Shares of Epix Pharmaceuticals (EPIX) were among health care stocks' losers Friday, plummeting 15.6% on disappointing study results of its experimental anxiety drug.

Epix Pharmaceuticals Inc. said on Thursday that early results from a pivotal-stage trial of its experimental treatment for general anxiety disorder show it does not work better than a placebo.

"Based on these top-line results, we plan to refocus our efforts away from anxiety to evaluate the benefit in depression more closely and assess opportunities for initiating a Phase 2 clinical trial in depression sooner than originally planned," Chief Executive Michael Kauffman said in a statement.

The company said the anxiety trial showed a trend in favor of patients treated with PRX-00023, but the outcome may have been affected by a higher than expected response in the placebo-treated patients.

Epix also said a preliminary review indicated that the treatment was well tolerated and that side effects, including impact on sexual function and sleep, in patients receiving PRX-00023 were similar to placebo.