There are a number of cases of liver damage from taking Comfrey. This isn’t a theoretical issue. Some people died. Some people had liver failure.
Can you use Comfrey internally responsibly for certain issues? Probably, depending on the person, the problem, the dosage, the length of time taken, the dosage form, preexisting conditions and more.
Should it be used daily for prevention or general health? The potential for harm exist. The disease it causes is hard to identify and probably under-reported. So I believe no, you shouldn’t use it daily or long term.
I have many more thoughts on Comfrey that I’ll be writing to accompany the studies. For now, it seems like access to the full text of studies on Comfrey are more important. So here you go.
Symphytum uplandicum
PAs in plants including multiple species of comfrey
Symphytum officinale
Determination of Pyrrolizidine Alkaloids in Commercial Comfrey Products Analysis of herbal teas made from the leaves of comfrey
Analysis of herbal teas made from the leaves of comfrey
Diversity of Pyrrolizidine Alkaloids in the Boraginaceae
Comfrey Toxicity Revisted Rhode
Pyrrolizidine alkaloids in human diet
Pyrrolizidine alkaloids in medicinal plants from North America
Veno-occlusive Disease
Veno-occlusive disease of the liver from Comfrey case report
Hepatic Veno-Occlusive Disease
Comfrey Tea vs Purified PA’s in chicks
The comparative toxicity of a reduced, crude comfrey vs pure alkaloid in chicks
Paul Bergner’s Excellent Review of Comfrey
This list of articles isn’t comprehensive, but I’m working on adding more. If you have any journal articles on Comfrey that I’ve not included, or any request for full text articles on PA’s and Comfrey, please shoot me an email: eclecticherbalist at gmail