"In 2001, the United States Food and Drug Administration issued a warning against internal usage of herbal products containing comfrey, and eventually banned Comfrey products intended for internal use. In addition to restrictions on oral use, scientists and medical professionals recommend applying Comfrey extracts no longer than 10 days in a row, and no more than 4–6 weeks a year," Wikipedia reads.
According to Richters.com, comfrey is a perennial that grows hardily in Zones 3 through 8. Indianapolis is in Zone 5B, so it will grow here. It is considered easy to germinate, and can be planted any time.
Dr. John Lust writes in The Herb Book that comfrey is also known as blackwort, bruiseword, gum plant, healing herb, knitback, salsify, slippery root and wallwort.
According to Lust, comfrey can relieve pain, slow discharges, sooth irritated mucous membranes, relax the skin, serve as an expectorant, stop bleeding, reduce fever and promote the healing of wounds.
"Externally, use the powder as a hemostatic agent, and make a poultice for wounds, bruises, sores, and insect bites,' Lust writes. "The hot pulp of the rootstock makes a good external application for bronchitis, pleurisy, and for the pain and inflammation of pulled tendons. Add the rootstock to your bath water regularly for a more youthful skin."
A German study touts comfrey's effectiveness.
"Comfrey root extract has been used for the topical treatment of painful muscle and joint complaints," the study reads. "It is clinically proven to relieve pain, inflammation and swelling of muscles and joints in the case of degenerative arthritis, acute myalgia in the back, sprains, contusions and strains after sports injuries and accidents."