Open Source Apothecary At Home / Safety

Herbal liver injury, and the plant that ends the matter

Some plant toxicity is dose-dependent, some is idiosyncratic, and one group is unacceptable at any dose.

safety

Herbal hepatotoxicity is a small share of all liver injury and a large share of the preventable cases, because the exposure is voluntary. The mechanisms separate into groups that need different handling.

Idiosyncratic injury. A reaction in a susceptible individual, at a normal dose, that cannot be predicted by dose. Kava and several Chinese herbal mixtures are the recurring examples. Because it is idiosyncratic, a normal dose is not reassurance.

Intrinsic, dose-related injury. Pyrrolizidine alkaloids and, most severely, aristolochic acid. These are a toxicity of the substance, not of the person.

Aristolochic acid is the plant that ends the argument about tradition. It is present in Aristolochia species — Aristolochia clematitis, birthwort, and the traditional Aristolochia fangchi — used historically for arthritis, and in some herbal weight-loss formulations. It causes aristolochic acid nephropathy, a progressive kidney failure, and it is a potent mutagen and a recognised cause of urothelial cancer. There is no dose at which the traditional use becomes defensible. Species in the genus must simply not be taken, and a product that might contain them must not be taken.

Pyrrolizidine alkaloids occur in comfrey, borage, coltsfoot and some Senecio. They cause hepatic sinusoidal obstruction syndrome at sufficient cumulative dose. Comfrey leaf and root preparations are the common household exposure; the risk is cumulative rather than single-dose, which is exactly why occasional use of a small amount has been argued about for decades while regular internal use has not.

What a household does with this:

• Do not take Aristolochia, any product that might contain it, or anything sold as a
• Do not use comfrey internally, and treat its topical use as short-term on intact skin.
• Check for unexplained fatigue, dark urine or jaundice after starting any herbal
• Where a liver condition already exists, treat every herbal product as a drug to be

What the studies found

Cautions and interactions

• Aristolochia species (birthwort and relatives) — do not take, at any dose. They cause kidney failure and cancer.
• Comfrey, borage, coltsfoot: internal use carries cumulative pyrrolizidine alkaloid exposure. Topical use on intact skin for a short period is the defensible position.
• Kava, greater celandine, germander, and multi-herb Chinese formulas have each been implicated in idiosyncratic liver injury.
• A supplement taken for a liver complaint is still a supplement. Milk thistle is not a treatment for acetaminophen overdose — that is N-acetylcysteine, given promptly, in hospital.

When this is not a self-care problem — get help

• Acetaminophen/paracetamol overdose requires N-acetylcysteine as soon as possible. Go to an emergency department now. Do not wait for symptoms; early overdose feels fine and destroys the liver over days.
• Any jaundice, dark urine, pale stool, unexplained bruising or a swollen, painful abdomen — same-day medical assessment.

Related

• Herb-drug interactions: the ones with numbers behind them
• Alcohol and the liver
• Liquorice, glycyrrhizin, and the potassium it costs you

Sources

1. Clinical and safety outcomes associated with aristolochic acid exposure: a systematic review and meta-analysis. Toxicology mechanisms and methods 2025; doi:10.1080/15376516.2025.2457340 PubMed 39844365
2. Risk assessment of upper tract urothelial carcinoma related to aristolochic acid. Cancer epidemiology, biomarkers & prevention : a publication of the American Association for Cancer Research, cosponsored by the American Society of Preventive Oncology 2013; doi:10.1158/1055-9965.EPI-12-1386 PubMed 23462915
3. Milk thistle for alcoholic and/or hepatitis B or C virus liver diseases. The Cochrane database of systematic reviews 2007; doi:10.1002/14651858.CD003620.pub3 PubMed 17943794
4. Milk thistle for alcoholic and/or hepatitis B or C virus liver diseases. The Cochrane database of systematic reviews 2005; doi:10.1002/14651858.CD003620.pub2 PubMed 15846671
5. Epigenetic modifications in drug-induced liver injury: A systematic review. British journal of clinical pharmacology 2025; doi:10.1111/bcp.70053 PubMed 40441699
6. Epigenetic modifications in drug-induced liver injury: A systematic review. British journal of clinical pharmacology 2025; doi:10.1002/bcp.70053 PubMed 40134104