Awaiting clinical review. This entry is sourced but has not yet been signed off by a pharmacist or clinician.

Paullinia cupana (seed)

Guarana

Guarana is a caffeine-rich seed, and whatever alertness it gives you is most likely the caffeine. A 2023 meta-analysis found only a small speed-up in response time and no change in accuracy, and guarana did not beat placebo for cancer-related fatigue. The main caution is hidden caffeine: labels can be vague, so add it to your daily total (EFSA's no-concern level for healthy adults is 400 mg a day from all sources).

Written by

Healthy and Herbal editorial team

Updated

29 September 2026

At a glance

Last reviewed 29 September 2026

Evidence

Limited

Best for

Alertness and reaction time

Typical form & use

Seed extract, 37.5–500 mg

Onset

Same night

Safety

Contains caffeine; count it in your daily total. No interactions in our data.

Check with your medications →

What it's used for

Evidence is rated per use. The same ingredient can be strong for one thing and traditional for another.

Use	Evidence	What the research shows
Cognitive performance (reaction speed)	Limited	A meta-analysis of eight placebo-controlled trials (328 people, single doses of 37.5–500 mg guarana) found a trivial overall effect (Hedges' g 0.076, p = 0.14). Response times were slightly faster (g 0.202, p = 0.005) while accuracy was unchanged (g −0.077, p = 0.4). Effect did not track the dose, and it is unknown whether the caffeine or something else in guarana was responsible.¹
Everyday tiredness and alertness	Limited	We found no trial reviewed here of guarana in otherwise healthy tired adults. A pharmacy review concludes there is no evidence for guarana's effects beyond those attributable to its caffeine, and EFSA says caffeine increases alertness and reduces sleepiness, with effects starting 15 to 30 minutes after a dose. We therefore rate this on the caffeine evidence, not on guarana-specific trials.^4,7
Cancer-related fatigue	Limited	A 2021 systematic review of seven studies (427 patients) pooled three breast cancer trials and found no difference from placebo (mean difference −0.02, 95% CI −1.54 to 1.50), with very low quality evidence. An earlier crossover trial of 50 mg twice daily in breast cancer chemotherapy patients reported better fatigue scores, but two later trials of a purified extract (PC-18) were not better than placebo.^2,3,5

How much

Ranges below are what studies used and what supplements commonly contain. They are not a recommendation for you. Start at the low end.

Studied range

37.5–500 mg guarana¹

Single doses in the cognitive trials. The caffeine those doses supplied was reported as 4.3–100 mg, so guarana strength varies between products.

Fatigue trials

50 mg twice daily^3,5

Dry extract for 21 days in the one trial that found a benefit for chemotherapy-related fatigue. Later trials of a purified extract at 7.5–37.5 mg twice daily found no advantage over placebo.

Caffeine ceiling (adults)

400 mg/day, 200 mg at once⁷

EFSA's levels that raise no safety concern for healthy adults from all sources, including guarana. Not a guarana-specific limit.

Caffeine ceiling (pregnancy)

200 mg/day⁷

EFSA's no-concern level for pregnant and lactating women, from all sources.

Timing · EFSA notes single doses of caffeine as low as 100 mg may affect sleep in some adults, particularly close to bedtime, so keep guarana to the daytime.With food? · No source we read gave food guidance for guarana.How long to trial · Caffeine effects begin within 15 to 30 minutes (EFSA), so you can judge it in a day. The cancer fatigue trials used 21 days.

How people take it

Powder, tablet or capsule (seed)Follow the label; check caffeine per servingGuarana seeds are ground to a powder and sold as powder, tablets and capsules. Caffeine content differs between products.

Dry extract (capsule)37.5–500 mg in trialsThe form used in the clinical studies.

Energy drinks and mixed supplementsVariesGuarana is widely added to these products, and caffeine labelling on some is misleading. In one US analysis of 53 caffeine-containing supplements (including guarana products), daily caffeine ranged from 1 to 829 mg.

Safety

Who should avoid

Pregnancy and breastfeeding — keep total caffeine under 200 mg a day (EFSA)
Close to bedtime — 100 mg caffeine can disturb sleep in some adults
If you already have coffee, tea, cola or energy drinks — add up the caffeine
Children and adolescents — EFSA's caffeine limit is 3 mg per kg of body weight
Heart rhythm problems, anxiety or high blood pressure — ask your clinician first

Known interactions

No interactions in our data. Absence of a flag is not clearance.

Questions people ask

Is guarana stronger than coffee?

Guarana's main active constituent is caffeine, and a pharmacy review notes it has a high caffeine content. But the amount per serving depends on the product, so the label, not the plant name, is what matters.

Does guarana improve focus?

Slightly at best. A meta-analysis of eight trials found faster response times but no change in accuracy, and the overall effect was trivial. It is unclear whether guarana does anything that the same amount of caffeine would not.

How much guarana is safe?

There is no guarana-specific limit in the sources we read. A 2019 safety review found no serious risks when caffeine guidelines are respected. EFSA's caffeine levels are up to 400 mg a day for healthy adults (200 mg at once) and 200 mg a day in pregnancy, counting every source.

Does guarana help with cancer fatigue?

Not reliably. The 2021 systematic review found no benefit over placebo, and the evidence was rated very low quality. Speak to your oncology team before taking any supplement during treatment.

Sources

Last reviewed 29 September 2026 · Next review March 2027 · How we rate evidence