This herb is a popular tea in South America. It contains caffeine (0.3-2.0%), and is a stimulant and a diuretic. The American Herbal Products Association notes that this herb is not recommended for excessive or long-term use. VirtualNutritionist.com notes:
"Excessive consumption of maté may lead to nervousness, and dehydration from its diuretic action. Large doses may cause nausea. Epidemiologists have noticed an association between maté drinking and an increased risk of cancer of the esophagus and kidney. Researchers are unsure, however, what part other factors, including the extremely hot temperature of the beverage that some maté drinkers prefer, tobacco use, and consumption of alcohol and red meat, may play in the increased cancer risk."