Comfrey, known also as Knitbone, Knitback, Bruisewort, Boneset, as well as other names, clearly has been historically considered a valuable herb in healing. The roots and leaves contain allantoin, a protein that stimulate cell proliferation. It has been used for speeding the healing in broken bones, sprains, burns, sore joints, wounds, helping with dry skin, and reducing swelling in fractures.
Use fresh, clean Comfrey leaves in a poultice for external application, if you have access to it. You can also find Comfrey salves at health food stores or online. You may find Comfrey in large, tea-bag-like poultices, or in the dried bulk section, but you will not find any Comfrey tea bags, as it has been banned for internal use in the U.S. (But the SSRI drugs that induce people to shoot up schools and kill their whole family...those are still fine. Yeah.)
This Comfrey-phobia comes from studies done in the 1970's and 1980's done on rats, that indicated that Comfrey use can cause liver cancer and disease. The problem with these studies is that they were done on rats, which process poisons different than humans, they were done with high dosages, and in some cases, Comfrey itself was not used, but instead just the active compounds in Comfrey. Personally, I find these studies highly questionable, and I would not be the least bit surprised if I found out the studies were paid for by the drug companies. (You know, the people who say herbs are dangerous, but aspirin, which kills 5000 people a year, and causes internal bleeding and sub-arachnoid hemorrhaging, is perfectly safe. Yeah, you can trust those guys.)
So, while I would use caution in taking Comfrey internally, I personally don't think a little Comfrey tea once in a while is going to hurt me. But I am not a doctor, nor a scientist, so any use of Comfrey should be done with the advice of your licensed health care practitioner, and at your own risk.
It is generally considered to be safe to use topically, as it is said the alkaloids will not penetrate the skin. However, I would use caution in this as well, as the skin is the largest organ in your body...anything you put on your skin gets into your system. Never put anything on your skin whose bottle is labeled "not for internal use". Just my opinion. So my personal choice would be to use Comfrey topically when needed, on occasion.
I have used Comfrey in a poultice to treat what I believe was pink eye. My eye was starting to look inflamed and infected, overnight. I made a Comfrey tea bag, soaked it in just enough boiling water to soak the bag, but not float it, then squeezed out the excess liquid just until it wasn't dripping. I applied it close to my eye, but not close enough to get liquid in it (wasn't sure if that would be bad or not...you don't want to mess up your eyes). I don't know how long I kept it there, but at least ten minutes. My symptoms were gone the next day.
Comfrey has also been used as fertilizer. Since it has high levels of potash, it is perfect for tomato, cucumber, pepper, and potato plants. One of the links below can give you instructions on how to do that.
I hope this inspires you to consider planting Comfrey in your garden, or at least keeping a stock of dried Comfrey on hand. It is also a plant that grows in the wild, so if you learn to properly identify it, you can harvest wild Comfrey. For those into preparedness or self-sufficiency, Comfrey is a must.
Turning Comfrey into a natural fertilizer
Botanical info on Comfrey.
Safety of using Comfrey topically.
Information questioning the testing done on rats that led to the banning of internal use of Comfrey.
How to grow and preserve Comfrey.