Equisetum Arvense
Equisetum arvense (field horsetail) has been used in traditional medicine but contains thiaminase activity that can degrade vitamin B1, leading to thiamin deficiency with chronic high consumption, and potentially toxic alkaloids (palustrine). Confusion with related toxic Equisetum species (E.
What it is
Field horsetail, a perennial fern-allied plant; aerial parts contain silica, flavonoids, and alkaloids.
Traditional herbal supplement, source of silica.
Why it's flagged
- thiaminase activity (vitamin B1 deficiency)
- potential nicotine/palustrine alkaloids in misidentified species
- contraindicated in pregnancy/lactation
What regulators actually say
"Equisetum arvense has thiaminase activity that may degrade thiamine; clinical relevance is most documented in livestock but caution is advised for chronic human use."
"Horsetail (Equisetum arvense) supplements have been associated with rare cases of liver injury and may contain thiaminase, causing vitamin B1 deficiency."
Regulatory status
United States — FDA
Used in dietary supplements; not a regulated additive; FDA has issued advisories on adulterated horsetail products.
European Union — EFSA
Traditional herbal medicinal product per EMA HMPC monograph; not a food additive.
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