Pentobarbital (US English) or pentobarbitone (UK English) is a short-acting barbiturate. Pentobarbital can occur as both a free acid and as salts of elements such as sodium and calcium. The free acid is only slightly soluble in water and ethanol.

One brand name for this drug is Nembutal, coined by John S. Lundy, who started using it in 1930, from the structural formula of the sodium salt—Na (sodium) + ethyl + methyl + butyl + al (common suffix for barbiturates). Nembutal is trademarked and manufactured by the Danish pharmaceutical company Lundbeck, and is the only injectable form of pentobarbital approved for sale in the United States.