There is no reason for Clinical Data's (Nasdaq: CLDA) investors to be depressed. After the Food and Drug Administration approved Viibryd, its depression drug, on Friday, shares ran up a whopping 67% on Monday and tacked on an additional 5% today.

The increase is certainly deserved. I guessed an approval was more likely than not, but there was still a lot of uncertainty baked into the stock before the FDA's decision.

In fact, there still is.

Even after the run-up, Clinical Data is only a $750 million company. That's a pretty low value given the huge market for depression drugs. Forest Labs' (NYSE: FRX) Lexapro sold $587 million in just its most recent quarter. Eli Lilly's (NYSE: LLY) Cymbalta rang in at $825 million during the third quarter, although it has the advantage of being also approved for pain indications.

The skepticism that Viibryd can reach those multibillion-dollar levels is completely valid. It'll have to compete with Lexapro and Cymbalta in addition to cheap generic versions of drugs such as Pfizer's (NYSE: PFE) Zoloft and Lilly's Prozac. Those are some lofty names to compete against. Labopharm's (Nasdaq: DDSS) new antidepressant drug Oleptro managed just $0.8 million in sales in its launch quarter; the fourth quarter results should give a better picture, but that's not exactly bolting out of the gate.

Viibryd hasn't been tested against current offerings, so there's little incentive for doctors to try it on any patients besides those that have failed other treatments. The side effects -- including sexual ones seen in other antidepressants -- seem to be mild, but without Viibryd being compared with other drugs, it's hard to know if they're truly milder than what's already out there.

Clinical Data plans to launch Viibryd in three to four months. That is, if it doesn't find a partner or buyer first. Management said it's been in talks with companies, and it'll consider accepting a buyout offer. But keep in mind that putting a "For Sale" sign on the front lawn doesn't necessarily mean a buyer will appear at the right price. Savient Pharmaceuticals (Nasdaq: SVNT) announced its intent to find a buyer, but none appeared.

Clinical Data looks fairly priced to me. Until management can prove that it can grab a solid share of the antidepressant market or find a buyer that thinks it can, I suspect shares will languish at this level.

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Fool contributor Brian Orelli, Ph.D., doesn't own shares of any company mentioned in this article. The Fool has a disclosure policy.