Halothane vapour is an inhalational general anaesthetic. Its systematic name is 2-Bromo-2-chloro-1,1,1-trifluoroethane. It is colourless and pleasant-smelling, but unstable in light. It is packaged in dark-coloured bottles and contains 0.01% thymol as a stabilising agent.

This halogenated hydrocarbon was first synthesized by C. W. Suckling of ICI in 1951 and was first used clinically by M. Johnstone in Manchester in 1956. Once widely used as general anaesthetic, it has largely been replaced by sevoflurane and desflurane for human use. Halothane is still widely used in veterinary surgery and the Third World because of its lower cost.

Halothane rarely shows any ill effects when used once on a patient. After multiple exposures to halothane, however, the risk of developing severe liver damage increases. This is thought to be a result of some of the vapour being metabolised to trifluoroacetic acid via oxidative reactions in the liver. On rare occasions, (less than 1 in 30,000) this triggers an autoimmune reaction , halothane hepatitis which has a mortality rate of somewhere between 30% and 70%. About 20% of halothane administered is metabolised by the liver and the products excreted in the urine. Halothane can also cause malignant hyperthermia.