Scientific Name(s): Marrubium vulgare (Tourn.) L.
Common Name(s): Hoarhound, Horehound, Maromba, Marroio, White horehound
Horehound is native to Europe and Asia and has been naturalized to other areas, including the United States.1 It is a perennial, aromatic herb of the mint family. The plant grows to a height of approximately 1 m, and has oval leaves covered with white, woolly hairs. Horehound bears small, white flowers in dense whorls, which bloom from June to August.12, 3
The leaves and flower tops of the horehound plant have been traditionally used in the form of a bitter tonic as a home remedy for the common cold. Horehound is now primarily used to flavor liqueurs, candies, and cough drops.4 Although there is no evidence to support use in cough preparations,2, 3 the FDA has granted horehound GRAS status when consumed at concentrations used in such preparations.5 Traditional uses of plant extracts include treatment of intestinal parasites; as a diaphoretic, diuretic, and digestive aid, and appetite stimulant; and in cancer.3, 6 An unrelated species, the black horehound (Ballota nigra), is a fetid-scented perennial native to the Mediterranean region that is sometimes used as an adulterant of white horehound.2
Horehound contains 0.3% to 1% of the bitter principle marrubiin (a diterpene lactone); several diterpene alcohols (eg, marrubiol, marrubenol); and marrubiinic and marrubic acids. Phenylpropanoid esters and glycosides, as well as a phenylethanoid glycoside (marruboside) have been isolated from the aerial parts.2, 7, 8
Additional identified compounds include alkaloids, alkanes, flavonoids, tannin, pectic substances, saponin, and resin; some research has also focused on phenylpropanoid esters (including verbascoside, forsythoside, arenarioside, and ballotetroside) and glycosides.2, 9, 10, 11 Horehound also contains a small amount of essential oil, which is primarily composed of mono- and sesquiterpenes.2
Uses and Pharmacology
In screening studies, extracts of horehound and its essential oil have demonstrated activity against Helicobacter pylori12 and several other human bacterial and fungal pathogens, including methicillin-resistant Staphylococcus aureus.13, 14, 15 Molluscicidal and mosquitocidal properties have also been demonstrated.16
No clinical data exist regarding the use of horehound for antimicrobial activity.
Limited studies in rodents suggest that marrubiin possesses anti-inflammatory and antioxidant activity, which may be beneficial in reducing the effects of myocardial infarction.17, 18, 19 One group of researchers has demonstrated antihypertensive effects of a water extract of horehound in experiments in rodents.20, 21
No clinical data exist regarding the use of horehound in cardiovascular conditions. Older texts suggest that marrubiin has antiarrhythmic properties, which may induce cardiac irregularities in larger doses;3 however, animal and clinical data regarding such properties are lacking.
In a study using an obese rat model, increased insulin secretion and increased low-density lipoprotein cholesterol were achieved by administration of marrubiin, which was extracted from the unrelated Leonotis leonurus plant.7, 22 In rats with induced diabetes, an aqueous extract of M. vulgare aerial plant parts decreased blood glucose and improved lipidemic indices in a dose-dependent manner.23
A study using a hydroalcoholic extract, which was dosed at 300 mg/kg via intraperitoneal injection in streptozotocin-induced diabetic rats, also noted significantly reduced fasting blood glucose (–61%), as well as reductions in total cholesterol and triglycerides of 26% and 15%, respectively.24 These activities were confirmed in another study using a methanolic extract at a dose of 500 mg/kg, in which glycemic reductions were similar to those observed in the comparator glibenclamide, and total cholesterol and triglycerides decreased while high-density lipoprotein increased.25 Some of these effects may result from 6-octadecynoic acid, obtained from the methanol leaf extract of M. vulgare, which has been identified as a potential glucose and lipid regulator that acts in a similar manner to thiazolidinediones such as pioglitazone.26
A small clinical study (N = 43) evaluated the effects of Cecropia obtusifolia and M. vulgare leaf extracts on blood glucose and serum lipid levels in patients with noncontrolled type 2 diabetes with poor response to conventional medical treatment.27 All patients maintained their medical treatment. In the patient group (n = 21) receiving infusions prepared with the leaves of M. vulgare and administered in 1 g envelopes 3 times a day for 21 days, the plasma glucose level was reduced by 0.64% and cholesterol and triglycerides by 4.16% and 5.78%, respectively.27
Limited studies in rodents and in vitro experiments suggest that the chemical constituents of horehound exhibit anti-inflammatory effects. The phenylpropanoid esters acetoside, forsythoside, and arenarioside inhibited cyclooxygenase-catalyzed prostaglandin biosynthesis,10 while marrubiin reduced histamine-, carrageenan-, and formalin-induced edema.7, 28
No clinical data exist regarding the use of horehound for analgesic or anti-inflammatory effects.
No clinical data exist regarding the use of horehound as an expectorant or for stimulation of bile production.
Antispasmodic activity has been demonstrated in isolated tissue experiments, in which calcium channel antagonism and anticholinergic effect were suggested as mechanisms of action.7, 32 Gastroprotective activity has been demonstrated in rats by a methanol horehound extract and by marrubiin.33 Antioxidant activity has also been demonstrated and may be due to the phenolic compounds in the plant leaves.11
Both a methanol extract of horehound aerial parts and an extracted terpenoid were hepatoprotective, as demonstrated in rats on histological examination and in liver enzyme indices.9, 34 An aqueous extract was also found to be protective against cyclophosphamide hepatotoxicity.35
Clinical trials are lacking to provide guidance in dosing. One clinical study evaluating the effect of horehound in type 2 diabetes used horehound infusions prepared with the leaves of M. vulgare and administered in 1 g envelopes, 3 times a day for 21 days.2, 27
Pregnancy / Lactation
Case reports are lacking; however, in vitro studies suggest that marrubiin has anticoagulant and antiplatelet activity,7, 17 while calcium channel blocking activity has been attributed to marrubenol.2 One older study suggested antiserotonin activity.2
In a small clinical study, nausea, dry mouth, excessive salivation, dizziness, and anorexia were reported by some patients drinking an infusion of horehound.27
Older texts suggest that marrubiin has antiarrhythmic properties, which may induce cardiac irregularities in larger doses;3 however, animal and clinical data regarding such properties are lacking.
Marrubiin has an LD50 of 370 mg/kg when administered orally to rats and an LD50 of 100 mg/kg when injected in mice; marrubiin was not cytotoxic to any of the 66 cell lines tested.7 M. vulgare was given to rats at increasing doses of up to 1,000 mg/kg daily for 3 weeks, with no signs of toxicity.25 As a flavoring agent and essential oil, horehound has been granted GRAS status by the FDA.5
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