Onion is a plant. The bulb (rounded underground part) of the onion is used to make medicine. Onion is used for treating digestion problems including loss of appetite, upset stomach, and gallbladder disorders; for treating heart and blood vessel problems including chest pain (angina) and high blood pressure; and for preventing “hardening of the arteries” (atherosclerosis). It is also used for treating sore mouth and throat, whooping cough, bronchitis, asthma, dehydration, intestinal gas, parasitic worms, and diabetes. Some people use it as a diuretic to increase urine output.
Onion is applied directly to the skin for insect bites, wounds, light burns, boils, warts, and bruises.
Scarring
Most research suggests that applying onion extract, usually as a specific product containing heparin and allantoin (Contractubex), to the skin for 10 weeks to 6 months improves scar colour and appearance, as well as pain and itching, in people with scars due to burns, tattoo removal, injuries, or surgical removement of tissue. However, using a specific product containing onion exract and allantoin (Mederma, Merz Pharmaceuticals) for 4-11 weeks does not seem to improve the appearance of new surgical scars.
Hair loss (alopecia areata)
Early research suggests that applying onion juice to the scalp for 8 weeks might improve hair growth in people with hair loss due to a condition called alopecia areata.
Diabetes
Early research suggests that adding onion three times daily to a specific diet for 8 weeks might reduce blood sugar in people with diabetes.
High blood pressure
Early research suggests that taking a specific product containing onion, olive oil, grape skin extract, L-carnitine, vitamin E, vitamin C, lycopene, and folic acid daily for one week might lower systolic blood pressure (the top number) but not diastolic blood pressure (the bottom number) in people with high blood pressure.
How does Onion work?
Onion might help reduce cholesterol levels, a risk factor for hardening of the arteries. There is some evidence that onion might also reduce lung tightness in people with asthma.
Are there safety concerns?
Onion is safe when taken by mouth in amounts commonly found in food or when applied to the skin. It is safe for most people when taken by mouth in larger amounts. Taking up to a maximum of 35 mg of the onion ingredient “diphenylamine” per day for several months seems to be safe.
Precautions
Pregnancy and breast-feeding: There is not enough reliable information about the safety of taking onion as a medicine if you are pregnant or breast-feeding. Stay on the safe side and avoid using onion in amounts larger than usual food amounts.
Bleeding disorder: Onion might slow blood clotting. There is concern that onion might increase the risk of bleeding when taken as a medicine. Don’t use medicinal amounts of onion or onion extract if you have a bleeding disorder.
Diabetes: Onion might lower blood sugar. If you have diabetes and use onion in medicinal amounts, check your blood sugar carefully.
Surgery: Onion might slow blood clotting and lower blood sugar. In theory, onion might increase the risk for bleeding or interfere with blood sugar control during and after surgical procedures. Stop using onion as a medicine at least 2 weeks before a scheduled surgery.
