Pentobarbital is in a class of drugs called barbiturates. Pentobarbital slows down activity in the brain and nervous system and is FDA approved to treat short-term insomnia. It is also used to treat seizures and to induce preoperative sleep/sedation. Pentobarbital has also been used in physician-assisted suicides. There are varying side effects associated with taking pentobarbital, including weak or shallow breathing; confusion or hallucinations; slow heart rate or weak pulse; fever or sore throat; or feeling like you may pass out. Similarly, seek emergency medical help if you have any signs of an allergic reaction, including: swelling of your face, lips, tongue, or throat; hives; or difficulty breathing.