Pyrrolizidine alkaloids. There's livertoxic ones, and there's benign ones.
Henriette's herbal blog: The myth that comfrey is completely benign just won't die.
Herbal articles: Pyrrolizidine alkaloids.
Henriette's herbal blog: "Coltsfoot" includes both Tussilago and the various species of Petasites.
Henriette's herbal blog: I've avoided plants with livertoxic PAs for years.
Henriette's herbal blog: They're cousins of both flavonoids and humanoids.
Medicinal herbfaq: single herbs.
Henriette's herbal is one of the oldest and largest herbal medicine sites on the net. It's been online since 1995, and is run by Henriette Kress, a herbalist in Helsinki, Finland.
Plant Healer Magazine: Very relevant to the practitioner.
http://www.henriettes-herb.com - Copyright 1995–2017 Henriette Kress.