The PA alkaloid test in mice that caused damage was a test that was done by giving the mice concentrated doses that were far greater than a human would get by just eating comfrey in moderation.
And the body weight of the mice compared to humans... tsk tsk. What a poor test. It was an over dose. Anyone can over dose on a good thing when eaten excessively. One would think the test was done to deliberately discredit the herb which has been used for thousands of years in Europe and the Celtic Isles.
Feeding comfrey to cattle, goats, rabbits, and sheep does not harm them either. (It will kill an iguana. First hand experience. Comfrey is in the spinach family)
OH YES!!!!
Another great use for comfrey!!
Bocking 14 makes an outstanding grassy border control. For some reason grass does not like mature comfrey. You can plant a border row of comfrey between your lawn and Perennial Gardens. It will keep the grass at bay. I put a row of comfrey on each side of my stone and brick walkway to prevent the lawn from invading my wall way.