Horehound

• Horehound has a long record of traditional use with no adverse events in the EU databases, but almost no safety testing. The EU found no side effects, overdoses or deaths reported for horehound medicines in the German drug-safety database, other member states or the standard herbal textbooks it checked, and judged the benefit-risk balance positive for the traditional uses. The same documents also say the usual formal tests for toxicity, cancer risk, gene damage and reproductive harm have not been done, and there are no human absorption data. Absence of reports is not proof of safety. Authoritative guidance ^{3 4 9}
• Avoid in pregnancy and breastfeeding. The EU monograph says safety in pregnancy and breastfeeding has not been established and use is not recommended. The assessment report adds that a rat study showed some abortive activity but a guinea pig and mouse study did not convince, and that one poison-centre case involving horehound in a mixture was not followed by abortion. A consumer reference goes further and calls oral use in pregnancy likely unsafe because it might start menstruation; we found no primary study for that claim. Authoritative guidance ^{3 4 2 18}
• Not for liver disease, bile duct blockage or gut obstruction. The EU monograph lists bile duct obstruction, cholangitis, liver disease and ileus (blocked bowel) as contraindications, and says people with active peptic ulcer, gallstones or other bile duct disorders should consult a doctor first. The documents we read do not explain the reason. Authoritative guidance ³
• Allergy to horehound or other plants in the mint family. The monograph contraindicates use if you are allergic to white horehound or to other plants of the Lamiaceae family (mint, sage, thyme, lavender and relatives). Older sources list horehound juice as a possible cause of contact skin inflammation. Authoritative guidance ^{3 4}
• Possible effects on blood sugar, blood pressure and heart rhythm are cautions, not proven effects. A consumer reference says horehound might lower blood sugar and blood pressure and might cause irregular heartbeat in people with heart problems. The EU assessment report says large amounts may theoretically raise the risk of abnormal heart rhythms and cites a 1976 source without dose or case details. In the one human trial, horehound tea barely changed blood sugar and the EMA says it did not lower blood pressure. The EU monograph lists no interactions. Pharmacological theory ^{18 4 12}
• One case report links a three-plant mixture containing horehound to kidney injury. A 17-year-old developed severe acute kidney failure that the authors attributed to chronic intake of wormwood, white horehound and centaury together. One case with three plants cannot show which plant was responsible, or that horehound was. Case report ¹⁹
• Children under 12. The EU says use in children under 12 is not established for lack of data. A 2024 trial of a five-ingredient syrup that contained horehound in 56 children aged 5 to 11 reported no adverse effects, but that does not clear horehound alone. Authoritative guidance ^{3 15}

We found no published human case of liver injury attributed to white horehound, and no LiverTox entry. The EU monograph nevertheless lists liver disease and bile duct obstruction as contraindications without giving a reason in the documents read. Animal studies and a 2026 review describe liver-protective effects, which are lab findings and say nothing about people with liver disease. ^{3 16}

How often. No frequency of liver injury was found. Not finding reports is not proof that none occur.

Monitoring. No agency monitoring advice was found. Yellow skin or eyes, dark urine or pale stools after taking any herb are reasons to stop and see a doctor. People with liver or bile duct disease should not use it without medical advice (EU monograph).

This is a safety connection. It is not evidence that Horehound supports liver health.

Summary. No poisoning or overdose has been reported for white horehound medicines. The standard toxicity, genotoxicity, cancer and reproductive tests have not been done, according to the EMA.

Animal. The EMA report describes a mouse study where an infusion at 1 g/kg by mouth caused a fast heartbeat after 1 hour and loss of appetite after 3 hours, with no tissue damage, and a rat study where a methanol extract at 2,000 mg/kg showed no toxic signs (toxic dose judged higher than 2,000 mg/kg). Only the EMA summaries were read.

Human doses studied. Leaf infusion of 3 g herb a day for 21 days in 21 people with type 2 diabetes; a five-ingredient syrup for 7 days in 27 children given the active product.

High dose or long term signals. Large amounts may cause vomiting (consumer reference) and, in theory, abnormal heart rhythm (EMA report). No long-term human safety data exist.

Overdose response. No overdose case has been reported (EU monograph). Seek urgent care for chest pain, fainting or a very fast or irregular heartbeat.

Genotoxicity. Not tested (EU monograph: tests on reproductive toxicity, genotoxicity and carcinogenicity have not been performed).

Toxic plant parts. No toxic plant part is named. The aerial parts (leaves, stems, flowers) are used. Some texts also mention the root in traditional use.

The main quality risk is getting the wrong plant. No surveys of heavy metals, pesticides or microbes in horehound products were found.

Look-alike plants. The EMA report says confusion is possible with black horehound (Ballota nigra), catnip (Nepeta cataria), Stachys germanica and two other Marrubium species. It also notes that a herb sold as 'black horehound' in older trade was Marrubium peregrinum. ^{4 10}

Strength varies. The European Pharmacopoeia requires at least 0.7% marrubiin in the dried herb, but marrubiin content varies by season and extraction, and the 2026 review says extract composition and standardisation vary widely. ^{4 16}

Combination products. Many cough and digestive products mix horehound with other herbs; the EU summary does not cover combinations. ⁹

• Chest pain, fainting, a very fast, pounding or irregular heartbeat.
• Yellow skin or eyes, dark urine or pale stools, or severe stomach pain (liver or bile duct problem).
• Swelling of the face, lips or tongue, trouble breathing or a spreading rash (allergy).
• Very little urine, swelling in the legs or sudden tiredness with nausea (kidney problem).
• Shaking, sweating, confusion or faintness in someone on diabetes medicine (low blood sugar).
• A cough with blood, fever, breathlessness, or cough that lasts more than one week.
• Bleeding after surgery that will not stop.

Stop the supplement and contact a clinician or emergency service. In the US, Poison Control is 1-800-222-1222.