Asteraceae
Petasites hybridus
Butterbur · Bog rhubarb
- Part used
- rootrhizomeleaf
- Native range
- Europe and western Asia, in wet ground
- Morphology
- A perennial of riverbanks producing thick pink flower spikes before the leaves, followed by enormous rhubarb-like leaves up to a metre across — large enough to have been used to wrap butter, which is what names it.
What is in it
Evidence
Randomised trials support butterbur extract for migraine prevention, and it was formerly given a favourable rating in American Academy of Neurology guidance. That guidance was subsequently withdrawn — not because the efficacy evidence failed, but because of the safety and manufacturing problems.
Safety
Contains hepatotoxic pyrrolizidine alkaloids, as comfrey does. Commercial preparations are PA-depleted by manufacturing, and the safety of a product therefore depends entirely on the manufacturer rather than on the plant. Liver injury cases led the UK to remove products from sale in 2012 and Germany to withdraw licences. Only PA-free standardised extracts are defensible, and verifying that is not something a purchaser can do.
Interactions: Additive liver risk
Regulatory: Withdrawn or restricted in the UK and Germany. Permitted in Australia subject to PA limits.
How the traditions classify it
Three systems, rating the same plant. Where they disagree, none of them is correcting the others — they are separate frameworks that arrived at their categories independently.
Historical use
Used across Europe for fever, cough and, from the twentieth century, for migraine and allergic rhinitis.
Recorded as history and attributed where possible. Long use establishes that a plant was widely used, not that it worked, and not that it was safe.
Worth knowing
Butterbur is the most uncomfortable entry in this collection, because the efficacy evidence is good and the recommendation still had to be withdrawn.
Randomised trials support it for migraine prevention. The American Academy of Neurology rated it favourably and then retracted that guidance — not because the trials collapsed, but because the plant contains hepatotoxic pyrrolizidine alkaloids and whether a given bottle contains them depends wholly on how it was made.
That is a different failure mode from anything else here. The problem is not that the herb does not work, and not that the plant is inherently unusable. It is that the safety of the product cannot be verified by the person taking it, and a regulator faced with that has essentially no option but to withdraw.
Nomenclature verified against GBIF backbone taxonomy.