Some dieters say that guaraná helps improve weight loss results.

The herb guaraná contains caffeine and the closely related alkaloids theobromine and theophylline; these compounds may curb appetite and increase weight loss. Caffeine’s effects are well known and include central nervous system stimulation, increased metabolic rate, and a mild diuretic effect.¹ In a double-blind trial, 200 mg per day of caffeine was, however, no more effective than a placebo in promoting weight loss.² Because of concerns about potential adverse effects, many doctors do not advocate using caffeine or caffeine-like substances to reduce weight.

Guaraná contains substances similar to caffeine that could be responsible for caffeine-like responses in the body, including central nervous system stimulation, increased metabolic rate, and a mild diuretic effect.³ There is no research demonstrating guaraná is effective for weight loss on its own.

As with any caffeinated product, guaraná may cause insomnia, trembling, anxiety, palpitations, and urinary frequency.⁴ Guaraná should be avoided during pregnancy and breast-feeding.