The Yerba Mate Debate: Caffeine vs. Mateine

Yerba mate fanatics claim that it is caffeine-free and instead, contains a substance called "mateine," a stereoisomer of caffeine. However, experts state that caffeine has no stereoisomers and researchers at the Florida International University in Miami – as reported by Wikipedia - have found that mate does contain caffeine, but some people seem to tolerate it better than coffee or tea.
Mate drinkers report experiencing physiological effects such as mental wakefulness, alertness and focus but minus the negative effects like jitteriness, palpitations, anxiety or diarrhea, which sometimes accompanies taking stimulants such as coffee.

EcoTeas, an online seller of Yerba mate, suggests that the main distinction between caffeine and mateine is that caffeine is a "substance" while mateine is an "effect." They further add that "maybe the issue is not with the chemical structure of the stimulant in yerba mate, but with a culture that insists on isolating a single active ingredient in this dynamic, holistic, natural herb. When you combine the nutrition, antioxidants, caffeine, theophylline, and theobromine that all naturally occur in yerba mate, you get a whole that is greater than the sum of its parts."