Nembutal Sodium (Pentobarbital Pills) is a barbiturate (bar-BIT-chur-ate). This medicine slows the activity of your brain and nervous system. Nembutal (Pentobarbital Sodium) is used short-term as a sedative to treatĀ insomnia, or to cause you to fall asleep for surgery. This medicine is also used as an emergency treatment forĀ seizures.