Which weight‑loss supplements have peer‑reviewed clinical trials supporting their effectiveness?
Executive summary
Randomized, peer‑reviewed clinical trials and meta‑analyses show that a handful of non‑prescription supplements produce small—but sometimes statistically significant—average weight losses versus placebo, notably spirulina, psyllium, chitosan, green tea extract, glucomannan/konjac, curcumin and a few others; however, effect sizes are modest, study quality and duration are heterogeneous, and leading systematic reviews conclude there is no overwhelmingly convincing evidence that any supplement produces meaningful, sustained weight loss for most people [1] [2] [3] [4].
1. Supplements with the strongest trial‑level signals of benefit
A 111‑trial network meta‑analysis found “high certainty” evidence that spirulina supplementation led to modest weight loss (mean difference −1.77 kg) and moderate‑certainty evidence that curcumin, psyllium, chitosan, Nigella sativa and green tea produced small reductions in body weight compared with controls, with reported mean differences generally around 0.8–3.7 kg depending on the agent [1].
2. Common supplements with mixed or marginal clinical trial results
Multiple authoritative reviews report mixed or low‑quality evidence for agents commonly marketed for weight loss: chromium picolinate has shown tiny average differences (~1.1 kg) of “debatable clinical relevance” and low overall evidence quality [5]; glucomannan/konjac trials report small effects in some meta‑analyses but overall uncertainty and frequent gastrointestinal adverse events in trials [6] [7]; and green tea extract appears in meta‑analyses to produce modest reductions in body mass and fat but findings vary by dose, population and study quality [8] [9].
3. Ingredients that appear in trials but raise safety or clinical‑relevance flags
Ephedra (and ephedrine‑containing supplements) showed weight‑loss signals in older trials but are linked to increased risk of adverse cardiovascular events and were singled out as unsafe in systematic reviews [2]; Garcinia cambogia/hydroxycitric acid has been tested in multiple randomized trials but systematic reviews conclude efficacy remains unproven and have flagged neuropsychiatric and gastrointestinal adverse events in some products [5] [7].
4. Notable positive findings that depend on combinations or context
Some trial evidence is conditional: for example, L‑carnitine produced additional weight loss only when combined with the pharmaceutical orlistat in one one‑year trial of people with uncontrolled type 2 diabetes, whereas L‑carnitine alone did not show benefit in another trial [5]. This highlights that some positive signals come from combination therapies or specific clinical subgroups rather than stand‑alone, over‑the‑counter use [5].
5. What major systematic reviews and clinical groups conclude
Large, recent systematic reviews and expert summaries — including a comprehensive RCT review that examined hundreds of trials and an Office of Dietary Supplements fact sheet — converge on the same headline: many supplements have been tested, a minority of trials show statistically significant but small differences, trials suffer from short duration, small sample sizes and heterogeneity, and overall evidence does not support strong, generalizable claims that non‑prescription supplements produce clinically meaningful, sustained weight loss [3] [4] [10].
6. Practical interpretation and caveats for clinicians and consumers
The evidence supports that certain nutraceuticals can produce small, short‑term reductions in body weight in randomized trials (examples: spirulina, psyllium, chitosan, green tea, curcumin, glucomannan), but effect sizes are modest, benefits rarely approach those seen with approved pharmacotherapies or lifestyle interventions, and safety, product quality, dose and trial context vary widely; consumers and clinicians should weigh the limited magnitude of benefit against uncertain long‑term effects and documented harms for some ingredients [1] [3] [2].