Yerba mate provides 25 mg of caffeine per 2g tea bag in 8 oz of water. For comparison, the average cup of coffee has 135 mg of caffeine. The average cup of black tea contains 50 mg. Green tea has 30 mg.
Not all 'caffeines' are the same, however. What we refer to as 'caffeine' is really a group of substances known to chemists as Xanthine Alkaloids. The caffeine in coffee is very physical and quick to take effect. Theophylline is the 'caffeine' found in green tea. It tends to be very mental. Theobromine is the 'caffeine' found in chocolate. It tends to be very slow-releasing.
Yerba mate actually contains a mixture of these three xanthine alkaloids. It also provides minerals to support nervous system function, and B-vitamins to relax muscles. For these reasons, it produces a balanced, long-lasting physical and mental stimulation.
At one point, South American chemists were so intrigued by the qualitative difference between yerba mate stimulation and coffee stimulation that they invented a phantom molecule called mateine to explain it. They claimed that mateine was a unique molecule in the xanthine alkaloid family. We now know this is not the case, though we still sometimes refer to mateine as the holistic effect of drinking yerba mate.
Yerba mate receives a lot of press as a diet and weight-loss tea. While nothing can replace a healthy diet, regular exercise, and a great attitude, yerba mate can certainly give you a boost: