Phenobarbital is used to control seizures. Phenobarbital is also used to relieve anxiety. It is also used to prevent withdrawal symptoms in people who are dependent (addicted; feel a need to continue taking the medication) on another barbiturate medication and are going to stop taking the medication. It is Contraindicated in patients with acute intermittent porphyria, severe lung insufficiency, and obstructive sleep apnea, liver and kidney disease.