An epilepsy study of the experimental drug called BHV-7000 was paused after regulators requested more information about preclinical safety data, Biohaven revealed in an SEC filing.

Announced mere weeks after Biohaven sold off rights to the therapy, opakalim, the halt affects a study some analysts believe is necessary to support a potential approval.

Biohaven stock plummeted Thursday after the company paused enrollment in a midstage study of its seizure treatment.