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.
These uses have been tested in humans or animals. Safety and effectiveness have not always been proven. Some of these conditions are potentially serious, and should be evaluated by a qualified healthcare provider.
Early study suggests that application of an alcoholic onion extract on the skin may reduce allergic responses, such as wheals ("hives") and flares. More research is needed in this area.
Study using topical onion juice increased hair regrowth in alopecia areata (hair loss) patients, especially women. More research is needed in this area to confirm these results.
Early evidence suggests that onion or onion extract prevents cancer, including gastrointestinal, ovarian, skin, and endometrial cancers. Some studies, however, have reported no association between Allium vegetable consumption and incidence of cancer (particularly breast and lung cancer). More research is needed before a conclusion can be made.
One clinical trial found that fresh onion significantly decreased serum glucose (blood sugar) levels in diabetics. More research is needed in this area to confirm these results.
Early evidence suggests that consumption of onions and other vegetables belonging to the Allium genus may reduce the risk of heart attack. More well designed studies are needed before a conclusion can be made.
Onion-olive oil capsules may help lower blood pressure, although additional research is needed to make a firm conclusion.
Research in humans found that onion may have an effect on blood serum triglyceride, betalipoprotein cholesterol and phospholipid levels. More research is needed in this area to confirm these results.
Several trials have been conducted using combination products that include an onion extract. These studies have investigated onion's potential role in scar healing in adults and children, specifically due to injuries from laser tattoo removal or surgery. The overall results are mixed, and more research is needed to make a conclusion.
* Key to grades
A: Strong scientific evidence for this use B: Good scientific evidence for this use C: Unclear scientific evidence for this use D: Fair scientific evidence for this use (it may not work) F: Strong scientific evidence against this use (it likley does not work)
Tradition / Theory
The below uses are based on tradition, scientific theories, or limited research. 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 healthcare provider. There may be other proposed uses that are not listed below.
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.
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.
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.
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.
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The information in this monograph is intended for informational purposes only, and is meant to help users better understand health concerns. Information is based on review of scientific research data, historical practice patterns, and clinical experience. This information should not be interpreted as specific medical advice. Users should consult with a qualified healthcare provider for specific questions regarding therapies, diagnosis and/or health conditions, prior to making therapeutic decisions.