conversations. Clearly, management thinks so, but then it did the first time, too.

The bigger problem is that even if MannKind has fulfilled all the requirements, there's no guarantee of an approval. The FDA has had six more months to come up with a new issue to worry about. Perhaps the drug's lung cancer potential? A safety analysis of Pfizer's (NYSE: PFE) inhaled insulin, Exubera, showed a higher incidence of lung cancer among those patients taking the drug than in the study's control group.

And the FDA asking for another safety trial "just to be sure" isn't out of the question. Amylin Pharmaceuticals (Nasdaq: AMLN) and Eli Lilly (NYSE: LLY) know about that all too well, having been sent back to do more experiments on their diabetes drug Bydureon, a long-acting version of Byetta.

What investors need to remember is that neither Bydureon nor Afrezza are miracle drugs. Both have alternatives available: Byetta for Bydureon, and injected insulin for Afrezza. They're certainly more convenient, but the FDA is less concerned with the number of needle sticks and more concerned with making sure there aren't any problems with the new mode of delivery.

While I find it difficult to figure out whether the FDA will approve Afrezza, I can't fault investors for owning MannKind going into the FDA decision. The drugmaker has a market cap of only $1 billion and is clearly worth more if Afrezza is on the market -- and a heck of a lot more if MannKind can turn it into a blockbuster.

We can argue the merits of that last point at a later date -- like if it gets approved next week. For now, just take our Foolish poll then leave a comment lower on the page.

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Fool contributor Brian Orelli, Ph.D., doesn't own shares of any company mentioned in this article. Pfizer is a Motley Fool Inside Value recommendation. 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 Fool has a disclosure policy.