The myth that comfrey is completely benign just won't die.
It's popped up again on a mailing list I'm on. A list member lamented the fact that the FDA (or suchlike) has banned the plant ... here's my reply.
That's because comfrey contains livertoxic pyrrolizidine alkaloids.
Which directly cause veno-occlusive liver disease.
Which is silent, until your liver is fried.
Comfrey (Symphytum officinale and other species) had been considered safe because the onset of liver problems is so slow that you couldn't really connect the disease to the plant. Also, they didn't do liver autopsies all that often, half a century and more ago. Nowadays, liver autopsies are a tad more common; in addition, there's the possibility of doing a liver biopsy - same as an autopsy, but on live people. Autopsies and biopsies do prove that yep, comfrey is toxic.
Comfrey has necessitated a handful of liver transplants over the last two or three decades. Those are the ones where comfrey was known to cause liver failure. There might be more, and of course, there might be a few deaths due to liver failure due to comfrey livertoxicity.
This toxicity of comfrey has been known since the mid 1980s. Any herbal people who still insist that it's completely benign don't know what they're talking about.
Another herb which contains livertoxic pyrrolizidine alkaloids is coltsfoot (Petasites hybridus and other species, and Tussilago farfara). Of these, Petasites has killed a baby, cos mom drank the tea for her cough ...
Stay away from all and any of the plants which contain livertoxic pyrrolizidine alkaloids, especially if you're pregnant or nursing.
The Germans are perhaps sanest about these toxic alkaloids, and suggest that you might drink Tussilago (but not Petasites) tea for a few weeks every year. You'll find their suggestions for European herbs here.
Note, there are also nontoxic pyrrolizidine alkaloids. Echinacea is an example of a plant which contains completely benign pyrrolizidine alkaloids.
Instead of comfrey, try calendula or plantago - both of these are extremely good tissue healers. Add one or the other high-silica mineral herb like horsetail or the green parts of oats to that, and you've pretty much emulated comfrey's healer + minerals qualities.
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