Common horehound is a perennial herbaceous plant native to the eastern Mediterranean and grown widely in Europe, North Africa, and Central and South Asia since ancient times (figure 14.21). It is now naturalized in temperate North America, Australia, New Zealand, and South Africa.168 Its small, roundish leaves grow opposite each other at nodes along stems 30 to 120 centimeters in height, terminating in spikes of clustered white flowers.169 A member of the mint family, it is aromatic, producing a distinctive aroma and bitter constituents in the leaves and stem.
The Roman scholar Pliny, in his grand opus Natural History, introduced horehound as “a plant too well known to require any description,” which speaks to its widespread cultivation in the ancient Mediterranean world. He lauded horehound’s many uses, including a mixture of ground leaves and seeds for treating snakebites, pain in the torso, and coughs. He also recommended the stems boiled in water for “spitting of blood” and mixed with honey for “affections of the male organs.” Made into an herbal tea with salt and vinegar, Pliny explained, horehound was useful as a laxative, beneficial as a promoter of menstruation, and effective in expelling the afterbirth, in total listing twenty-nine remedies incorporating the herb, against ailments as disparate as jaundice and hangnails.170
FIGURE 14.21 White horehound. (Illustration from Hieronymus Bock, Kreüter Buch ; Peter H. Raven Library, Missouri Botanical Garden, St. Louis, Missouri)
Among the most useful herbs in the classic era, horehound’s reputation followed it through to the seventeenth century, when the herbalist John Parkinson (1567–1650) echoed the advice of ancient authors in recommending it as “a remedy for those that are pursie [asthmatic], and short winded, for those that have a cough.” He also listed it as an antidote to poison, a treatment for sores and ulcers, to improve eyesight, and to open “obstructions both of the liver and spleene.” After an extensive summary of dozens of classical and contemporary applications of horehound, Parkinson encapsulated the prevailing, practical use of the herb: “There is a sirope made of Horehound to be had at the Apothecaries much used, and that to very good purpose for old coughes to rid the tough flegme.”171 While many of the varied uses of horehound failed to transition to the modern era, its preparation into a sweetened syrup or lozenge for respiratory complaints persisted well into the nineteenth century in mainstream medicine (figure 14.22). Although horehound is seldom employed today in formal medical practice, it is an ingredient in extant folk remedies such as Ricola, the Swiss expectorant cough drop.172
FIGURE 14.22 An advertisement for Keating’s Balsam of Horehound, a cough remedy, ca. 1870. (Library of Congress, Prints and Photographs Division, LC-USZ62-51231)
Horehound’s purported medicinal properties are thought to derive from its chemical constituents, including bitter diterpenes such as marrubiin, which accumulate in the herb to 0.3 to 1 percent; some alkaloids; polyphenolics; and volatile oils.173 While experimental evidence is largely restricted to the laboratory rather than trials involving patients, much of the work focusing on marrubiin and its derivatives has shown promise in potential analgesic and anti-inflammatory applications, which might relate to horehound’s classical and folk use against cough and respiratory infections.174 Some of the other chemical constituents, generally less well studied than marrubiin, may also have physiological activity contributing to anti-inflammatory and antimicrobial properties, among others.175 Time and dedicated clinical efforts will establish which of the numerous traditional uses of horehound might be explained by its complex chemistry.