1. Studies pointing to harmful effects of Symphytum officinale were performed with the root which has a higher Pyrrolizidine alkaloid content and is not used internally in Dr. Christopher formulas.
J Pharm. Sci 1994 May;83 (5):649-53
Determination of pyrrolizidine alkaloids in commercial comfrey products demonstrates that products containing comfrey leaf in combination with other herbs contained the lowest alkaloid levels (0.1 ppm) of the products tested.
The leaves have the lowest alkaloid content of the plant parts tested. The leaf is the part used internally in Dr. Christopher's herbal combinations.
Gastroenterology 1985 Apr;88(4):1050-4
Hepatic venocclusive disease associated with the consumption of pyrrolizidine-containing dietary supplements.
The case discussed in this article described a 49 year old woman who ingested large amounts of Symphytum officinale root over a long period of time.
In this case the woman ingested large portions of the root for an extended period of time. The root is not used internally in Dr. Christopher's herbal combinations.
J Appl Toxicol 1983 Jun;3(3):127-30
Mutagenic effects of aqueous extracts of Symphytum officinale L. and of its alkaloidal factions.
This study was done on alkaloidal factions obtained from infusions of Symphytum officinale L. root and not the leaf. It shows that isolated constituents of the root may be toxic but fails to demonstrate the root is toxic in its whole form
This study shows that isolated constituents of the root can be toxic but fails to implicate the leaf which is used in Dr. Christopher's herbal combinations.
Experientia 1982 Sep 15;38(9):1085-7
Pyrrolizidine alkaloids from Symphytum officinale L. and their percutaneous absorption in rats.
This study demonstrates that pyrrolizidine alkaloids are not readily absorbed through the skin and therefore, are not of significant concern when applied in this manner.
The alkaloids in comfrey are not readily absorbed through the skin, external application of a crude preparation (cream or ointment of the whole plant) of the root is not harmful.