Phenobarbital is a long-acting barbiturate used as a sedative-hypnotic and as an anticonvulsant in the treatment of epilepsy. Phenobarbital exerts its effects by increasing the activity of the inhibitory neurotransmitter GABA and is highly addictive. It was originally discovered in 1912 but it is still commonly used in the clinic and veterinary medicine. It is on the World Health Organization's List of Essential Medicines. Phenobarbital can be detected in the urine for up to 15 days after the last dose.