It's the binary news events -- clinical trial results and Food and Drug Administration approvals -- that make drug developers so fun to invest in, and so hard to stomach ... sometimes at the same time.

The FDA decision calendar is a little light this month, but there are still a few companies hoping for a heart-shaped "approved" letter in their mail box.

Medicine for more
Johnson & Johnson's (NYSE:JNJ) Risperdal Consta is already approved, but this month the company should have an opportunity to expand sales of the antipsychotic. The long-lasting version of Risperdal, which was developed using technology from Alkermes (NASDAQ:ALKS), is being reviewed as a treatment for frequently relapsing bipolar disorder.

Patients in this subset make up only 10% to 20% of patients with bipolar disorder, but approval would be just the first step for J&J. The company has already submitted a marketing application for general bipolar disorder, which is scheduled to be acted on by the FDA later this year.

An approval seems pretty likely. The drug’s short-acting older sibling, Risperdal, is already approved to treat bipolar disorder, and unlike Eli Lilly's (NYSE:LLY) long-acting version of its antipsychotic, Zyprexa, which the FDA has been reluctant to approve, Risperdal Consta is already approved, making safety issues less likely.

Johnson & Johnson could certainly use the good news. Teva Pharmaceutical (NASDAQ:TEVA) recently launched a generic version of Risperdal and U.S. sales plummeted 84% year over year in the fourth quarter. Gaining some of those bipolar patients back through Risperdal Consta would surely brighten the drugmaker's spirits. Hopefully for investors the delayed-release drug doesn't get a delayed response from the FDA.

Still waiting
While some drugs get responses around the time of their PDUFA dates – six to 10 months after submission -- it seems that an increasingly larger number of drugmakers are being asked to have a seat. Some are getting standard three-month delays; others are being given a more general when-we-get-around-to-it delay.

Eli Lilly and Theravance (NASDAQ:THRX) have had positive FDA panel meetings for their drugs, prasugrel and telavancin, respectively, but neither have gotten a final ruling from the FDA. I think both drugs are likely to be given the thumbs-up, but when they'll get the letter is anyone's guess.

Eli Lilly is also waiting, along with partner Amylin Pharmaceuticals (NASDAQ:AMLN), for a decision from the FDA about the use of Byetta as a monotherapy. The decision, which I'd guess will be positive, is likely to come with a label revision for recently discovered potential side effects. While adding side effects to the label doesn't seem like something the companies would look forward to, that should reassure doctors the FDA has looked at the data and still thinks the benefits outweigh the risks.

Amylin said it expects a decision "later this quarter." Given the FDA's track record, Amylin probably shouldn't be waiting for roses this month.

Approval equals stock pop?
When a drug's approval does come through, it can mean a pop for the company's stock price. But not always. Take tiny GTC Biotherapeutics. It got an approval last week for its anticlotting therapy Atryn and saw its shares fall more than 14%. The same inverted response happened to Onyx Pharmaceuticals (NASDAQ:ONXX) when Nexavar was given the nod for marketing as a liver cancer treatment.

Guessing right about the FDA decision isn't good enough. It's important for investors to also factor in whether the approval is expected or not. This month especially it seems that the FDA decisions are widely expected to be in favor of approval, so if investors overreact and take profits, Fools should be ready to pounce on the stocks at bargain prices.

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Fool contributor Brian Orelli, Ph.D., doesn't own shares of any company mentioned in this article. Johnson & Johnson is a selection of the Income Investor newsletter. We would never make you wait to read The Fool's disclosure policy; just click on through and have a gander.