Some medicinal herbs (plant parts taken for medicinal purposes) contain substances that can damage the liver. These substances may also be consumed in contaminated foods. The liver is a prime target for damage because it processes everything that enters the mouth and is swallowed.

Herbs that contain pyrrolizidine alkaloids may damage the liver. Hundreds of herbs contain pyrrolizidine alkaloids. These herbs include borage, comfrey, and certain Chinese herbs, such as zi cao (groomwell), kuan dong hua (coltsfoot), qian li guang (liferoot), and pei lan (Eupatorium). Some of the herbs that contain pyrrolizidine alkaloids are used to make teas. Sometimes milk, honey, and cereals are contaminated with pyrrolizidine alkaloids, which are then consumed unknowingly.

Pyrrolizidine alkaloids can damage the liver gradually if small amounts are consumed for a long time or more quickly if a large amount is consumed. They may cause the hepatic vein to become clogged, blocking the blood supply to the liver.

Affected people have abdominal pain and may vomit. Fluid accumulates in the abdomen and legs. Eventually, scar tissue in the liver (cirrhosis), liver failure, and even death may result.

Other herbs that can damage the liver include Atractylis gummifera, Camellia sinensis (used to make black tea), celandine (greater), chaparral, germander, jin bu huan, kava, ma huang (Ephedra), mistletoe, pennyroyal oil (used to make teas), and syo-saiko-to (a mixture of herbs).