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Scientific Name(s): Lycopus europaeus L.
Common Name(s): Bitter bugle, Bugleweed, Carpenter's herb, Green archangel, Gypsywort, Northern bugleweed, Paul's betony, Purple archangel, Rough bugleweed, Sweet bugle, Virginia water horehound, Water bugle, Water horehound, Wolf foot, Wolfstrappkraut

Medically reviewed by Last updated on Jun 27, 2022.

Clinical Overview


Bugleweed is used to treat mild hyperthyroidism, premenstrual syndrome, and breast pain; however, quality clinical studies are lacking to support these uses.


Clinical trials are lacking regarding dosages for specific clinical applications. A daily dosage of Lycopi europaei herba 40 mg/day taken in divided doses was used for 3 months in an open-label clinical study for mild hyperthyroidism.


None specifically identified except pregnancy. Exercise caution in patients with hypothyroidism.


Contraindicated in pregnancy and lactation because of the potential for antigonadotropic and antithyrotropic effects; however, clinical data are lacking.


None well documented.

Adverse Reactions

Clinical trials and case reports are lacking. Bugleweed taken in high amounts or stopped suddenly might theoretically cause thyroid enlargement.


Information is lacking.

Scientific Family

  • Lamiaceae (mint)


Bugleweed is an herbaceous perennial mint that grows in wet habitats. The leaves are toothed, and the small white flowers surround the square stem at the leaf axils in dense clusters. The plant has little odor; the European species has a bitter taste, but the American species is not bitter. The whole herb is used medicinally.1 Other members of the Lycopus (water horehound), including Lycopus asper Greene, Lycopus unifloris Michx., and Lycopus virginicus L., are also broadly termed bugleweed.


Traditional uses of bugleweed include treatment of nosebleeds, heavy menstrual bleeding, and coughs. It has also been used as a sedative, astringent, and mild narcotic, and for tuberculosis characterized by bleeding from the lungs. More current uses are primarily for mild hyperthyroid conditions and for premenstrual syndrome, including breast pain (mastodynia).2, 3, 4


The phenolic compounds lithospermic acid, rosmarinic acid, chlorogenic acid, and caffeic acid have been identified in both L. europaeus and L. virginicus.5, 6 The flavonoids luteolin 7-glucoside, luteolin 3′,7-diglucoside, luteolin 7-glucuronide, and apigenin 7-glucoside have also been isolated from L. europaeus, L. virginicus, and Lycopus lucidus.7, 8, 9, 10 Several isopimarane diterpenes have been isolated as well.11, 12, 13 An automated thin-layer chromatography method for analysis of Lycopus and other plants has been published.14, 15

Uses and Pharmacology

Antigonadotropic effect

Clinical studies are lacking; however, one small clinical trial measured no changes in plasma estradiol, testosterone, follicle-stimulating hormone, or luteinizing hormone levels.2

Flavonoids and phenolics from Lycopus species exert antigonadotropic activity in animal and in vitro experiments.16, 17, 18, 19, 20, 21, 22, 23 Activation of the phenolic compounds appears to be required for effect and may be limited to glycoprotein hormones, including TSH and gonadotropin.24 Extracts showed inhibition of human chorionic gonadotropin binding to rat testis membranes.25 Lycopus extract administration in rats reduced prolactin levels and is thought to be secondary to reduction in TSH because thyroid status influences prolactin production.26

Antioxidant potential

The antioxidant potential of extracts of Lycopus has been demonstrated in vitro and is attributed in part to the phenolic content of the plant.10, 27, 28

Immune-modulating effects

Immune-modulating effects have been demonstrated by extracts of the leaves of L. lucidus, as well as betulinic acid extracted from the aerial plant parts. A reduction in histamine released from mast cells because of membrane stabilization, as well as both increased and decreased secretion of tumor necrosis factor, has been shown.6, 29

Mild hyperthyroidism

The majority of studies on L. europaeus and thyroid activity arise from a small pool of researchers. A review of the thyroid pharmacology of Lycopus has been published.30 Antithyroid activity initially was attributed to lithospermic acid31; however, a more complex mechanism has developed since that early work. It has been proposed that the oxidation of phenolics to unstable orthoquinones by plant enzymes is required for antithyroid activity. Thus, caffeic acid, rosmarinic acid, and lithospermic acid are inactive without some form of oxidation.32, 33

Animal data

Extracts of L. europaeus administered to healthy rats reduced the weight of the thyroid, decreased thyroid hormone activity, and increased absorption and storage of iodine. The extract retarded goiter formation in propylthiouracil-treated rats. All animals treated with the extract demonstrated reduced metabolism.34 Other studies in rats have shown inhibition of serum thyrotropic hormone and thyroxine after oral administration.35 Cardiac signs of hyperthyroidism were reduced in an experiment in rats treated with L. europaeus extract.3

Freeze-dried extracts of bugleweed and other related plants showed a dose-dependent inhibition of bovine thyroid-stimulating hormone (TSH) binding to human thyroid membranes, with simultaneous inhibition of TSH-stimulated adenyl cyclase activity.25, 36 Formation of covalent adducts with TSH amino acid residues was postulated; however, the evidence for this is not conclusive.32

Clinical data

Few clinical studies have been reported, and the methodology in these studies limits the validity of the findings. Randomized, placebo-controlled clinical trials are lacking.

Humans treated with Lycopus extracts showed inhibition of serum thyrotropic hormone and thyroxine37 while a reduction in the thyroid-stimulating effect of thyroid antibodies in Graves disease has been demonstrated.33

Low-dose powdered L. europaeus equivalent to 2 × 5 mg Lycopus extract administered in an observational study produced no changes in thyroid hormone levels but demonstrated improved cardiac symptoms.2, 3

A prospective open study (N = 62) was conducted in patients with mild hyperthyroidism.2 Patients in the treatment arm of the study were given Lycopus herb 40 mg/day, while those in the control arm were managed in a different naturopathic manner. No difference was found in excretion of tri-iodothyronine in the urine; however, an increase was found for thyroxine excretion in the Lycopus-treated patients. Free thyroxine and TSH serum levels also remained unchanged. A renal mechanism has been proposed for the observed effects.2

Vascular inflammation

Vascular inflammation induced by high glucose levels in human cells was inhibited by an aqueous extract of the leaves of L. lucidus.28 Triterpenes from the plant also inhibited cholesterol acyltransferase38 suggesting a potential role in the prevention of atherosclerosis.

Other uses

Inhibition of xanthine oxidase (key to the production of uric acid in gout) by an extract of the leaves of L. europaeus has been demonstrated in vitro.39 Diterpenes extracted from L. europaeus were effective against multidrug resistant Staphylococcal aureus when used in combination with tetracycline or erythromycin.13


A dosage Lycopi europaei herba of 40 mg/day in divided doses was used for 3 months in an open-label clinical study.2 Low-dose powdered L. europaeus equivalent to 2 × 5 mg Lycopus extract used in an observational study produced no changes in thyroid hormone levels but was associated with improved cardiac symptoms.2, 3

Pregnancy / Lactation

Contraindicated in pregnancy and lactation because of the potential for antigonadotropic and antithyrotropic effects, as demonstrated in animal experiments.40, 41 Data on secretion of bugleweed compounds in human breast milk are not available. A reduction of prolactin levels in rats following Lycopus extract administration has been observed26 while no effect on plasma levels of prolactin was found in a clinical study.2


None well documented. The potential for interaction with thyroid medications exists, as well as interference in laboratory values.

Adverse Reactions

In a clinical study (N = 62), 6 adverse events were recorded, one of which (subjective feelings of cardiac rhythm disturbance) was attributed to the active bugleweed preparation.2

A review of natural preparations with the potential to have adverse renal effects included bugleweed; however, the level of evidence is low.42

Bugleweed taken in high amounts or stopped suddenly might theoretically cause thyroid enlargement.30


The potential for serious toxicity appears to be low; however, data are lacking.30

Index Terms

  • Lycopus asper Greene
  • Lycopus unifloris Michx.
  • Lycopus virginicus L.
  • Lycopus
  • Water horehound



This information relates to an herbal, vitamin, mineral or other dietary supplement. This product has not been reviewed by the FDA to determine whether it is safe or effective and is not subject to the quality standards and safety information collection standards that are applicable to most prescription drugs. This information should not be used to decide whether or not to take this product. This information does not endorse this product as safe, effective, or approved for treating any patient or health condition. This is only a brief summary of general information about this product. It does NOT include all information about the possible uses, directions, warnings, precautions, interactions, adverse effects, or risks that may apply to this product. This information is not specific medical advice and does not replace information you receive from your health care provider. You should talk with your health care provider for complete information about the risks and benefits of using this product.

This product may adversely interact with certain health and medical conditions, other prescription and over-the-counter drugs, foods, or other dietary supplements. This product may be unsafe when used before surgery or other medical procedures. It is important to fully inform your doctor about the herbal, vitamins, mineral or any other supplements you are taking before any kind of surgery or medical procedure. With the exception of certain products that are generally recognized as safe in normal quantities, including use of folic acid and prenatal vitamins during pregnancy, this product has not been sufficiently studied to determine whether it is safe to use during pregnancy or nursing or by persons younger than 2 years of age.

More about bugleweed

Related treatment guides

1. Lycopus europaeus. USDA, NRCS. 2009. The PLANTS Database (, April 2009). National Plant Data Center, Baton Rouge, LA 70874-4490 USA.
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3. Vonhoff C, Baumgartner A, Hegger M, Korte B, Biller A, Winterhoff H. Extract of Lycopus europaeus L. reduces cardiac signs of hyperthyroidism in rats. Life Sci. 2006;78(10):1063-1070.16150466
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5. U.S. Department of Agriculture, Agricultural Research Service. 1992-2016. Dr. Duke's Phytochemical and Ethnobotanical Databases. Home Page,
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