In the United States, guarana has received the designation of "generally recognized as safe" by the American Food and Drug Administration.
Preliminary research has shown guarana may affect how quickly the body perceives itself to be full. One study showed an average 11.2-pound (5.1-kilogram) weight loss in a group taking a mixture of yerba mate, guarana, and damiana, compared to an average one pound loss in a placebo group after 45 days. Although inconclusive about specific effects due only to guarana, this study differs from another showing no effect on body weight of a formula containing guarana.
Guarana extract reduced aggregation of rabbit platelets by up to 37 percent below control values and decreased platelet thromboxane formation from arachidonic acid by 78 percent below control values.