Which clinical trials tested guarana alone (not in stimulant mixtures) for weight loss, and what doses were used?
Executive summary
Clinical trials that tested guarana (Paullinia cupana) by itself for weight loss in humans are scarce; most human trials cited in the literature evaluate guarana as part of multi-ingredient stimulant blends, and the few studies of guarana alone have used low doses and measured metabolic biomarkers rather than clear weight-loss outcomes [1] [2] [3]. Animal experiments used much higher, clearly quantifiable doses (grams per kilogram), but those cannot be directly translated into proven, effective human weight‑loss regimens [4] [5].
1. Only a handful of human trials used guarana alone — and they didn’t prove weight loss
Systematic and narrative reviews state explicitly that very few clinical trials have administered guarana by itself and that no human study has definitively demonstrated efficacy or safety of guarana as a lone weight‑loss agent [2] [3]. Clinical overviews and consumer‑health sources reiterate that most positive weight‑loss signals reported in humans come from products that combine guarana with other stimulants (notably ephedra/ephedrine) or with green tea extracts, making it impossible to isolate guarana’s contribution to weight change in those trials [1] [6] [7].
2. The clearest human trial of guarana alone used 90 mg/day but assessed biomarkers, not sustained weight loss
A small randomized, controlled single‑blind trial tested “minimal” guarana supplementation at about 90 mg/day of guarana powder for 14 days and evaluated lipid, glucose and other metabolic biomarkers in 14 overweight volunteers; that study did not present robust data showing clinically meaningful weight loss over that short period [8]. This trial illustrates two recurring problems in the literature: trials with guarana alone are small and short, and they focus on intermediate metabolic endpoints rather than durable weight reduction [8] [3].
3. Major human weight‑loss evidence stems from mixtures that include guarana plus other stimulants
The most-cited randomized trial often discussed in weight‑loss debates tested a commercial herbal supplement combining Ma Huang (ephedra; ~72 mg/day ephedrine alkaloids) with guarana delivering about 240 mg/day caffeine total in the product and reported short‑term weight and fat loss — but this was a combination product, so the weight effect cannot be attributed to guarana alone [1] [6]. Reviews and clinical summaries repeatedly flag that ephedrine‑plus‑caffeine synergy explains much of the observed thermogenesis and weight loss in such mixtures, and also raises safety concerns for long‑term use [1] [2].
4. Animal studies used much higher guarana doses, showing metabolic effects but not human proof
Preclinical experiments give clear dosing numbers: mice fed guarana at 1 g/kg body weight showed increased mitochondrial biogenesis and attenuation of diet‑induced weight gain, and rat studies tested whole extract doses around 0.130–0.325 g/kg [4] [5]. These studies demonstrate plausible mechanisms—thermogenesis, brown‑fat activation, lipid‑metabolism changes—but authors and reviews cautioned that translation to humans requires controlled clinical trials at safe, well‑defined doses [4] [9].
5. Why the literature leaves the question unanswered: gaps and practical implications
Authoritative summaries—drug monographs and clinical reviews—underscore the evidence gap: limited guarana‑alone trials, small sample sizes, short durations, and frequent confounding by added stimulants prevent any confident clinical recommendation for guarana alone for weight loss [2] [10] [11]. Where human data exist, doses range from brief low‑dose supplements such as 90 mg/day (biomarker trial) to products supplying hundreds of milligrams of caffeine in combination formulas [8] [6], but none establish guarana‑alone efficacy for sustained weight reduction [3].
6. Bottom line — what the clinical record actually shows
There is no robust, replicated clinical trial that tests guarana by itself and demonstrates meaningful weight loss in humans; the few human studies of guarana alone used low doses (for example ~90 mg/day for 14 days) and measured biochemical effects rather than durable weight change, while the stronger human weight‑loss signals all come from multi‑ingredient stimulant combinations where guarana’s independent role cannot be separated [8] [1] [6] [3]. Animal studies report effective doses in the gram‑per‑kilogram range, but these are mechanistic and not substitutes for human clinical proof [4] [5].