Animal studies suggest guarana, either as a single dose or taken long term, improves memory function. Small human studies using healthy elderly volunteers have not borne this out, although a recent small study using young volunteers did report positive effects on concentration. A study of 129 healthy people found that a multivitamin and mineral supplement with guarana improved speed and accuracy and delayed fatigue. Creatine has also been used to improve exercise capacity, including endurance, in people with congestive heart failure.
