Horehound is a perennial plant with small white flowers found growing in the wild throughout Europe and Asia. All parts of the plant are used medicinally.1

Horehound has been used in connection with the following conditions: bronchitis, cough, indigestion.

A natural diuretic, it helps to rid the body of excess water and salt. Helpful in weight control and high blood pressure conditions.

Historical or traditional use (may or may not be supported by scientific studies): Horehound was reportedly first used in ancient Rome by the physician Galen, who recommended it as a therapy for coughs and other respiratory ailments. Like Galen, Nicholas Culpeper, the 17th-century English pharmacist, commented that it was helpful for a cough and was also useful in helping remove stubborn phlegm from the lung. Similarly, American Eclectic physicians (doctors who recommended herbs) of the 19th century remarked on its value as a medicinal plant not only for coughs and asthma but also in menstrual complaints.2

Active constituents: Horehound contains a number of constituents, including alkaloids, flavonoids, diterpenes (e.g., marrubiin), and trace amount of volatile oils.3 The major active constituent in horehound is marrubiin, which is thought to be responsible for the expectorant (promotion of coughing up of mucus) action of the herb. In addition, marrubiin contributes to the bitter taste of horehound, an action that increases the flow of saliva and gastric juice, thereby stimulating the appetite.4 These actions likely explain the long-standing use of horehound as a cough suppressant and expectorant as well as a bitter digestive tonic.

How much is usually taken? For adults, the German Commission E monograph recommends approximately 3/4 teaspoon (4.5 grams) of horehound per day or 2–6 tablespoons (30–90 ml) of the pressed juice.5 Alternatively, horehound tea can be prepared from approximately 1/4–1/2 teaspoon (1–2 grams) of root boiled in about 7 ounces (200 ml) of water for ten minutes. Three cups (750 ml) of this tea can be drunk per day. Horehound is sometimes found in herbal lozenges that are used for coughs.

Since horehound acts as a bitter and may increase production of stomach acid, people with gastritis or peptic ulcer disease should use it cautiously. Horehound should not be used during pregnancy, as it may stimulate contractions.

At the time of writing, there were no well-known drug interactions with horehound.

References:
1. Wren RC., Potter’s New Cyclopaedia of Botanical Drugs and Preparations. Essex, England: C.W. Daniel Co., 1988, 146.
2. Castleman M., The Healing Herbs. Emmaus, PA: Rodale Press, 1991, 216–7.
3. Leung AY, Foster S., Encyclopedia of Common Natural Ingredients Used in Food, Drugs, and Cosmetics, 2d ed. New York: John Wiley & Sons, 1996, 303.
4. Bradley PR., British Herbal Compendium, vol 1. Great Britain: British Herbal Medicine Association, 1990, 218–9.
5. Blumenthal M, Busse WR, Goldberg A, et al. (eds)., The Complete German Commission E Monographs: Therapeutic Guide to Herbal Medicines. Austin: American Botanical Council and Boston: Integrative Medicine Communications, 1998, 127–8.