Shares in Cypress Bioscience (NASDAQ:CYPB) almost doubled Wednesday, after the company and partner Forest Labs (NYSE:FRX) reported positive phase 3 data late Tuesday for milnacipran to treat fibromyalgia. It's taken awhile, but the run-up caps a turnaround since late September 2005, when the stock fell below $5 per share on disappointing data from a similar trial.

Fibromyalgia is characterized by chronic pain, stiffness, fatigue, and insomnia. There are no approved treatments at present, and it's estimated to affect more than 6 million people in the U.S. alone.

Since 1997, more than 32 countries have approved Cypress' milnacipran to treat depression, using a different mode of action than existing treatments. In 2005, another trial for milnacipran to treat fibromyalgia yielded disappointing data. In the current study, both the low and high dose of the drug achieved statistically significant results in alleviating pain and improving overall functioning in more than 1,000 patients. If the companies receive a favorable review of the full study results, they plan to submit a new drug application to the Food and Drug Administration by the end of the year.

The run-up in Cypress shares Wednesday isn't unreasonable; the company's market cap is still below $600 million, and the study provides encouraging data for a potential new treatment for a fairly common chronic disease. But I would advise investors interested in the name to keep it on their watch list for now, because this is probably not an ideal time for new investors to buy in.

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Fool contributor Mike Havrilla, R.Ph., B.S., Pharm.D., is a full-time  pharmacist who aspires to be a biotech stock analyst. He invites your comments and feedback. Mike does not have a position in any company mentioned in this article. The Fool has a disclosure policy.