A friend suggested that I try yerba mate tea to boost my energy. What is yerba mate? Is it safe? Yerba mate isn't likely to pose a risk for healthy adults who occasionally drink it. However, some studies indicate that people who drink large amounts of yerba mate over prolonged periods may be at increased risk of some types of cancer, such as cancer of the mouth, esophagus and lungs. Smoking in combination with yerba mate seems to greatly increase the cancer risk.