Terpin hydrate is an expectorant commonly used to loosen mucus in patients presenting with acute or chronic bronchitis, and related conditions. Terpin is derived from oil of turpentine, oregano, thyme and eucalyptus. In 1855 Lepin who first investigated terpin reported that it acted upon the mucous membranes and also the nervous system in a manner similar to the oil of turpentine. Terpin hydrate was available in the USA in 1907 in the preparations such as Elixir of Terpin Hydrate alone or in combination with codein or heroin as an antitussives. It was banned by the U.S. Food and Drug Administration (FDA) in the 1990s due to lack of proof of efficacy but is a medicine available in a number of countries worldwide commonly used in combination with codein. At present it is FDA approved for as an OTC use in combination formulations (with acetaminophen and other drugs) used as internal analgesics. Terpin was recently introduced as a natural topical insect repellent.