To aid the healing of a broken bone, a window would need to be left in the cast near the fracture site, and comfrey applied. However, this is not always possible. Due to variations in pyrrolizidine alkaloid content, root preparations are unsafe for internal use unless they are guaranteed pyrrolizidine-free. Tea made from the leaf can generally be used safely for as long as a month. 6 Three cups per day can be drunk.
Comfrey contains potentially dangerous compounds known as pyrrolizidine alkaloids.
The roots contain higher levels of these compounds, and mature leaves contain very little if any of these alkaloids. 10 One study found that twenty-nine persons who had consumed comfrey from one to twenty years developed no sign of liver disease. Nevertheless, several reports of individuals who developed liver disease or other serious problems from taking capsules or tea of comfrey have been reported over the years. Because there is usually no indication on comfrey products whether they contain pyrrolizidine alkaloids, it is best to avoid internal use of products made from the root and to use products made from the mature leaf for no more than one month consecutively. Topical use of root or leaf is safe unless applied over broken skin, in which case comfrey should be used for no more than three days consecutively.