Tranquilizer, as a term, was first used by F.F. Yonkman (1953), from the conclusions of investigative studies using the drug Reserpine, showed the drug had a calming effect on all animals it was administered to. Reserpine, is a Centrally Acting Rauwolfia Alkaloid. The word directly refers to the state of tranquility in a person and other animals.
The term is generally used as a synonym for sedative. When used by health care professionals, it is usually qualified or replaced with more precise terms: