Onion is not only a food that adds flavor, but it is also a medicinal herb. Medicines such as quercetin and Mederma have onion as one of their main constituents. Onion also provides alk(en)yl cysteine sulfoxides including S-methyl cysteine sulfoxide and S-propyl cysteine sulfoxide, cycloalliin, thiosulfinates, and sulfides, which are ingredients in many pharmaceutical medicines.

The onion protects from oxidative stress, protects against cancer, supports immunity, improves heart health, reduces inflammation, prevents and dissolves blood clots, improves bone health, prevents tumors, supports gut health, lowers blood pressure, helps with consitpation, regulates blood sugar, and, with garlic, it fights infectious disease. Studies have shown reduction of body fat from using onion extract. It is also a broad-spectrum antimicrobial.