Garlic has been used as a spice and an herbal remedy for thousands of years, according to the University of Maryland Medical Center. Garlic is full of antioxidants that help eliminate free radicals, which are waste products created in the body during conversion of food to energy. These particles damage cells and contribute to disease. Antioxidant-rich garlic supplements may boost the immune system and help prevent heart disease, high cholesterol, high blood pressure and cancer. Garlic supplements are available in many forms, including whole fresh garlic and garlic capsules, oil and extracts. Although the UMMC notes that garlic has low toxicity, it can cause some side effects.
Gastrointestinal Side Effects
The most common side effects of garlic supplements are gastrointestinal, as noted by the Physicians' Desktop Reference. They can include lack of appetite, upset stomach, bloating, nausea, vomiting and diarrhea. Garlic also can cause bad breath and unpleasant body odor.
Blood Thinning
Garlic has blood-thinning properties and may increase the risk of abnormal bleeding. Symptoms include unexplained bruising, bleeding gums, nosebleeds, or other unusual bleeding. The Physicians' Desktop Reference recommends discontinuing garlic supplements two weeks before having surgery or dental work to avoid the risk of increased bleeding. Garlic may also strengthen the effects of anticoagulant medications, according to the UMMC, as reports have been made of a possible interaction between garlic and the blood-thinning drug warfarin, which is commonly prescribed as the brand Coumadin. Medications with similar effects include clopidogrel, commonly prescribed as Plavix, and heparin, aspirin and ibuprofen.
Uncommon Side Effects
Other side effects associated with garlic supplements are less likely, according to the UMMC. They include dizziness, fatigue, headache, muscle aches and sweating. The Memorial Sloan-Kettering Cancer Center notes that garlic may lower blood sugar and lead to hypoglycemia, particularly in people taking medication to control diabetes. Signs of hypoglycemia include fatigue, headache, shakiness and problems concentrating. More serious cases, include symptoms of confusion, fainting and seizures, which are most commonly associated with diabetic medication lowering blood sugar too severely.
Allergic Reaction
As with any herbal supplement, some people may experience an allergic reaction to garlic, as noted by the Physicians' Desktop Reference. Signs include difficulty breathing, wheezing, chest tightness, itching, a rash or hives, tingling in the mouth or throat, and swelling of the face, throat or hands. Handling garlic may cause skin irritation and sores in people allergic to the substance.
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