Yerba mate is used to making a beverage known as a mate. When served cold, the drink is called tereré in Guaraní. It is traditionally consumed in central and southern regions of South America, primarily in Paraguay, as well as in Argentina, Uruguay, southern and central-western Brazil, the Chaco region of Bolivia and southern Chile
Yerba mate is popular in Paraguay, where people are seen walking the streets carrying the mate and termo (thermal vacuum flask) in their arms.
The flavour of brewed mate resembles an infusion of vegetables, herbs, grass and is reminiscent of some varieties of green tea. Some consider the flavour to be very agreeable, but it is generally bitter if steeped in boiling water. Flavoured mate is also sold, in which the mate leaves are blended with other herbs (such as peppermint) or citrus rind.
In Paraguay a mate infusion, called tereré in Spanish is consumed as a cold or iced beverage, usually sucked out of a horn cup called guampa with a bombilla. Tereré can be prepared with cold water (the most common way in Paraguay).
Paraguayans have a tradition of mixing mate with crushed leaves, stems, and flowers of the plant known as flor de Agosto (the flower of August, plants of the genus Senecio, particularly Senecio grisebachii), which contain pyrrolizidine alkaloids. Modifying mate in this fashion is potentially toxic, as these alkaloids can cause a rare condition of the liver, veno-occlusive disease, which produces liver failure due to progressive occlusion of the small venous channels in the liver.