Eucalyptus tea is very popular for curing a range of medical conditions. Eucalyptus leaves contain flavonoids (plant-based antioxidants), volatile oils and tannins. Eucalyptus leaves contain substances that have expectorant, antibacterial and antiseptic properties. One of these substances is a powerful chemical called eucalyptol, also known as cineole. This compound has the ability to loosen phlegm, ease coughs and fight many common upper respiratory problems.