Benefits
Faster reaction time after a single dose
A pooled analysis of eight placebo-controlled trials with 328 participants found that one dose of guarana gave a small gain in response speed with no change in accuracy; averaged across all cognitive measures the effect was less than trivial. Some single trials saw better attention or memory scores, while a later crossover trial found no cognitive effect.
Alertness and mental energy ratings
In placebo-controlled crossover studies, single doses of a guarana extract raised self-rated alertness and contentment, and caffeine-matched guarana powder raised alertness ratings more than placebo but not more than caffeine. In another crossover trial, 500 mg of guarana gave no consistent benefit on mood or mental workload.
Endurance and intermittent exercise output
In 11 endurance-trained adults, 500 mg of guarana before cycling raised work done in a 15-minute time trial by a small amount versus placebo, but not versus caffeine. In 27 youth soccer players, 3 g of seed powder raised distance in an intermittent running test but did not change jump height, sprint or agility. Both trials were small and single-dose.
Cognition over months of daily use in older adults
In a double-blind study, 45 healthy older volunteers took 1 g of guarana powder, caffeine or placebo every day for 5 months. Memory, psychomotor and reasoning scores did not differ between groups; one visual-spatial test improved with guarana, but that group started with higher scores. This is the only cited study of repeated use for mental performance.
Fatigue ratings in placebo-controlled clinical trials
In a crossover trial in 75 women receiving chemotherapy for breast cancer, guarana extract 50 mg twice a day for 21 days improved fatigue questionnaire scores versus placebo. A later pooled analysis of three breast cancer trials found no difference from placebo and rated the evidence very low quality. Guarana is not a treatment for cancer or its side effects.
Mechanism of action
Caffeine concentrated in the seed
Across five guarana cultivars, caffeine built up in the seed at 3.3 to 5.8 percent, while leaves, stems and fruit husk held mainly theobromine, and levels were highest in young tissue. Commercial materials vary: seed powders used in two trials tested at 2.1 and 3.99 percent caffeine, and an extract used in an attention study was about 12 percent.
Effects reported at low caffeine doses
A 75 mg extract containing about 9 mg of caffeine improved attention task speed, and in a multi-dose study the two lowest extract doses gave more positive cognitive effects than the higher ones. The authors argue caffeine alone may not explain this, but trials that matched caffeine doses could not separate guarana from caffeine.
Tannins and saponins: an untested slow-release idea
Guarana seed is rich in polyphenols: total tannins have been estimated at 5 to 14 percent, one tested seed powder held 16 percent, and the seed also contains saponins. These have been proposed as contributors to its effects, and it is often said they slow caffeine absorption, but none of the human trials cited here measured absorption rate or duration of effect.
Lower perceived effort during exercise
In a cycling trial, guarana did not change oxygen uptake, heart rate, fuel use, blood glucose or lactate, and perceived exertion at one time point was lower than with caffeine but not lower than with placebo. The authors suggest any exercise effect works through the brain rather than muscle metabolism, a proposal the trial did not test.
Clinical trials
Double-blind crossover trial of 500 mg guarana (130 mg caffeine), 100 mg caffeine or placebo, with Simon and 2-back tests before and 60 minutes after dosing and heart rate variability recorded (Talik et al. 2024, Nutrients)
20 participants; 11 also repeated the tests after physical fatigue.
Response times and heart rate variability did not differ between treatments, and neither guarana nor caffeine improved cognition after exercise. The authors conclude that neither influenced cognitive performance or gave a consistent benefit on mood or mental workload at these doses.
Systematic review and random-effects meta-analysis of placebo-controlled trials of a single dose of guarana on cognitive tasks (Hack et al. 2023, Nutrients)
8 studies with 328 participants; guarana doses of 37.5 to 500 mg supplying 4.3 to 100 mg caffeine.
Averaged across all cognitive measures the effect was less than trivial (g = 0.076, p = 0.14). Response time was faster with guarana (g = 0.202, p = 0.005) while accuracy did not change. The effect was not related to dose, and whether it comes from caffeine or other compounds is unknown.
Double-blind, counterbalanced, placebo-controlled study of single 37.5, 75, 150 and 300 mg doses of a standardized guarana extract (PC-102), testing cognition and mood through the day (Haskell et al. 2007, J Psychopharmacol)
26 participants.
Guarana improved secondary memory performance and raised alert and content mood ratings. The two lower doses produced more positive cognitive effects than the higher doses, and the authors suggest the effects cannot be attributed to caffeine alone.
Double-blind, counterbalanced, placebo-controlled study of single doses of 75 mg guarana extract (about 12 percent caffeine), 200 mg Panax ginseng and the combination, with tests up to 6 hours after dosing (Kennedy et al. 2004, Pharmacol Biochem Behav)
28 healthy young adults aged 18 to 24.
Guarana improved attention task speed, with some evidence of reduced accuracy, and improved sentence verification and serial subtraction tasks compared with placebo. The guarana dose held about 9 mg of caffeine, which the authors judged unlikely to explain the effects.
Double-blind randomized study of 1 g guarana powder a day (500 mg twice a day, 2.1 percent caffeine), caffeine capsules or placebo for 150 days, with memory, psychomotor, attention and reasoning tests at months 3 and 5 (Galduróz et al. 1996, Sao Paulo Med J)
45 healthy older volunteers aged 60 to 76 (mean 65), 15 per group.
The abstract reports no significant cognitive changes. In the full text, memory and reasoning scores did not differ between groups; the guarana group improved on one visual-spatial test (Mosaic), but it had started with higher scores. Three people taking guarana reported stomach burning, and one stopped because of a clinically confirmed fast heart rate.
Double-blind crossover trial of 100 mg caffeine, 500 mg guarana (130 mg caffeine) or placebo before 60 minutes of fixed cycling and a 15-minute time trial (Penna et al. 2024, Int J Sport Nutr Exerc Metab)
11 endurance-trained adults (cyclists and noncyclists).
Work in the time trial was higher with guarana than placebo (241.4 vs 232.1 kJ, effect size 0.18, p = .046), but guarana did not differ from caffeine and caffeine did not differ from placebo. Oxygen uptake, fuel use, glucose and lactate did not change, and strength loss after exercise was not reduced. The authors call the effect trivial to small.
Randomized, double-blind, counterbalanced crossover trial of a drink with 3 g guarana seed powder or placebo 60 minutes before field tests, with a 7-day washout (Estrázulas et al. 2024, J Am Nutr Assoc)
27 under-17 soccer players from a professional club.
Guarana increased distance covered in the Yo-Yo Intermittent Recovery Test level 1 compared with placebo (p = 0.01). It did not improve countermovement jump, 10 or 20 m sprints, or agility.
Randomized double-blind crossover trial of guarana powder (125 mg per kg, matched to the caffeine arm), caffeine (5 mg per kg) or placebo, with reaction time, word recall and mood tested before and after a maximal cycling test (Gurney et al. 2023, Br J Nutr)
25 participants.
Guarana shortened choice reaction time before exercise and simple reaction time after exercise compared with placebo, but not compared with caffeine. Alertness ratings were higher than with placebo. VO2max, immediate word recall and other mood scales did not change.
Randomized placebo-controlled crossover trial of guarana 50 mg by mouth twice a day for 21 days, a 7-day washout, then the opposite arm (de Oliveira Campos et al. 2011, J Altern Complement Med)
75 women with progressive fatigue after their first cycle of chemotherapy for breast cancer (32 started on guarana, 43 on placebo).
Guarana improved FACIT-F, FACT-ES and Brief Fatigue Inventory scores versus placebo on days 21 and 49 (p < 0.01); the Chalder scale improved on day 21 but not day 49. No grade 2 to 4 adverse events were recorded, and sleep, anxiety and depression scores did not worsen. This was a single short trial in a clinical population.
Systematic review of clinical studies using guarana as a dietary supplement for fatigue, with a meta-analysis of the trials sharing tumor and treatment types (de Araujo et al. 2021, Support Care Cancer)
7 studies with 427 cancer patients; 3 breast cancer trials pooled.
Guarana did not reduce fatigue compared with placebo (mean difference -0.02, 95% CI -1.54 to 1.50, p = 0.98), and the GRADE quality of evidence was very low.