Yerba Mate (tea) is made from the leaf of the plant Ilex paraguariensis. It contains caffeine, theophylline, theobromine, and related chemicals that are all stimulants.

Although Yerba Mate is widely used in South America, there unfortunately appears to be gathering evidence that chronic use of Mate increases the risk of several cancers, including bladder (De Stefani 1991), oral, esophageal (throat) (Pintos 1994), and lung (De Stefani 1996). There is also one case report of a woman who had liver problems after long-term use of Yerba Mate (McGee 1976). Because of the nature of correlative cancer studies, it is important to note that the exact cause of the cancer increases has not been identified and there is still the possibility that the Yerba Mate is not the direct cause of the increased cancer rates among users.

• As with other caffeine-containing teas, Yerba Mate's caffeine and theobromine will interact with a wide variety of pharmaceuticals and can increase heart rate and blood pressure.
  
  
• Caffeine is known to cause decreased blood levels of benzodiazepines such as diazepam (Valium) or alprazolam (Xanax).
  
  
• Caffeine is known to cause diueresis (increased urination).

• Adverse reactions to Yerba Mate are likely to be the same as with other caffeine-containing teas, coffees, or drinks. At lower doses, unwanted symptoms can include restlessness, reduced patience, irritability, difficulty falling asleep, and other mild-stimulant reactions.
  
  
• At higher doses, adverse reactions include nausea, vomiting, headaches, and unconsciousness. Very high doses of caffeine can be fatal, although it is nearly impossible to accidentally reach those levels using tea.

See the Caffeine Vault.