Four inmates at the Hartford Correctional Center were hospitalized after overdosing on fentanyl inside the jail.
Correction Department officials tell The Hartford Courant the inmates, whose names have been released, were found late Thursday night and early Friday morning.
One was in cardiac arrest.
Correction staff had administered the opioid overdose reversal drug Narcan to three of the inmates.
All four were taken to Saint Francis Hospital and Medical Center. Three have since been returned to the jail. The condition of the fourth inmates has not been released.
Officials say they are investigating to determine how the drugs made their way into the high-security jail, which primarily houses prisoners who area awaiting trial.