Oregano (Origanum vulgare) leaves and oil contain carvacrol, thymol, eugenol and rosmarinic acid. Oregano has been used in medicinal doses for respiratory and gastrointestinal disorders and as an antimicrobial. Oregano oil has been advocated as a treatment for lactation-related Candida infection of the nipples;[1] however, no clinical studies have confirmed the safety or efficacy of this use. No data exist on the excretion of any components of oregano into breastmilk or on the safety and efficacy of oregano in nursing mothers or infants. Oregano and oregano oil are "generally recognized as safe" (GRAS) as food ingredients by the U.S. Food and Drug Administration. Oregano is generally well tolerated, but gastrointestinal upset and allergic skin reactions have been reported rarely. Because of a lack of data, oregano in amounts higher than those found in foods as a flavoring should probably be avoided during breastfeeding.
Dietary supplements do not require extensive pre-marketing approval from the U.S. Food and Drug Administration. Manufacturers are responsible to ensure the safety, but do not need to prove the safety and effectiveness of dietary supplements before they are marketed. Dietary supplements may contain multiple ingredients, and differences are often found between labeled and actual ingredients or their amounts. A manufacturer may contract with an independent organization to verify the quality of a product or its ingredients, but that does not certify the safety or effectiveness of a product. Because of the above issues, clinical testing results on one product may not be applicable to other products. More detailed information about dietary supplements is available elsewhere on the LactMed Web site.