What are the side effects associated with using oregano essential oil?

Oregano oil is likely safe for use in healthy adults, but it may produce mild side effects such as upset stomach. People allergic to plants in the Lamiaceae family may have an allergic reaction. Oregano oil may not be safe for pregnant women and may cause miscarriage, according to WebMD.

Oregano essential oil may act like a diuretic. It might also decrease how well the body gets rid of lithium, which could result in serious side effects. If you are taking lithium, you must talk with your doctor before taking oregano. Oregano oil, taken three times daily for six weeks, can be effective in treating intestinal parasites, explains WebMD.