Slippery elm & marshmellow root - do they inhibit absorption of other nutrients?
I have my hotheaded youngster on a few herbs to help with preventing ulcers and stomach upsets, slippery elm and marshmallow root being the two main ones, at small doses (not heaps of them). I've been told that they can both be fed long-term with no side effects or issues, but I was also told that they can both inhibit absorption of meds and supplements due to their coating effect. She definitely does better on them than off them, and the doses aren't exactly huge, but I don't want her to not be getting the other things she needs in her diet... any input?
That's the problem with herbal remedies--so many unanswered questions. You could go check out some of the more in-depth sites that have good compendia of herbal products. Johns Hopkins has one. Or a textbook of herbal pharmacology.
One thing to think about Slippery Elm (and all herbs): Different effects based on different parts of the plant.
For slippery elm the whole bark is an abortificant but the inner bark rind is a mucilage and has demulcent and emollient effects (hence it's use for cough). When it is ingested, this can cause reflex stimulation of the nerve endings in the GI tract leading to mucous secretion. This is the *theory* behind it's use as a protective agent for ulcers. When applied topically to the skin, the oleoresins in it can case contact dermatitis.
Because slippery elm is a mucilage agent, it can *in theory* prevent/decrease absorption of other orally administered medications or foodstuffs. This has barely been studied though, so who really knows. Usually when you want to avoid this kind of an interaction - you separate apart the timing of the medication with other things. So say mare eats at 9am and 4pm, give the supplement at 12pm and 8pm. The goal is to give them at a time when no other food is in that belly so it can't block absorption. The worst effect would be giving them all together (food, other meds + slippery elm).
Marshmallow is similar. The leaves and roots contain mucilage that can in *theory* protect mucous membranes from local irritation. As a side effect, marshmallow can lower blood glucose levels. It's usually studied given as a syrup or a tea made from dried root or leaf.
Similar agents that are actual prescription/OTC medications and therefore have been studied/tested would be sucralfate and sodium alginate (Gaviscon).
My references: Brink F. Herb Contraindications and Drug Interactions; German Commission E Monographs; Natural Medicine Comprehensive Database; PubMed for primary literature (open to the public - but may need a library to help access the actual articles if not free to public).
And remember - no herbal products are regulated in the US and so what you are getting vs. what the label SAYS you are getting could be entirely different.