What is the Side Effect of Garlic?

January 1, 2026 •

4 min read

While celebrated for its robust flavor and medicinal properties for centuries, garlic can produce unwanted reactions for some individuals. These side effects range from unpleasant but common issues like bad breath to more serious concerns like allergic reactions and potential interactions with medication.

Quick Summary

Garlic can cause common side effects such as bad breath, body odor, and digestive issues like heartburn, bloating, and gas, especially when consumed raw or in large quantities. More serious but less common side effects include allergic reactions and increased risk of bleeding, particularly for those on blood-thinning medications or with existing bleeding disorders.

Key Points

Bad Breath & Body Odor: The most common side effect is a lingering odor on the breath and skin caused by sulfur compounds released during digestion.
Digestive Issues: Raw garlic can cause heartburn, gas, bloating, and diarrhea, especially for those with sensitive digestive systems or IBS, due to its fructan content.
Increased Bleeding Risk: High doses of garlic, particularly supplements, can increase bleeding risk by inhibiting blood clot formation, which is a concern for people on blood-thinning medications.
Allergic Reactions: Though rare, some people can experience allergies ranging from contact dermatitis from handling raw garlic to systemic reactions like hives, asthma, and, in rare cases, anaphylaxis.
Drug Interactions: Garlic supplements can interfere with medications for blood thinning, HIV/AIDS, high blood pressure, and diabetes, potentially causing adverse effects.
Moderation is Key: Eating 1–2 cloves of garlic daily is generally considered safe and healthy for most, but excessive consumption increases the likelihood of experiencing negative side effects.

Common Side Effects of Garlic Consumption

For most people, the side effects of garlic are mild and related to its pungent, sulfur-containing compounds. These issues are more pronounced with raw garlic consumption.

Bad Breath and Body Odor

One of the most well-known side effects is bad breath, or halitosis. This is caused by volatile sulfur compounds, such as allyl methyl sulfide (AMS), which are released during digestion. AMS is absorbed into the bloodstream and then excreted through the lungs and skin pores, leading to a persistent odor that can linger for hours. This process also contributes to body odor.

Digestive Issues

Garlic is rich in fructans, a type of carbohydrate that can be difficult for some people to digest. For individuals with a fructan intolerance or Irritable Bowel Syndrome (IBS), consuming garlic can lead to digestive discomfort.

Bloating and Gas: Fermentation of undigested fructans by gut bacteria produces gas, causing bloating and discomfort.
Heartburn and Acid Reflux: Garlic may relax the lower esophageal sphincter (LES), the muscle that prevents stomach acid from flowing back into the esophagus. This can trigger or worsen symptoms of acid reflux and heartburn.
Nausea and Diarrhea: Consuming large amounts of raw garlic can irritate the digestive tract, potentially leading to nausea, vomiting, or diarrhea.

Serious Side Effects and Health Risks

While less common, some individuals may experience more significant side effects that require medical attention.

Increased Bleeding Risk

Garlic possesses antiplatelet properties, meaning it can inhibit blood clot formation. This effect is typically mild with regular culinary use, but concentrated garlic supplements can increase the risk of bleeding. This is particularly concerning for individuals on blood-thinning medications like warfarin, aspirin, or clopidogrel, as the combination can lead to excessive bruising and bleeding. It is also advised to stop taking high-dose garlic supplements at least two weeks before any scheduled surgery.

Allergic Reactions

Although rare, garlic can cause allergic reactions in some people. As a member of the allium family, cross-reactivity with other plants like onions and chives is possible. Symptoms of a garlic allergy can range from mild skin irritations to severe, life-threatening reactions.

Skin Reactions: Handling raw garlic can cause contact dermatitis, leading to skin rashes, blisters, or a burning sensation. The chemical diallyl disulfide is often responsible for this irritation.
Systemic Allergies: Ingestion can trigger symptoms such as hives, itching, nasal congestion, and asthma. In severe cases, anaphylaxis may occur, which is a medical emergency requiring immediate attention.

Interactions with Medications

Garlic supplements can interact with several types of medications by altering their effectiveness or increasing side effects.

Blood Thinners: As mentioned, garlic increases the risk of bleeding when taken with anticoagulant and antiplatelet drugs.
HIV/AIDS Medications: Garlic can decrease the absorption of certain protease inhibitors, such as saquinavir, potentially reducing their effectiveness.
High Blood Pressure Medications: Garlic may add to the effect of antihypertensive drugs, potentially causing blood pressure to drop too low.
Diabetes Medications: Garlic's blood-sugar-lowering effect can compound with diabetes medications, risking hypoglycemia (low blood sugar).
Tacrolimus: Garlic may interfere with the liver's metabolism of this organ rejection medication, potentially increasing its levels and causing liver damage.

Raw Garlic vs. Cooked Garlic Side Effects

There are notable differences in side effect intensity depending on whether garlic is consumed raw or cooked. Cooking helps to reduce some of the sulfur compounds, which can alleviate certain symptoms.


Feature	Raw Garlic	Cooked Garlic
Pungency/Odor	Stronger and more pungent due to higher allicin and sulfur compound content.	Milder, less intense aroma and flavor as heat breaks down some compounds.
Digestive Impact	More likely to cause heartburn, acid reflux, and general irritation, especially on an empty stomach.	Generally gentler on the digestive system, reducing the likelihood of issues for sensitive individuals.
Blood Thinning	May have a stronger antiplatelet effect, particularly in high doses.	The blood-thinning effect is less pronounced compared to raw garlic or supplements.
Allergenicity	More likely to cause contact dermatitis upon handling due to higher concentration of irritants.	Cooking reduces the allergenic potential, though cross-reactivity can still occur for highly sensitive individuals.

When to Reduce or Avoid Garlic

If you experience any of the adverse effects mentioned, consider moderating your garlic intake. Individuals with a garlic allergy should avoid it completely. If you are on medication, particularly blood thinners, or are preparing for surgery, consult your healthcare provider before taking garlic supplements. For those with digestive sensitivities, enjoying garlic in moderation and in its cooked form may help reduce symptoms.

Conclusion

While garlic is a potent and healthy addition to most diets, being aware of its potential side effects is crucial for certain individuals. From the common issues of breath and body odor to more serious risks involving digestive distress, bleeding, allergies, and drug interactions, the impact of garlic can vary significantly depending on the form, quantity, and a person's individual health status. By understanding these potential reactions and consulting a healthcare professional when necessary, you can safely continue to incorporate this flavorful ingredient into your life. For more detailed information on drug interactions, please consult a reputable medical source such as Drugs.com.

Frequently Asked Questions

Garlic contains sulfur compounds that are absorbed into the bloodstream during digestion and are then released through the lungs, causing a distinct, persistent odor on the breath.

Yes, a garlic intolerance is different from an allergy. Intolerance involves digestive system issues like gas and bloating due to difficulties processing fructans, while a garlic allergy is an immune system response with symptoms like hives or wheezing.

Cooking garlic can help reduce some of its potency and minimize certain side effects like heartburn and digestive irritation, but it does not eliminate them entirely. The fructans that cause issues for some people can remain even after cooking.

If you are on blood-thinning medication, it is critical to consult your doctor before significantly increasing your garlic intake or starting garlic supplements. Normal culinary amounts are generally safe, but high doses can increase bleeding risk.

Contact dermatitis is a skin irritation caused by handling raw garlic. It can result in rashes, blisters, or a burning sensation and is often caused by the chemical diallyl disulfide found in the allium family.

For people with naturally low blood pressure or those taking antihypertensive medications, high doses of garlic, especially supplements, could potentially cause blood pressure to drop too low. This requires careful monitoring.

There is no official guideline, but studies suggest that 1–2 cloves per day can offer health benefits. Side effects become more likely with larger amounts, so it's best to consume in moderation and adjust if you notice any negative reactions.

Yes, garlic supplements can interact with a range of medications, including certain HIV/AIDS drugs, high blood pressure medications, diabetes treatments, and immunosuppressants like tacrolimus.