Related Terms

• Allicepin, allicin, alliin, Allium cepa, Allium cepa L., allium vegetables, allylsulfides, apigenin, anthocyanins, botanicals, caffeic acid, cinnamic acids, cycloalliin, cysteine, diallyl disulfide, dipropyl disulfide, green onion, isoquercetin, isorhamnetin, kaempferol, L-cysteine sulfoxide, lignans, Liliaceae (family), luteolin, myricetin, onion extract, onion juice, onion powder, onion vinegar, organosulfur compounds, p-hydroxybenzoic acid, phytoestrogens, pickling onions, protocatechuic acid, quercetin, quercetin diglucoside, quercetin monoglucoside, red onion, rutin, S-alk(en)yl cysteine sulfoxides, S-allylcysteine, selenium, Spring Sweet, Sweet Imperial, syn-propanethial-S-oxide, taxifolin, Texas Grano 438, thiosulfinates (allyl methyl trisulfide, diallyl sulfide), Ultra Hybrid, vanillic acid, Vidalia onions, Walla Walla, white onion.

• Note: Onion (Allium cepa) should not be confused with plants of the Zigadenus species.

Background

• Onion (Allium cepa L.) is widely used around the world as a food product and has also been used for medicinal applications.

• Most of the available research has focused on scar prevention, but the results are mixed in this area. Onion has been used in the treatment of diabetes, cancer, heart disease, and alopecia areata (hair loss).

• As onion is a commonly consumed food, it is considered likely safe in smaller amounts, although there are reports of skin rash and gastrointestinal problems in sensitive individuals.

Scientific Evidence

Tradition/Theory

The below uses are based on tradition or scientific theories. They often have not been thoroughly tested in humans, and safety and effectiveness have not always been proven. Some of these conditions are potentially serious and should be evaluated by a qualified health care professional.

• Aging, anthelmintic, antibacterial, antifungal, anti-inflammatory, antimicrobial, antimutagenic, antioxidant, antiparasitic, antiplatelet (blood thinning), antiseptic, antiviral, arthritis, asthma, atherosclerosis (hardening of the arteries), baldness, bee stings, behavior (animal), benign prostatic hypertrophy (BPH), cataract, chilblains (inflammation of the hands and feet caused by exposure to cold and moisture), conjunctivitis, convulsions, coronary heart disease, cough, depression, diabetic nephropathy, digestion (prebiotic), digestive stimulant, exercise recovery, eye diseases (loa loa), eye inflammation, food preservative, gastrointestinal disorders, gout, hemophilia, immune enhancement, influenza, insecticidal, insomnia, irritable bowel syndrome (IBS), kidney dysfunction, leukemia, lice, liver protection, malaria, memory enhancement, neonatal disorders (asphyxia), neurodegenerative disorders, neuroprotection, obesity, osteoporosis, prostate conditions, scurvy, sinusitis, soft tissue injury (torn ligaments and tendons), sore throat, spermatogenesis, sun protection, tardive dyskinesia, thrombosis (blood clot), thyroid disorders, wound healing, wounds (stingray), yeast infections.

Dosing

The below doses are based on scientific research, publications, traditional use, or expert opinion. Many herbs and supplements have not been thoroughly tested, and safety and effectiveness may not be proven. Brands may be made differently, with variable ingredients, even within the same brand. The below doses may not apply to all products. You should read product labels, and discuss doses with a qualified healthcare provider before starting therapy.

Adults (over 18 years old)

• There is currently no proven effective medicinal dose of onion in adults.

• For diabetes, a diet supplemented with 20 grams of fresh onion three times daily has been taken by mouth.

• For high blood pressure, four onion-olive oil maceration capsules have been taken by mouth daily for one week.

• For scars, the following has been used: Mederma® (Merz Pharmaceuticals, Greensboro, NC, USA) applied to the skin three times daily for eight weeks; an onion gel extract applied to the skin three times daily for one month or for 10 weeks; Contractubex® gel (10% onion extract, 50IU of sodium heparin per gram of gel, and 1% allantoin) rubbed into scars 1-4 times daily for up to six months.

• For alopecia areata, Australian brown onion juice has been applied to areas of hair loss twice daily for two months.

• For determination of allergies, onion juice solution in 45% ethanol has been injected into the skin followed by an undiluted onion solution being applied to the skin at the injection sites.

Children (under 18 years old)

• There is currently no proven safe or effective medicinal dose of onion in children.

• For scars, Contractubex® gel (10% onion extract, 50IU of sodium heparin per gram of gel, and 1% allantoin) has been rubbed into scars 1-4 times daily for up to six months.

Safety

The U.S. Food and Drug Administration does not strictly regulate herbs and supplements. There is no guarantee of strength, purity or safety of products, and effects may vary. You should always read product labels. If you have a medical condition, or are taking other drugs, herbs, or supplements, you should speak with a qualified healthcare provider before starting a new therapy. Consult a healthcare provider immediately if you experience side effects.

Allergies

• Avoid in individuals with a known allergy or hypersensitivity to onion (Allium cepa) or its constituents. In some individuals, handling onion bulbs has caused skin rash, painful tingling in the fingers, or a reddening of the skin.

Side Effects and Warnings

• Onion is likely safe when consumed in food amounts and when onion extract is applied to the skin for scar healing.

• The primary adverse effects associated with onion are dermatologic (pemphigus, a chronic blistering disease, and skin rash) and gastrointestinal (heartburn, dyspepsia (upset stomach), gastric acidity, and gastroesophageal reflux). Swelling and ulceration of the eye have been reported from handling onion. Bronchial asthma from onion has been reported in children. Large amounts of onion may have toxic effects. Some studies have demonstrated contamination of onion with antibiotics, heavy metals, and microbes.

• Onion should be used cautiously in patients with hematologic (blood) disorders or taking anticoagulants or antiplatelets (blood thinners), in patients with diabetes or hypoglycemia (high or low blood sugar) or taking agents that affect blood sugar, and in patients with hypotension (low blood pressure) or taking agents that lower blood pressure. In clinical studies, onion has been found to lower blood pressure in both patients with and without hypertension (high blood pressure).

• Use cautiously in patients with gastrointestinal disorders as onion may worsen some conditions.

• Use cautiously in patients with high cholesterol since although most studies suggest that onion may have favorable effects on cholesterol levels, some studies have found that onion may increase cholesterol.

• Use cautiously in patients with or prone to cancer, since in limited study onion was associated with an increased risk of colon and stomach cancer.

• Onion may interfere with the way the body processes certain drugs using the liver's "cytochrome P450" enzyme system. As a result, the levels of these drugs may be decreased in the blood, and reduce the intended effects. Patients taking any medications should check the package insert and speak with a qualified healthcare professional, including a pharmacist, about possible interactions.

• Use cautiously with p-glycoprotein substrates or cyclosporine.

• Avoid in patients who are allergic or hypersensitive to onion or plants in the Lilaceae family. Anaphylaxis has been reported in sensitive individuals. Work-related allergy has been reported.

• Avoid if pregnant or breastfeeding in medicinal doses.

Pregnancy and Breastfeeding

• Onion, in medicinal amounts, is not recommended in pregnant or breastfeeding women due to a lack of available scientific evidence.

Interactions

Most herbs and supplements have not been thoroughly tested for interactions with other herbs, supplements, drugs, or foods. The interactions listed below are based on reports in scientific publications, laboratory experiments, or traditional use. You should always read product labels. If you have a medical condition, or are taking other drugs, herbs, or supplements, you should speak with a qualified healthcare provider before starting a new therapy.

Interactions with Drugs

• Cepae extract from onions, heparin, and allantoin may improve healing of injuries incurred during laser tattoo removal or surgery.

• Meals including onion have induced heartburn, dyspepsia (upset stomach), gastric acidity, and gastroesophageal reflux in clinical trials. Use onion cautiously with antacids.

• Allium plants, such as onion, may have antibiotic effects, and may have additive effects when used with other antibiotics.

• Onion may increase the risk of bleeding when taken with drugs that increase the risk of bleeding. Some examples include aspirin, anticoagulants ("blood thinners") such as warfarin (Coumadin®) or heparin, anti-platelet drugs such as clopidogrel (Plavix®), and non-steroidal anti-inflammatory drugs (NSAIDS) such as ibuprofen (Motrin®, Advil®) or naproxen (Naprosyn®, Aleve®).

• Onion may lower blood sugar. Caution is advised in patients with diabetes (high blood sugar) or hypoglycemia (low blood sugar), and in those taking drugs that affect blood sugar. Serum glucose levels may need to be monitored by a qualified healthcare professional, including a pharmacist, and medication adjustments may be necessary.

• Onion and onion essential oil may prevent fat-induced increases in serum cholesterol. Use cautiously with cholesterol-lowering medications.

• Onion or onion extract may have anticancer effects. Use cautiously when taken with medications to prevent or treat cancer.

• Onion may lower blood pressure; use cautiously with blood pressure medications.

• Onion may inhibit bone resorption; use cautiously with osteoporosis agents.

• Onion may interfere with the way the body processes certain drugs using the liver's "cytochrome P450" enzyme system. As a result, the levels of these drugs may be increased or decreased in the blood, and may cause increased or decreased effects or potentially serious adverse reactions. Patients using any medications should check the package insert, and speak with a qualified healthcare professional, including a pharmacist, about possible interactions.

• Onion may also interact with allopurinol, antidepressants, antifungals, anti-inflammatory agents, hormonal agents, nicotine, p-glycoprotein-regulated agents, simvastatin, triamcinolone, and uridine diphasophate glucuronosyl transferase substrates.

Interactions with Herbs and Dietary Supplements

• Allium plants, such as onion, may have antibiotic effects, and may have additive effects when used with other antibiotic herbs.

• Onion may increase the risk of bleeding when taken with herbs and supplements that are believed to increase the risk of bleeding. Multiple cases of bleeding have been reported with the use of Ginkgo biloba, and fewer cases with garlic and saw palmetto.

• Onion may lower blood sugar. Caution is advised in patients with diabetes or hypoglycemia, and in those taking herbs or supplements that affect blood sugar. Serum glucose levels may need to be monitored by a qualified healthcare professional, including a pharmacist, and doses may need adjustment.

• Onion or onion extract may have anticancer effects. Use cautiously with herbs and supplements taken to prevent or treat cancer.

• Onion and onion essential oil may prevent fat-induced increases in serum cholesterol; use cautiously with herbs and supplements taken for cholesterol.

• Onion may decrease systolic and diastolic blood pressure; use cautiously if taking herbs or supplements that lower blood pressure.

• Onion may inhibit bone resorption; use cautiously with herbs or supplements taken for osteoporosis.

• Onion may interfere with the way the body processes certain herbs or supplements using the liver's "cytochrome P450" enzyme system. As a result, the levels of other herbs or supplements may become too high or too low in the blood. It may also alter the effects that other herbs or supplements possibly have on the P450 system.

• Onion may also interact with antidepressants, antifungals, anti-inflammatory herbs and supplements, antioxidants, beta-carotene, fish oil, green tea, lecithin, p-glycoprotein-regulated herbs and supplements, hormonal herbs and supplements, selenium, soybean oil, and uridine diphosphate glucuronosyl transferase substrates.

Author Information

• This information is based on a systematic review of scientific literature edited and peer-reviewed by contributors to the Natural Standard Research Collaboration (www.naturalstandard.com).

References

Natural Standard developed the above evidence-based information based on a thorough systematic review of the available scientific articles. For comprehensive information about alternative and complementary therapies on the professional level, go to www.naturalstandard.com. Selected references are listed below.

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