Reply To: Materia Medica
Hi Fara,
Thank you for asking this question as it’s in relation to understanding why something is ‘toxic’ and in what way. This can be an important aspect in working with botanical medicine.
In the case of comfrey the plant contains an alkaloid called pyrrolizidine alkaloid or you may see it written as ‘PA’ in short form. There are quite a few plants that contain PA’s ranging form echinacea, to borage to comfrey to coltsfoot. The level of toxicity is dependent on the type/structure of the PA, what type of herbal preparation you are using, for how long you are working with them and how it is administered.
In the case of comfrey, the leaves and roots have the toxic unsaturated PA’s, that if taken internally over a long period of time or at any high dose will lead to veno-occlusive liver disease. If someone has pre-existing liver disease then they should avoid comfrey internally all together. Oil infusions of comfrey do not extract any appreciable level of PA’s, so comfrey oil is a very safe way to work with comfrey topically. If someone is in need of a strong application of comfrey topically and needs to utilise a poultice, this is also considered safe, especially if it’s only over the course of a few days to help heal an acute injury (like strain or sprain). The amount of PA’s that would reach the liver if used as a poultice over a short period of time would not generally be anything to worry about. If this person has pre-existing liver disease and you/they want to be very cautious, then there are other plants that can support them and come with no concern at all.
Here’s a great blog post written by Sajah Popham of The School of Evolutionary Herbalism, where he clearly outlines PA’s, the different types and some plants that contain them. It’s a very clear and easy to understand reference point: https://www.evolutionaryherbalism.com/2024/05/22/the-truth-about-pyrrolizidine-alkaloids/
All the best,
Benna