There are no known drug interactions with Origanum vulgare, and it has been noted that it is compatible with other natural remedies and prescription drugs (Wild Oil of Oregano, 2010). However it is possible that individuals who use oregano may present with allergies. For individuals with sensitive skin, direct application of oil of oregano to the skin can cause irritation and/or rash (Joy of the Mountain Oil, 2010).
Furthermore, many manufacturers of oil of oregano caution, that due to its potency in concentrated form, oil of oregano should be diluted as instructed by the label when applying to sensitive or mucosal areas (Joy of the Mountain Oil, 2010). For example the Joy of the Mountain Oil of Oregano brand recommends a 1:2, 1:3 or 1:4 dilution with olive oil when applying oil of oregano to genital areas or inside the nostrils. Manufacturers also caution that infants under 6 months and pregnant or nursing mothers should not use oil of oregano, both orally and applied externally (Joy of the Mountain Oil, 2010).