It is a grey-leaved herbaceousperennial plant, somewhat resembling mint in appearance, and grows to 25–45 centimetres (10–18 in) tall. The leaves are 2–5 cm (0.8–2.0 in) long with a densely crinkled surface, and are covered in downy hairs. The flowers are white, borne in clusters on the upper part of the main stem.
The Oxford English Dictionary derives the word from two Old English forms: "hoar" ("white," "light-colored," as in "hoarfrost") and "hune" a word of unknown origin designating a class of herbs or plants. The second element was altered by folk etymology.
Horehound has been mentioned in conjunction with medicinal use dating at least back to the 1st century BC, where it appeared as a remedy for respiratory ailments in the treatise De Medicina by Roman encyclopaedist Aulus Cornelius Celsus. The Roman agricultural writer Columella lists it as a remedy for expelling worms in farm animals in his important first-century work On Agriculture. Since then, horehound has appeared for similar purposes in numerous herbals over the centuries, such as The Herball, or, Generall historie of plantes by John Gerard, and Every Man His Own Doctor: or, The Poor Planter’s Physician by Dr. John Tennent.
Several modern scientific studies have been conducted on the usefulness of horehound. For example, a 2011 study concluded that the essential oil of M. vulgare contains potent antimicrobial and anticancer properties, while a 2012 study found marrubiin, one of the primary active compounds found in horehound, to possess "antidiabetic, anti-atherogenic and anti-inflammatory properties".
Horehound was introduced to southern Australia in the 19th century as a medicinal herb. It became a weed of native grasslands and pastures where it was introduced with settlers’ livestock, and was first declared under noxious weeds legislation. It now appears to have reached its full potential distribution.
It occupies disturbed or overgrazed ground, and is favoured by grazing because it is highly unpalatable to livestock. It may persist in native vegetation that has been grazed.
A bitter herb, which when dried is used as tea for debility and colds. The plant is also used in certain candies for coughs and sore throat, as an expectorant, as a diaphoretic, and as a laxative when taken in large doses. It is the source of an essential oil used in liqueurs. It is also a honey plant.