Oregano is an herb related to lavender, sage, marjoram, thyme, basil, and mint. The dry leaves can be made into an oil, which is sold in two different forms: oil of oregano — which can be taken orally, as a supplement — and oregano essential oil, which may be diluted and applied topically. People use oregano to help treat acne, ringworm, stomach problem, and lung disorders, as well as taking it daily for prevention. Though generally considered safe for most in small doses, there are some possible side effects of using oregano essential oil or oil of oregano.


Most people who use oil of oregano do not experience a laxative effect, but some might develop diarrhea, specifically if they have an allergy to a plant in the mint family. Antidiarrheal medications can quickly help relieve these symptoms. If the side effect persists through multiple uses of oil of oregano, it is best to find an alternative or speak to a doctor.

man with diarrhea running to bathroom



Oil of oregano may also cause indigestion. Anyone taking this supplement should ensure it is properly diluted and that they are not ingesting an essential oil by mistake. To combat indigestion and other GI symptoms, drink a mixture of water and baking soda to neutralize the stomach. As with diarrhea, if this symptom continues, stop using oil of oregano.

woman with stomach pain sitting on bed



Another possible oregano oil side effect is nausea. This is usually caused by thymol, a natural plant chemical found in oregano and other herbs. In high doses, it can be an irritant, which affects the internal organs. Avoid taking oil of oregano on an empty stomach, and discontinue its use if nausea persists.

man with digestion trouble standing in bathroom



Along with nausea, thymol or other substances in oil of oregano might cause vomiting. Prolonged vomiting can lead to dehydration, so drinking plenty of fluids after will help you feel better faster. If you continue to vomit for more than a day, see a doctor.

sick woman kneeling over toilet



Some people experience an allergic reaction or various allergy symptoms when using oregano oil, either topically or orally. This is especially true for people allergic to other plants in the mint family. If a person knows they are allergic to oregano, they should not use oil of oregano or oregano essential oil. Speak to a doctor before using the supplement if you have a similar allergy.

older man scratching a rash on his arm



Oregano oil may affect how the blood clots . This means it is not recommended for people who have an increased risk of bleeding. Generally, doctors will require patients to stop using oil of oregano at least two weeks before a surgical procedure. Increased bruising may also occur as an oregano oil side effect. This is especially common in people taking anticoagulant drugs.

blood test concept with coagulation label on test tube


Low Blood Sugar

Another possible side effect of taking oil of oregano is low blood sugar or hypoglycemia, especially in people with diabetes. Anyone with blood sugar issues should speak to a doctor before beginning to take oil of oregano.

cropped image of person checking their blood sugar level


Reduced Lithium Removal

People taking lithium should not use oregano oil because it slows the removal of lithium from the body. This can have serious side effects including tremors, difficulty walking, and kidney problems. Always check with a doctor before taking new supplements if you are on any medication.

lithium questionnaire concept yes or no


Pregnancy Loss

Pregnant women should never take oil of oregano because it can negatively impact the baby. In rare instances, it could  lead to a miscarriage. Women who are breastfeeding should also refrain from using oregano oil. If you experience any spotting, call your gynecologist immediately.

pregnant woman with her hands on her belly


Drug Interaction

People who take medications or other supplements should take care if using oil of oregano orally. It can interact with antidiabetic drugs and anticoagulants, as well as copper, iron, and zinc absorption. It is important to discuss any new supplements with a doctor when someone has a pre-existing condition or is taking other medications.

older man reading his prescription bottles


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