US regulators have cited four deaths among patients taking Newron Pharmaceuticals’ experimental schizophrenia drug evenamide, placing clinical trials at American sites on hold.

The Food and Drug Administration also flagged irregular heart rhythms in trial participants. One death was recorded among patients on placebo.

Newron shares fell 8.5 percent on the news. The company said enrollment would continue at trial sites outside the United States while it works with the FDA.

Chief Medical Officer Ravi Anand disputed any pattern linking the deaths to evenamide, arguing the fatalities reflected the underlying health risks of the patient population.

The hold is a significant setback for a drug seen as a potential new option for treatment-resistant schizophrenia, a condition with few effective therapies.

Regulators routinely pause trials when safety signals emerge. The key question now is whether Newron can convince the FDA that the deaths were coincidental, or whether the program faces deeper problems.