SAN DIEGO (AP) -- Neurocrine Biosciences Inc.'s shares sank Monday after the company said that a lower dose one of its drugs under development did not meet the main goal set for it in a clinical trial.

The San Diego-based company is developing a drug for the treatment of tardive dyskinesia, which is a disorder that involves involuntary movements, particularly of the lower face. The movements are one of the muscular side effects of anti-psychotic drugs, especially from some older generation drugs.

Neurocrine Biosciences said that a 50 milligram dose of the drug did not meet a key threshold in inhibiting the movements, while its 100 milligram dose showed a statistical and clinically significant improvement.

Kevin Gorman, President and CEO of Neurocrine said it was not the result the company anticipated in its 50 milligram dose, but the company is pleased to see a clear dose-related response with the larger amount.

Neurocrine said it will now perform an additional Phase II study using 100 milligram and higher doses.

The San Diego company has no products on the market. It is developing treatments for endometriosis pain, uterine fibroids, stress-related disorders, pain, diabetes and insomnia.

Investors were not pleased with the news Monday and sent the stock down $5.21, a 31 percent decline, to $11.49 in after-hours trading.