Vervain supplies variable quantities of vitamin K and can lessen the effect of oral anticoagulant therapy.

– Oral anticoagulants and medicinal plants. An emerging interaction — Argento A, Tiraferri E, Marzaloni M. — Ann Ital Med Int. 2000 Apr;15(2):139-43.

Vervain can reduce iron absorption.
– Br J Nutr 1999 Apr;81(4):289-95 — Inhibition of non-haem iron absorption in man by polyphenolic-containing beverages. — Hurrell RF, Reddy M, Cook JD.

May cause allergic skin reactions.

– Contact Dermatitis 1994 Sep;31(3):200-1 — Allergic contact dermatitis from Verbena officinalis L. — Del Pozo MD, Gastaminza G, Navarro JA, Munoz D, Fernandez E, Fernandez de Corres L.

Should not be taken during pregnancy unless it is recommended by a herbalist and your physician.


– McGuffin M, Hobbs C, Upton R, Goldberg A (eds). — American Herbal Products Association’s Botanical Safety Handbook. Boca Raton, FL: CRC Press, 1997.