it may depend on the area you live in, but I recall hearing one time that comfrey was pretty much a "banned" plant out here in the PNW. meaning, you can't buy the comfrey plant anymore. I think it has something to do with the toxicity that it can pose if eaten. When I had a community pea-patch garden in Seattle, there was a bunch of growing wild in that general area and I would often cut it, dry the leaves and make a tea. My FIL swore by its healing properties for cancer that he had at one point and then the cancer disappeared. He credits drinking comfrey tea. I would love to grow some but the only way I think I'll be able to is if I find some growing someplace and dig some of it up. It does spread like crazy so most people that do have some growing are more than happy to pull out a few plants for transplanting.