Xenon Pharmaceuticals has temporarily stopped enrolling new patients in clinical studies of azetukalner for major depression and bipolar disorder after reports of mental and nervous system-related side effects. The voluntary pause followed consultations with the trials' safety monitoring board and an analysis of adverse events. Patients already enrolled will continue treatment. Xenon said the side effects' severity and frequency were consistent with how azetukalner worked, although they had not been observed in an earlier mid-stage depression study. The company is assessing dose adjustments to improve tolerability. The pause does not affect azetukalner's epilepsy program, and Xenon has submitted an application to the U.S. Food and Drug Administration (FDA), the country's medicines regulator, seeking approval for focal seizures, the most common form of epilepsy. Xenon Pharmaceuticals shares fell more than 20% in after-hours trading.