What are the side effects of garlic in the body?

November 8, 2025 •

4 min read

For centuries, garlic has been revered for its flavour and potential health benefits, yet it is not without its drawbacks. Understanding what are the side effects of garlic in the body is crucial for safe consumption, particularly when using supplements or consuming it in large quantities. While many of its adverse effects are mild, some are more serious, impacting individuals with specific health conditions.

Quick Summary

Garlic consumption can lead to digestive discomfort such as heartburn, gas, and bloating, particularly in sensitive individuals or when consumed raw. It can also increase bleeding risk due to its antiplatelet properties and cause bad breath, body odor, and allergic reactions affecting the skin and respiratory system.

Key Points

Digestive Issues: Garlic is high in fructans, which can cause gas, bloating, and abdominal pain in people with sensitive digestive systems or IBS.
Increased Bleeding Risk: Garlic has blood-thinning properties and can increase the risk of bleeding, especially when combined with blood-thinning medications or before surgery.
Aggravates Acid Reflux: Garlic can relax the lower esophageal sphincter, triggering or worsening symptoms of acid reflux and heartburn in susceptible individuals.
Causes Body Odor: The sulfur compound allyl methyl sulfide is not digested and is released through sweat glands and the lungs, causing persistent bad breath and body odor.
Allergic Reactions: Though rare, some people are allergic to garlic, experiencing symptoms ranging from skin rashes to severe anaphylaxis.
Skin Irritation: Applying raw garlic or its oil directly to the skin can cause contact dermatitis, burns, or blistering.

Digestive System Issues

Garlic is a high-FODMAP food due to its content of fructans, a type of carbohydrate that can be difficult for some people to digest. For individuals with Irritable Bowel Syndrome (IBS) or fructan intolerance, this can cause significant gastrointestinal discomfort. The fermentation of fructans in the colon by gut bacteria produces gas, leading to bloating, abdominal pain, and flatulence. Overconsumption of raw garlic on an empty stomach is a common trigger for these symptoms.

Aggravation of Acid Reflux

For those with Gastroesophageal Reflux Disease (GERD), garlic can be a significant trigger for heartburn and acid reflux. This happens because garlic can relax the lower esophageal sphincter, the muscle separating the stomach from the esophagus, allowing stomach acid to flow back up. The burning sensation and nausea associated with acid reflux are a common complaint from heavy garlic consumers. Cooking garlic may help mitigate this effect for some individuals.

Increased Risk of Bleeding

One of garlic's more serious side effects is its antiplatelet effect, which can inhibit the body’s ability to form blood clots. While this can be a benefit for cardiovascular health, it poses a significant risk for those with bleeding disorders or individuals taking blood-thinning medications, such as warfarin or aspirin. Excessive intake, especially from supplements, can amplify the effect of these medications, increasing the risk of bruising and uncontrolled bleeding. It is standard medical advice to stop taking garlic supplements at least two weeks before any scheduled surgery to minimize bleeding risk.

Allergic Reactions and Skin Irritation

Though less common, some people may have an allergy to garlic, with reactions ranging from mild to severe. Symptoms can include hives, skin rashes, itching, or swelling of the face, lips, and tongue. In rare, severe cases, an allergic reaction can lead to anaphylaxis, a life-threatening condition. Contact dermatitis can also occur from direct skin contact with raw garlic, with some reports of chemical burns and blisters from applying it topically.

Symptoms of Garlic Allergy

Mild: Skin rashes, tingling mouth, nasal congestion.
Moderate: Hives, itching, nausea, or vomiting.
Severe: Difficulty breathing, wheezing, swelling of the throat, or anaphylaxis.

Body Odour and Bad Breath

Garlic's distinctive scent is caused by several volatile sulfur compounds, most notably allyl methyl sulfide (AMS). When garlic is crushed or chopped, the compound alliin is converted into allicin, which is then metabolized into AMS in the body. AMS cannot be broken down and is released through sweat glands and the lungs, causing persistent bad breath and body odor that can last for hours or even days.

Potential Drug Interactions

Garlic supplements can interact with a variety of medications, altering their effectiveness or increasing side effects. This is particularly concerning for individuals with chronic health conditions. In addition to blood thinners, potential interactions include:

HIV/AIDS Medications: Some studies suggest that garlic can lower the blood levels of certain protease inhibitors, rendering them less effective.
Blood Pressure Medications: Since garlic can naturally lower blood pressure, combining it with antihypertensive drugs could cause blood pressure to drop too low.
Diabetes Medications: Garlic's blood sugar-lowering effects can be compounded by antidiabetes drugs, potentially leading to hypoglycemia.
Isoniazid: Garlic may reduce the body’s absorption of this medication used for treating tuberculosis.

Mitigating Side Effects of Garlic

For those who experience adverse effects but still want to enjoy garlic, there are several strategies that can help minimize discomfort:

Moderate Your Intake: Sticking to 1–2 cloves per day can provide flavour without triggering significant side effects.
Cooking vs. Raw: Cooking garlic can reduce the potency of the sulfur compounds, which lessens body odour and digestive irritation.
Use Alternatives: If you have a fructan intolerance, try garlic-infused oil, which provides the flavour without the problematic carbohydrates.
Counter Bad Breath: Consuming milk, parsley, or apples after eating garlic can help neutralize bad breath.
Consult a Doctor: If you are on medication or have underlying health conditions, always consult a healthcare provider before adding large amounts of garlic or garlic supplements to your diet. For specific guidance, the National Center for Complementary and Integrative Health provides resources on herbs and supplements, including garlic.

Side Effect Comparison: Raw vs. Cooked vs. Supplement


Side Effect	Raw Garlic	Cooked Garlic	Garlic Supplement	Source
Digestive Upset	High risk, especially on empty stomach	Lower risk, as heat denatures some compounds	Variable, depends on formulation and dosage	,,
Bad Breath/Body Odor	High risk due to potent sulfur compounds	Reduced risk, some compounds are broken down	Variable, often 'odorless' products exist	,
Bleeding Risk	Increased risk due to antiplatelet effect	Less studied, but may still pose a risk	Increased risk, especially with high doses	,
Heartburn/GERD	High risk, especially for those with GERD	Lower risk, but can still trigger symptoms	Variable, depends on formulation	,
Allergic Reaction	Can trigger allergic dermatitis upon contact	Less likely to trigger allergic reactions	May contain allergens, check ingredients	,

Conclusion

While garlic is celebrated for its flavour and potential health benefits, it's essential to be aware of its side effects. From common issues like digestive distress, bad breath, and body odour to more serious concerns such as increased bleeding risk and allergic reactions, the impact of garlic varies greatly among individuals. For most people, enjoying garlic in moderation is safe. However, those on blood thinners, with GERD, IBS, or a diagnosed garlic allergy should exercise caution and consult a healthcare provider. By understanding these potential risks, you can make informed decisions about your garlic consumption.

Frequently Asked Questions

Yes, garlic can cause heartburn, especially in those with Gastroesophageal Reflux Disease (GERD). It can relax the sphincter that prevents stomach acid from flowing back into the esophagus.

Yes, garlic possesses antiplatelet properties that can slow down blood clotting. This effect is amplified with large doses or when taken with blood-thinning medications.

The odour is caused by sulfur compounds like allyl methyl sulfide. These compounds are not fully digested and are released through the breath and sweat glands, causing a strong, lingering scent.

Individuals on blood thinners, those with GERD or IBS, and people with a known garlic allergy should be cautious or avoid excessive intake. Pregnant women should also stick to food amounts rather than medicinal doses.

Yes, raw garlic is more potent and tends to cause more side effects, including digestive upset and bad breath, because its heat-sensitive compounds are more active.

Yes, garlic supplements can cause side effects similar to consuming large amounts of garlic, including digestive issues and an increased risk of bleeding.

Yes, applying raw garlic or its oil directly to the skin can cause contact dermatitis and chemical burns, sometimes severe enough to cause blisters.