Comfrey for back pain

thelostherbs.com/how-to-treat-back-pain-with-comfrey-root/

From the article: Comfrey’s strong roots draw up nutrients from the soil.  The roots of the comfrey plant contain chemical substances called allantoin and rosmarinic acid. Allantoin boosts the growth of new skin cells, while rosmarinic acid helps relieve pain and inflammation. Extracts are still made from the roots and leaves and turned into ointments, creams, or salves.

https://thegrownetwork.com/comfrey/

Comfrey is a powerful healing plant that is sometimes called the king of the vulneraries (healing plants). Unfortunately, comfrey bears a stigma. In the 1970s, scientists discovered the presence of pyrrolizidine alkaloids (PAs) in comfrey that could harm the liver. Panic spreads much faster than prudence or careful research, and soon comfrey had fallen out of favor. The medical community turned against comfrey. Some countries even banned its sale.

But long before comfrey was a scary plant, it was a healing plant of high esteem, used to treat a variety of ills.