Black Horehound

What Is Black Horehound?

Black horehound is a strong-smelling perennial of the mint family whose flowering tops are a traditional European remedy for nausea, vomiting and digestive spasms. It has also long been used for nervous tension ^{20,21,23Reference 20Dodd et al. · 2022RCTThe chronic effects of a combination of herbal extracts (Euphytose®) on psychological mood state and response to a laboratory stressor — randomised, placebo-controlled, double-blind RCTView study →Reference 21Health Canada et al. · 2025ReviewBlack Horehound – Ballota nigra — natural health product monograph (uses, dose, contraindications). https://webprod.hc-sc.gc.ca/nhpid-bdipsn/atReq?atid=black.horehound.ballote.noire2&lang=engView study →Reference 23Native Plant Trust (n.d.)Ballota nigra (black-horehound) — species characteristics, habitat and distribution — species databaseView study →}.

It is a common wayside plant of Europe, North Africa and western Asia, growing near towns and villages and on disturbed ground ^{22,23,24Reference 22Grieve · 1931Horehound, Black — description, history and medicinal useView study →Reference 23Native Plant Trust (n.d.)Ballota nigra (black-horehound) — species characteristics, habitat and distribution — species databaseView study →Reference 24GBIF Secretariat (n.d.)Ballota nigra LView study →}. Its offensive smell gave it the old name “black stinking horehound”, and cattle refuse it ^{22Reference 22Grieve · 1931Horehound, Black — description, history and medicinal useView study →}.

The flowering tops carry a family of phenylpropanoid glycosides, chief among them verbascoside ^{3,6Reference 3Seidel et al. · 1998Diterpene and phenylpropanoid heteroside esters from Ballota nigra L. — phytochemicalView study →Reference 6Seidel et al. · 2000In vitroPhenylpropanoids from Ballota nigra L. inhibit in vitro LDL peroxidation — in vitroView study →}. Laboratory studies have looked at their antioxidant, antibacterial and receptor-binding activity; there is no human trial of the herb on its own ^{5,20Reference 5Daels-Rakotoarison et al. · 2000In vitroNeurosedative and antioxidant activities of phenylpropanoids from Ballota nigra — in vitro / animal model (rat tissue)View study →Reference 20Dodd et al. · 2022RCTThe chronic effects of a combination of herbal extracts (Euphytose®) on psychological mood state and response to a laboratory stressor — randomised, placebo-controlled, double-blind RCTView study →}.

Black horehound is a different plant from white horehound, Marrubium vulgare, though Grieve records Marrubium nigrum as an old synonym ^{22Reference 22Grieve · 1931Horehound, Black — description, history and medicinal useView study →}.

How Is Black Horehound Used?

Black horehound is taken for nausea and vomiting, including motion sickness, and for digestive spasms and nervous tension ^{21,23Reference 21Health Canada et al. · 2025ReviewBlack Horehound – Ballota nigra — natural health product monograph (uses, dose, contraindications). https://webprod.hc-sc.gc.ca/nhpid-bdipsn/atReq?atid=black.horehound.ballote.noire2&lang=engView study →Reference 23Native Plant Trust (n.d.)Ballota nigra (black-horehound) — species characteristics, habitat and distribution — species databaseView study →}.

• Tea — an infusion of the dried flowering tops.
• Liquid extract or tincture — the traditional form in British herbal practice ^{22Reference 22Grieve · 1931Horehound, Black — description, history and medicinal useView study →}.
• Combination products — a small amount of black horehound extract is included in Euphytose, a product with valerian, passionflower and hawthorn ^{20Reference 20Dodd et al. · 2022RCTThe chronic effects of a combination of herbal extracts (Euphytose®) on psychological mood state and response to a laboratory stressor — randomised, placebo-controlled, double-blind RCTView study →}.

Traditional Uses

Western Herbal Medicine

In Western herbal medicine black horehound is used as an antiemetic for nausea and vomiting, and as an antispasmodic for digestive spasms ^{21Reference 21Health Canada et al. · 2025ReviewBlack Horehound – Ballota nigra — natural health product monograph (uses, dose, contraindications). https://webprod.hc-sc.gc.ca/nhpid-bdipsn/atReq?atid=black.horehound.ballote.noire2&lang=engView study →}. It has been used for motion sickness and morning sickness ^{23Reference 23Native Plant Trust (n.d.)Ballota nigra (black-horehound) — species characteristics, habitat and distribution — species databaseView study →}.

Grieve describes it as antispasmodic, stimulant and vermifuge, and gives it as a liquid extract ^{22Reference 22Grieve · 1931Horehound, Black — description, history and medicinal useView study →}.

It has a long history of use for anxiety and nervous tension ^{20Reference 20Dodd et al. · 2022RCTThe chronic effects of a combination of herbal extracts (Euphytose®) on psychological mood state and response to a laboratory stressor — randomised, placebo-controlled, double-blind RCTView study →}.

Classical European Medicine

The name ballote goes back to Dioscorides. Both Dioscorides and Gerard held the plant to be an antidote to the bite of a mad dog ^{22Reference 22Grieve · 1931Horehound, Black — description, history and medicinal useView study →}.

Indications

• Nausea and vomiting [flowering tops; Western herbal medicine] ⚠Caution: No study has tested the antiemetic effect, in animals or in people.
• Motion sickness [flowering tops; Western herbal medicine]
• Digestive spasms [flowering tops; Western herbal medicine]
• Nervous tension and anxiety [flowering tops; Western herbal medicine]
• Intestinal worms [herb; Western herbal medicine]
• Bite of a rabid dog [herb; classical European medicine]
• Raised cholesterol and blood sugar [aerial-part extract]

Botany

Black horehound is a perennial herb in the mint family (Lamiaceae), growing up to 130 cm tall from a woody, fibrous root ^{22,23Reference 22Grieve · 1931Horehound, Black — description, history and medicinal useView study →Reference 23Native Plant Trust (n.d.)Ballota nigra (black-horehound) — species characteristics, habitat and distribution — species databaseView study →}. Its stems are square and branched ^{22,23Reference 22Grieve · 1931Horehound, Black — description, history and medicinal useView study →Reference 23Native Plant Trust (n.d.)Ballota nigra (black-horehound) — species characteristics, habitat and distribution — species databaseView study →}.

The leaves grow in opposite pairs, each pair at right angles to the one below. They are stalked, egg-shaped and wrinkled, 3–8 cm long, with coarsely toothed edges and a covering of soft grey hairs ^{22,23Reference 22Grieve · 1931Horehound, Black — description, history and medicinal useView study →Reference 23Native Plant Trust (n.d.)Ballota nigra (black-horehound) — species characteristics, habitat and distribution — species databaseView study →}.

The flowers are dull purple to pink, occasionally white, and grow in dense whorls where the leaves meet the stem ^{22,23Reference 22Grieve · 1931Horehound, Black — description, history and medicinal useView study →Reference 23Native Plant Trust (n.d.)Ballota nigra (black-horehound) — species characteristics, habitat and distribution — species databaseView study →}. Each flower is two-lipped: the upper lip is erect and slightly hollowed, and the lower lip is split into three lobes, the middle one largest ^{22Reference 22Grieve · 1931Horehound, Black — description, history and medicinal useView study →}. The tubular calyx is sharply ribbed and ends in five short, spreading teeth, each tipped with a stiff bristle ^{22Reference 22Grieve · 1931Horehound, Black — description, history and medicinal useView study →}. In Britain it flowers from June to October ^{22Reference 22Grieve · 1931Horehound, Black — description, history and medicinal useView study →}.

The whole plant has a strong, unpleasant smell. The genus name comes from the Greek ballo, “to reject”, because cattle refuse it ^{22Reference 22Grieve · 1931Horehound, Black — description, history and medicinal useView study →}.

Several varieties of Ballota nigra have been named ^{23Reference 23Native Plant Trust (n.d.)Ballota nigra (black-horehound) — species characteristics, habitat and distribution — species databaseView study →}. Research papers name the subspecies they studied, among them foetida, nigra, anatolica and uncinata ^{14Reference 14Erdogan-Orhan et al. · 2010In vitroRadical quenching, ferric-reducing power and ferrous-ion chelating capacity of 16 Ballota species — in vitroView study →}.

Distribution

Black horehound is native to most of Europe, to North Africa from Morocco to Libya, to the Azores, Madeira and the Canary Islands, and to Turkey, Cyprus, the Levant, Iraq, Iran and the Caucasus ^{24Reference 24GBIF Secretariat (n.d.)Ballota nigra LView study →}. In Britain and Ireland it is considered introduced ^{24Reference 24GBIF Secretariat (n.d.)Ballota nigra LView study →}.

It has naturalised in central Asia and western Siberia, northeastern Argentina, the North Island of New Zealand and scattered places in the eastern United States ^{23,24Reference 23Native Plant Trust (n.d.)Ballota nigra (black-horehound) — species characteristics, habitat and distribution — species databaseView study →Reference 24GBIF Secretariat (n.d.)Ballota nigra LView study →}.

It grows on roadsides and waste ground and in other places disturbed by people, and is mostly found near towns and villages ^{22,23Reference 22Grieve · 1931Horehound, Black — description, history and medicinal useView study →Reference 23Native Plant Trust (n.d.)Ballota nigra (black-horehound) — species characteristics, habitat and distribution — species databaseView study →}.

Growing Conditions

Cultivation snapshot for Black Horehound

LifeperennialZoneUSDA 5–9

• Hardy perennial, full sun to part shade; roughly USDA zone 5–9.
• Thrives in disturbed, nutrient-rich soil — hedgerows, roadsides, waste ground.

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Pharmacology & Research

Black horehound has a small, almost entirely preclinical literature, most of it from a few French, Turkish and Italian groups. A family of phenylpropanoid glycosides in the flowering tops (verbascoside, forsythoside B, arenarioside and ballotetroside) carries most of the measured antioxidant, LDL-protective, antibacterial and receptor-binding activity ^{3,5,6Reference 3Seidel et al. · 1998Diterpene and phenylpropanoid heteroside esters from Ballota nigra L. — phytochemicalView study →Reference 5Daels-Rakotoarison et al. · 2000In vitroNeurosedative and antioxidant activities of phenylpropanoids from Ballota nigra — in vitro / animal model (rat tissue)View study →Reference 6Seidel et al. · 2000In vitroPhenylpropanoids from Ballota nigra L. inhibit in vitro LDL peroxidation — in vitroView study →}.

These phenylpropanoids bind benzodiazepine, dopamine and opioid receptors in rat brain preparations ^{5Reference 5Daels-Rakotoarison et al. · 2000In vitroNeurosedative and antioxidant activities of phenylpropanoids from Ballota nigra — in vitro / animal model (rat tissue)View study →}.

The only human data come from a small randomised crossover trial of Euphytose, a four-herb product in which black horehound is a minor ingredient ^{20Reference 20Dodd et al. · 2022RCTThe chronic effects of a combination of herbal extracts (Euphytose®) on psychological mood state and response to a laboratory stressor — randomised, placebo-controlled, double-blind RCTView study →}.

1. Antioxidant

Antioxidant activity is the herb’s most consistently reproduced property, all of it measured in laboratory assays.

Ethanol extracts of 16 Turkish Ballota species all inhibited superoxide formation. Ballota nigra subsp. anatolica was among the nine with marked activity, though not among the strongest ^{8Reference 8Citoğlu et al. · 2004In vitroAntioxidant properties of Ballota species growing in Turkey — in vitroView study →}.

A second screen of 16 Ballota species, including four B. nigra subspecies, found the extracts weak against the DPPH radical, moderate in ferric-reducing power and strong in ferrous-ion chelation ^{14Reference 14Erdogan-Orhan et al. · 2010In vitroRadical quenching, ferric-reducing power and ferrous-ion chelating capacity of 16 Ballota species — in vitroView study →}.

In B. nigra shoots, phenolic and flavonoid content was higher at flowering than in immature plants, and tracked antioxidant activity ^{18Reference 18Makowczyńska et al. · 2015In vitroAntioxidant activity of tissue culture-raised Ballota nigra L. plants grown ex vitro — in vitroView study →}.

The phenylpropanoid esters verbascoside, forsythoside B, arenarioside, ballotetroside and caffeoyl-malic acid scavenged superoxide, hydrogen peroxide, hypochlorous acid and hydroxyl radicals at potencies comparable to N-acetylcysteine ^{5Reference 5Daels-Rakotoarison et al. · 2000In vitroNeurosedative and antioxidant activities of phenylpropanoids from Ballota nigra — in vitro / animal model (rat tissue)View study →}.

2. Neurosedative & Anxiolytic

Five phenylpropanoids isolated from a hydroalcoholic extract (verbascoside, forsythoside B, arenarioside, ballotetroside and caffeoyl-malic acid) were tested for binding to benzodiazepine, dopamine and opioid receptors in rat striatum and whole-brain preparations. Four of the five bound, with IC₅₀ values of 0.4–4.7 mg/mL ^{5Reference 5Daels-Rakotoarison et al. · 2000In vitroNeurosedative and antioxidant activities of phenylpropanoids from Ballota nigra — in vitro / animal model (rat tissue)View study →}.

This is binding affinity in tissue, not a behavioural or clinical result.

The only human data come from a randomised, placebo-controlled crossover trial in 31 healthy adults. Fourteen days of Euphytose, which combines valerian, passionflower, hawthorn and black horehound, reduced tension-anxiety and blunted the stress response to a laboratory stressor ^{20Reference 20Dodd et al. · 2022RCTThe chronic effects of a combination of herbal extracts (Euphytose®) on psychological mood state and response to a laboratory stressor — randomised, placebo-controlled, double-blind RCTView study →}. Each tablet contained 10 mg of black horehound extract from the flowering tops, so the effect cannot be assigned to it ^{20Reference 20Dodd et al. · 2022RCTThe chronic effects of a combination of herbal extracts (Euphytose®) on psychological mood state and response to a laboratory stressor — randomised, placebo-controlled, double-blind RCTView study →}.

Gap: no behavioural animal model and no trial of black horehound alone.

3. Antimicrobial

The isolated phenylpropanoids verbascoside, forsythoside B and arenarioside showed moderate activity against Proteus mirabilis and Staphylococcus aureus, including a methicillin-resistant strain ^{4Reference 4Didry et al. · 1999In vitroIsolation and antibacterial activity of phenylpropanoid derivatives from Ballota nigra — in vitroView study →}.

Fractions of root, stem and leaf extracts inhibited a panel of bacteria, fungi and Leishmania, with the strongest inhibition against Escherichia coli ^{16Reference 16Ullah et al. · 2014In vitroIn vitro antimicrobial and antiprotozoal activities, phytochemical screening and heavy-metals toxicity of different parts of Ballota nigra — in vitroView study →}.

In a screen of 104 Italian medicinal plants, B. nigra was one of ten species that inhibited biofilm formation by MRSA at IC₅₀ ≤ 32 µg/mL, with little effect on bacterial growth ^{11Reference 11Quave et al. · 2008In vitroEffects of extracts from Italian medicinal plants on planktonic growth, biofilm formation and adherence of methicillin-resistant Staphylococcus aureus — in vitroView study →}. A follow-up showed dose-dependent inhibition of staphylococcal quorum sensing ^{15Reference 15Quave et al. · 2011In vitroQuorum sensing inhibitors of Staphylococcus aureus from Italian medicinal plants — in vitroView study →}. Together these point to an anti-virulence rather than a bactericidal action.

4. Anticholesterolemic

In vitro, the four phenylpropanoid glycosides (verbascoside, forsythoside B, arenarioside and ballotetroside) and caffeoyl-malic acid inhibited copper-induced oxidation of low-density lipoprotein, with ED₅₀ values of 1–9.5 µM against 2.3 µM for quercetin. Unlike quercetin, they do not bind copper, so the effect is direct ^{6Reference 6Seidel et al. · 2000In vitroPhenylpropanoids from Ballota nigra L. inhibit in vitro LDL peroxidation — in vitroView study →}.

In vivo, ten rats given a 70% ethanol extract (400 mg/kg for 7 days) had lower total cholesterol, blood glucose and creatine kinase. Liver markers (AST, ALT, bilirubin), triglycerides and troponin I were unchanged ^{9Reference 9Nusier et al. · 2007AnimalEffects of Ballota nigra on blood biochemical parameters and insulin in albino rats — animal model (rat)View study →}.

Gap: LDL-oxidation inhibition is a laboratory surrogate, not a clinical lipid outcome. The only in vivo result is one small rat study, with no human lipid data.

5. Hypoglycemic

A single research group reported glucose-lowering effects in rats. A 70% ethanol extract (400 mg/kg by mouth) lowered blood glucose and, in a glucose-tolerance test, raised serum insulin at 15 and 30 minutes, suggesting an insulin-releasing action ^{9Reference 9Nusier et al. · 2007AnimalEffects of Ballota nigra on blood biochemical parameters and insulin in albino rats — animal model (rat)View study →}. A companion study found that an aqueous extract lowered glucose in both healthy and alloxan-diabetic rats ^{10Reference 10Nusier et al. · 2007AnimalEffects of Ballota nigra on glucose and insulin in alloxan-diabetic albino rats — animal model (rat)View study →}.

Gap: both studies come from one group in the same year, with no independent replication and no human data.

6. Antifungal

The essential oil distilled from the flowering aerial parts, dominated by beta-caryophyllene, germacrene D and caryophyllene oxide, was active in vitro against three Candida species ^{13Reference 13Fraternale et al. · 2009In vitroEssential oil composition and antimicrobial activity of Ballota nigra L. ssp. foetida — in vitroView study →} and against plant-pathogenic fungi (Fusarium, Botrytis cinerea, Alternaria solani) ^{17Reference 17Fraternale et al. · 2014In vitroEssential oil composition and antifungal activity of aerial parts of Ballota nigra ssp. foetida collected at flowering and fruiting times — in vitroView study →}. The authors proposed the oil as an agricultural control agent ^{17Reference 17Fraternale et al. · 2014In vitroEssential oil composition and antifungal activity of aerial parts of Ballota nigra ssp. foetida collected at flowering and fruiting times — in vitroView study →}.

Extract fractions of the root, stem and leaf also inhibited fungi in vitro ^{16Reference 16Ullah et al. · 2014In vitroIn vitro antimicrobial and antiprotozoal activities, phytochemical screening and heavy-metals toxicity of different parts of Ballota nigra — in vitroView study →}.

Gap: the strongest data are for the volatile essential oil, which is not the preparation black horehound is taken as.

7. Anti-Inflammatory

Verbascoside, the main phenylpropanoid, is a well-studied anti-inflammatory molecule in its own right. The B. nigra phenylpropanoids scavenge the reactive oxygen species released by activated neutrophils, acting through protein kinase C and phospholipase C pathways ^{5Reference 5Daels-Rakotoarison et al. · 2000In vitroNeurosedative and antioxidant activities of phenylpropanoids from Ballota nigra — in vitro / animal model (rat tissue)View study →}.

There is no whole-herb anti-inflammatory study.

8. Anticancer

In a screen of three Ballota essential oils against human liver-cancer (HepG2) and breast-cancer (MCF-7) cells, the most active oils were those of B. undulata and B. saxatilis, not B. nigra subsp. foetida ^{19Reference 19Rigano et al. · 2017In vitroPhytochemical profile of three Ballota species essential oils and effects on human cancer cells — in vitroView study →}.

Mechanisms

The phenylpropanoid glycosides of the flowering tops, verbascoside chief among them, have been studied as radical scavengers, as inhibitors of LDL oxidation, and for their binding to benzodiazepine, dopamine and opioid receptors in rat brain tissue ^{5,6Reference 5Daels-Rakotoarison et al. · 2000In vitroNeurosedative and antioxidant activities of phenylpropanoids from Ballota nigra — in vitro / animal model (rat tissue)View study →Reference 6Seidel et al. · 2000In vitroPhenylpropanoids from Ballota nigra L. inhibit in vitro LDL peroxidation — in vitroView study →}. Extracts also inhibit bacterial biofilms and quorum sensing ^{11,15Reference 11Quave et al. · 2008In vitroEffects of extracts from Italian medicinal plants on planktonic growth, biofilm formation and adherence of methicillin-resistant Staphylococcus aureus — in vitroView study →Reference 15Quave et al. · 2011In vitroQuorum sensing inhibitors of Staphylococcus aureus from Italian medicinal plants — in vitroView study →}.

The glucose-lowering effect in rats came from a whole extract, and its active constituent is not known ^{9Reference 9Nusier et al. · 2007AnimalEffects of Ballota nigra on blood biochemical parameters and insulin in albino rats — animal model (rat)View study →}.

Clinical Trials

No trial has tested black horehound on its own. The single registered, completed human study (NCT03909906) used Euphytose, a four-herb combination containing 10 mg of black horehound extract per tablet ^{20Reference 20Dodd et al. · 2022RCTThe chronic effects of a combination of herbal extracts (Euphytose®) on psychological mood state and response to a laboratory stressor — randomised, placebo-controlled, double-blind RCTView study →}. The rest of the evidence base is preclinical.

Last checked: February 2025.

Phytochemistry

The flowering aerial parts carry four phenylpropanoid glycosides, verbascoside, forsythoside B, arenarioside and ballotetroside, which were reported from the genus for the first time in B. nigra and are characteristic of the species ^{2,3Reference 2Seidel et al. · 1997A phenylpropanoid glycoside from Ballota nigra — phytochemicalView study →Reference 3Seidel et al. · 1998Diterpene and phenylpropanoid heteroside esters from Ballota nigra L. — phytochemicalView study →}. They are its major polyphenols ^{6Reference 6Seidel et al. · 2000In vitroPhenylpropanoids from Ballota nigra L. inhibit in vitro LDL peroxidation — in vitroView study →}. Further phenylpropanoid glycosides (alyssonoside, lavandulifolioside, angoroside A) and caffeoyl-L-malic acid were isolated later ^{4Reference 4Didry et al. · 1999In vitroIsolation and antibacterial activity of phenylpropanoid derivatives from Ballota nigra — in vitroView study →}.

The tops also contain labdane-type diterpenoids of the marrubiin family, including marrubiin, 7α-acetoxymarrubiin, ballotenol, ballotinone, hispanolone and preleosibirin. One diterpene, 13-hydroxyballonigrinolide, was isolated from the flowering tops ^{3Reference 3Seidel et al. · 1998Diterpene and phenylpropanoid heteroside esters from Ballota nigra L. — phytochemicalView study →}. Two major flavonoids have been described ^{7Reference 7Bertrand et al. · 2000Two major flavonoids from Ballota nigra — phytochemicalView study →}.

The essential oil of the flowering aerial parts is rich in sesquiterpenes. In one analysis its main components were β-caryophyllene (20.0%), germacrene D (18.0%) and caryophyllene oxide (15.0%) ^{13Reference 13Fraternale et al. · 2009In vitroEssential oil composition and antimicrobial activity of Ballota nigra L. ssp. foetida — in vitroView study →}. Oil from the root is different, led by p-vinylguaiacol, borneol and myrtenol ^{12Reference 12Vukovic et al. · 2009In vitroAntimicrobial activity of the essential oil from roots and volatile constituents of Ballota nigra from Serbia — in vitroView study →}.

Phenolic and flavonoid content is higher in flowering plants than in immature ones ^{18Reference 18Makowczyńska et al. · 2015In vitroAntioxidant activity of tissue culture-raised Ballota nigra L. plants grown ex vitro — in vitroView study →}.

Constituent Summary

Main constituents of the flowering tops.

Dosage

Health Canada’s monograph gives 0.3–12 g of dried herb tops per day for adults, as dried herb, tea, tincture or fluid extract ^{21Reference 21Health Canada et al. · 2025ReviewBlack Horehound – Ballota nigra — natural health product monograph (uses, dose, contraindications). https://webprod.hc-sc.gc.ca/nhpid-bdipsn/atReq?atid=black.horehound.ballote.noire2&lang=engView study →}. No human trial has tested a dose of black horehound on its own.

Traditional Dosage

Safety & Pregnancy

Black horehound is generally well tolerated at customary doses, though its safety has not been formally studied in people. It should not be used in pregnancy ^{21Reference 21Health Canada et al. · 2025ReviewBlack Horehound – Ballota nigra — natural health product monograph (uses, dose, contraindications). https://webprod.hc-sc.gc.ca/nhpid-bdipsn/atReq?atid=black.horehound.ballote.noire2&lang=engView study →}.

Full Safety Detail

Tolerability. Black horehound is generally well tolerated, with few adverse effects reported at customary doses. Its safety has never been formally studied in humans. Allergic reactions have been noted, so a small test dose is sensible on first use.

Interactions. No interaction study of black horehound exists. Its phenylpropanoids bind benzodiazepine, dopamine and opioid receptors in rat brain tissue ^{5Reference 5Daels-Rakotoarison et al. · 2000In vitroNeurosedative and antioxidant activities of phenylpropanoids from Ballota nigra — in vitro / animal model (rat tissue)View study →}, so additive effects are possible with sedatives, antipsychotics and anti-Parkinson’s (dopaminergic) medicines. None has been documented in people.

Iron. It is traditionally said to reduce iron uptake, so taking it apart from iron supplements is a sensible precaution.

Contamination. One analysis found chromium, iron, cadmium and lead above WHO limits in the root, stem and leaf, and nickel above the limit in the root and leaf ^{16Reference 16Ullah et al. · 2014In vitroIn vitro antimicrobial and antiprotozoal activities, phytochemical screening and heavy-metals toxicity of different parts of Ballota nigra — in vitroView study →}. Heavy-metal content reflects where a plant was grown, so buying from a supplier that tests for heavy metals is the practical answer.

References

1. Seidel, V., Bailleul, F., & Tillequin, F. (1996). Phenylpropanoid glycosides from Ballota nigra — in vitro / phytochemical. Planta Medica. https://pubmed.ncbi.nlm.nih.gov/17252437/
2. Seidel, V., Bailleul, F., Libot, F., & Tillequin, F. (1997). A phenylpropanoid glycoside from Ballota nigra — phytochemical. Phytochemistry. https://pubmed.ncbi.nlm.nih.gov/9041717/
3. Seidel, V., Bailleul, F., & Tillequin, F. (1998). Diterpene and phenylpropanoid heteroside esters from Ballota nigra L. — phytochemical. Annales Pharmaceutiques Françaises. https://pubmed.ncbi.nlm.nih.gov/9770033/
4. Didry, N., Seidel, V., Dubreuil, L., Tillequin, F., & Bailleul, F. (1999). Isolation and antibacterial activity of phenylpropanoid derivatives from Ballota nigra — in vitro. Journal of Ethnopharmacology. https://pubmed.ncbi.nlm.nih.gov/10619384/
5. Daels-Rakotoarison, D. A., Seidel, V., Gressier, B., et al. (2000). Neurosedative and antioxidant activities of phenylpropanoids from Ballota nigra — in vitro / animal model (rat tissue). Arzneimittel-Forschung. https://pubmed.ncbi.nlm.nih.gov/10683711/
6. Seidel, V., Verholle, M., Malard, Y., et al. (2000). Phenylpropanoids from Ballota nigra L. inhibit in vitro LDL peroxidation — in vitro. Phytotherapy Research. https://pubmed.ncbi.nlm.nih.gov/10685104/
7. Bertrand, M., Tillequin, F., & Bailleul, F. (2000). Two major flavonoids from Ballota nigra — phytochemical. Biochemical Systematics and Ecology. https://doi.org/10.1016/s0305-1978(00)00015-6
8. Citoğlu, G. S., Coban, T., Sever, B., & Işcan, M. (2004). Antioxidant properties of Ballota species growing in Turkey — in vitro. Journal of Ethnopharmacology. https://pubmed.ncbi.nlm.nih.gov/15138012/
9. Nusier, M. K., Bataineh, H. N., Bataineh, Z. M., & Daradka, H. M. (2007). Effects of Ballota nigra on blood biochemical parameters and insulin in albino rats — animal model (rat). Neuro Endocrinology Letters. https://pubmed.ncbi.nlm.nih.gov/17627272/
10. Nusier, M. K., Bataineh, H. N., Bataineh, Z. M., & Daradka, H. M. (2007). Effects of Ballota nigra on glucose and insulin in alloxan-diabetic albino rats — animal model (rat). Neuro Endocrinology Letters. https://pubmed.ncbi.nlm.nih.gov/17627273/
11. Quave, C. L., Plano, L. R., Pantuso, T., & Bennett, B. C. (2008). Effects of extracts from Italian medicinal plants on planktonic growth, biofilm formation and adherence of methicillin-resistant Staphylococcus aureus — in vitro. Journal of Ethnopharmacology. https://pubmed.ncbi.nlm.nih.gov/18556162/
12. Vukovic, N., Sukdolak, S., Solujic, S., & Niciforovic, N. (2009). Antimicrobial activity of the essential oil from roots and volatile constituents of Ballota nigra from Serbia — in vitro. Journal of Medicinal Food. https://pubmed.ncbi.nlm.nih.gov/19459749/
13. Fraternale, D., Bucchini, A., Giamperi, L., et al. (2009). Essential oil composition and antimicrobial activity of Ballota nigra L. ssp. foetida — in vitro. Natural Product Communications. https://pubmed.ncbi.nlm.nih.gov/19476011/
14. Erdogan-Orhan, I., Sever-Yılmaz, B., Altun, M. L., & Saltan, G. (2010). Radical quenching, ferric-reducing power and ferrous-ion chelating capacity of 16 Ballota species — in vitro. Journal of Medicinal Food. https://pubmed.ncbi.nlm.nih.gov/21091260/
15. Quave, C. L., Plano, L. R., & Bennett, B. C. (2011). Quorum sensing inhibitors of Staphylococcus aureus from Italian medicinal plants — in vitro. Planta Medica. https://pubmed.ncbi.nlm.nih.gov/20645243/
16. Ullah, N., Ahmad, I., & Ayaz, S. (2014). In vitro antimicrobial and antiprotozoal activities, phytochemical screening and heavy-metals toxicity of different parts of Ballota nigra — in vitro. BioMed Research International. https://pubmed.ncbi.nlm.nih.gov/25054139/
17. Fraternale, D., & Ricci, D. (2014). Essential oil composition and antifungal activity of aerial parts of Ballota nigra ssp. foetida collected at flowering and fruiting times — in vitro. Natural Product Communications. https://pubmed.ncbi.nlm.nih.gov/25230517/
18. Makowczyńska, J., Grzegorczyk-Karolak, I., & Wysokińska, H. (2015). Antioxidant activity of tissue culture-raised Ballota nigra L. plants grown ex vitro — in vitro. Acta Poloniae Pharmaceutica. https://pubmed.ncbi.nlm.nih.gov/26647634/
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