What are the side effects of taking olive leaf extract?

October 17, 2025 •

3 min read

While olive leaf extract is generally considered safe for most people, some studies report mild side effects like stomach pains, headaches, and dizziness. Being aware of what are the side effects of taking olive leaf extract, including interactions with medications and contraindications, is crucial for safe supplementation.

Quick Summary

Taking olive leaf extract may cause mild side effects like stomach upset or headaches. A Herxheimer "die-off" reaction can also occur. The extract can interact with blood pressure and diabetes medications and should be avoided during pregnancy or if allergic.

Key Points

Mild Side Effects: Common mild side effects include stomach upset, headaches, and dizziness, which can often be managed by adjusting the dosage or taking with food.
Herxheimer Reaction: Some individuals may experience a "die-off" reaction with flu-like symptoms and fatigue as the body detoxifies. This is a temporary and often expected response to the extract's antimicrobial action.
Drug Interactions: Olive leaf extract can interact with medications for blood pressure and diabetes, potentially causing levels to drop too low. It may also interfere with blood thinners and certain chemotherapy drugs.
Contraindications: The extract should be avoided by pregnant or breastfeeding women due to insufficient safety data. Individuals with allergies to olive pollen or plants in the Oleaceae family should also use caution.
Importance of Medical Consultation: Always consult a healthcare provider before starting olive leaf extract, especially if you have underlying health conditions, are on medication, or are scheduled for surgery.
Starting Dosage: Beginning with a low dose and gradually increasing it can help the body adjust and minimize the occurrence of side effects, including the Herxheimer reaction.

Understanding the Safety Profile of Olive Leaf Extract

Olive leaf extract comes from the leaves of the olive tree (Olea europaea) and has a long history of traditional use. Its health benefits are primarily linked to the compound oleuropein. While generally well-tolerated, it is important to be aware of potential side effects and risks, especially since dietary supplements are not regulated by the FDA in the same way as prescription drugs. Side effects are usually mild, but caution is advised for individuals with existing health issues or allergies.

Mild but Manageable Side Effects

Many people experience only minor, temporary side effects as their body adjusts to olive leaf extract. Common issues include stomach pain, nausea, and diarrhea, particularly with high doses or when taken on an empty stomach. Taking the extract with food may help. Headaches and dizziness are also reported, potentially linked to a detoxifying effect. Less common effects include coughing, vertigo, and dry mouth. Staying hydrated can help with dry mouth. If symptoms persist, discontinue use and consult a healthcare professional.

The Herxheimer "Die-Off" Effect

For some users, particularly those taking olive leaf extract for its antimicrobial properties, symptoms may be due to a Herxheimer reaction. This reaction occurs when a large number of pathogens are rapidly killed, releasing toxins that trigger an immune response and a temporary increase in symptoms. Symptoms may include fatigue, flu-like symptoms, headaches, muscle aches, rashes, diarrhea, and joint aches. While uncomfortable, these symptoms often indicate the extract is working and usually subside within a few days. Starting with a low dose and gradually increasing it can help manage the intensity of this reaction.

Important Drug Interactions

Olive leaf extract can interact with certain medications, mainly those affecting blood pressure and blood sugar. Consult your doctor before using olive leaf extract if you are taking:

Blood Pressure Medications: The extract can lower blood pressure, potentially causing it to drop too low when combined with blood pressure drugs.
Diabetes Medications: Olive leaf extract can lower blood sugar, increasing the risk of hypoglycemia when taken with insulin or other diabetes medications.
Blood Thinners: The extract might have an anti-platelet effect, potentially increasing bleeding risk with anticoagulants like warfarin.
Chemotherapy Drugs: There's a potential for interference with certain chemotherapy treatments. Always consult your oncologist.

Who Should Avoid Olive Leaf Extract?

Certain individuals should avoid or use olive leaf extract with caution:

Pregnancy and Breastfeeding: Safety data is insufficient, so avoidance is generally recommended.
Allergies: Those allergic to olive trees or related plants (like jasmine) may have a reaction. Symptoms can include rash or swelling.
Individuals with Low Blood Pressure: The extract can lower blood pressure, potentially causing dizziness.
Kidney or Liver Conditions: Consult a doctor before use as high concentrations have been linked to liver issues in some animal studies.
Before Surgery: Stop taking at least two weeks prior to surgery due to potential effects on blood clotting and sugar.

Side Effect vs. Detox Reaction: A Comparison Table


Feature	Mild Side Effect	Herxheimer "Die-Off" Reaction
Cause	Initial bodily adjustment to the supplement, especially high doses.	Rapid release of toxins from dying pathogens (bacteria, fungi, etc.).
Onset	Usually begins within hours of the first dose.	Can start within hours or days of beginning supplementation.
Symptoms	Stomach upset, headache, dizziness, nausea.	Intense fatigue, flu-like symptoms, fever, body aches, rashes.
Duration	Typically temporary, lasting for a few days to a week.	Usually resolves within 24-48 hours but can last longer depending on the body's toxic load.
Management	Lowering the dose or taking with food.	Reducing the dose, staying hydrated, and supporting detoxification pathways.
Prognosis	Generally resolves completely without further issues.	Indicates the antimicrobial action is occurring, with symptoms subsiding as the body clears toxins.

Conclusion

While olive leaf extract has potential health benefits, it's important to be aware of potential risks. Most side effects are mild, but drug interactions and the possibility of a Herxheimer reaction necessitate caution. Always start with a low dose, take with food, and consult a healthcare professional, particularly if you have existing health conditions, are on medication, or have upcoming surgery. Medical guidance is crucial for safe use and managing adverse reactions, especially given that the FDA does not regulate dietary supplements and product quality can vary. Examine.com is a helpful resource for evidence-based supplement information.

Frequently Asked Questions

The most common side effects are mild gastrointestinal issues, including stomach pain, diarrhea, and nausea. Some people also report headaches and dizziness, especially when they first start taking the supplement.

Yes, a Herxheimer reaction, or "die-off" effect, can be caused by olive leaf extract. It is a temporary worsening of symptoms like fatigue, headaches, and flu-like symptoms as the body releases toxins from rapidly dying pathogens.

Individuals who are pregnant or breastfeeding, have allergies to olive trees, or have low blood pressure should avoid it. Additionally, those with diabetes, kidney or liver disease, and those on blood thinners or chemotherapy should seek medical advice first.

Yes, it can. Olive leaf extract has blood pressure-lowering properties and can have an additive effect when taken with blood pressure medication, potentially causing your blood pressure to drop too low.

The safety of olive leaf extract during pregnancy and lactation has not been sufficiently studied, so it is generally recommended to avoid it during these periods.

To minimize stomach upset, you can try starting with a lower dose and gradually increasing it. Taking the supplement with a meal or snack rather than on an empty stomach can also be helpful.

Yes. Olive leaf extract can lower blood sugar levels. If you are taking insulin or other medications for diabetes, combining them with the extract could increase your risk of hypoglycemia (low blood sugar).