Stock plummeted more than 56 percent Sept. 29 for Cypress Biosciences, Inc., a San Diego drug development company, closing at $5.53 per share.

Results from a study released Sept. 28 after market close showed its drug Milnacipran, created to treat fibromyalgia, did not prove any more powerful at combating the disease than a placebo in 888 patients. The drug was in a third-stage study, the last phase of trials before the Food and Drug Administration considers it for approval.

Cypress’s stock began falling Sept. 28 after the announcement, dropping from $12.70 to $6.21, then falling again Sept. 29 down to the closing price of $5.53. Overall, the stock is down $7.17, or 56.46 percent.

An analyst with San Francisco-based Merriman Curhan Ford & Co., Adam Noah, said it’s unclear how the 14-employee company will fare.

“It’s hard to know how much hope is left,” he said, adding that such significant declines only happen about twice a month in “the whole universe of biotechs.”

“This is not the endpoint they were looking for,” Noah said.

There is no drug currently approved by the FDA to treat fibromyalgia, but Pfizer, Inc. and Eli Lily & Co., both have drugs already approved for other uses that are now being tested in late-phase trials to treat fibromyalgia.

The disease consists of chronic pain and stiffness, severe fatigue or insomnia and mood symptoms. It affects 6-12 million people, or between 2 and 6 percent of the U.S. population, according to wide-ranging estimates from the Fibromyalgia Resource Center and the National Fibromyalgia Association, both of which receive funding from Cypress.

In early trading Sept. 30, the stock was down 8 cents at $5.45.

At least three investment firms, including Jefferies & Co., Inc. and Punk, Ziegel & Co., have downgraded Cypress stock since this week’s steep decline.

– Katie Weeks