Supplements
garlic prevents the common cold
In plain terms: Does garlic prevent colds?
Part of: 🧪 Garlic
Possibly, but on very thin evidence: one small trial that was never repeated found fewer colds with garlic, while a second trial of a different garlic product found no fewer colds, only milder ones.
🧭 Read this score with how it was built in mindWe re-read the papers behind these claims and corrected how each one is counted
Off 'not enough evidence' by arithmetic, not by new evidence: the Cochrane review on this page contains exactly one trial, which was already counted, so it now sits as a review rather than a second vote. What remains is one small industry-linked trial reporting fewer colds against one trial reporting none. One versus one is a lean, not a finding.
📅 Last reviewed: 2026-07-15 ⓘ
Evidence ladder
How far up the ladder this claim has climbed. A high consensus on a low rung means "consistent so far," not "proven in people."
Top evidence so far: Human trials (RCT / n-of-1)
How the studies fall
What the evidence shows
Leans support on the arithmetic, but it is one small trial against one. Josling 2001 (n=146, 180 mg allicin for 12 weeks) reported 24 colds versus 65 on placebo — self-reported, industry-linked, never replicated — and Cochrane, finding it the only eligible trial, judged the evidence insufficient. The other RCT (aged garlic extract 2.
The evidence (5)
| Source | Grade | Stance | Quality | Finding |
|---|---|---|---|---|
| Percival SS 2016 · J Nutr | RCT | contradicts | low | J Nutr supplement paper by the trial's senior author summarising her own RCT: 'Healthy human participants (n = 120), between 21 and 50 y of age, were recruited for a randomized, double-blind, placebo-controlled parallel-intervention study to consume 2.56 g AGE/d or placebo supplements for 90 d' (NCT01390116). 'After 90 d, although the number of illnesses was not significantly different, the AGE group showed reduced cold and flu severity'. Duplicate population: this is the same trial already counted on this claim as garlic-nantz-2012 (NCT01390116, n = 120), so this row is subsumed and carries zero weight. On the prevention object the finding is a null -> contradicts; severity is off-object. |
| Josling P 2001 · Adv Ther | RCT | supports | moderate | RCT n=146: allicin garlic 24 vs 65 colds (p<.001), fewer sick-days - THE single trial the Cochrane rests on; self-reported, industry-linked, never replicated. |
| Lissiman E, Bhasale AL, Cohen M 2014 · Cochrane Database Syst Rev | meta-analysis | tested-null | moderate | Cochrane review: 'only one trial met the inclusion criteria' - 146 participants, garlic supplement with 180 mg allicin vs placebo for 12 weeks: '24 occurrences of the common cold in the garlic intervention group compared with 65 in the placebo group (P value < 0.001)'. That sole trial is Josling 2001, already counted as garlic-josling-2001; the review pools nothing new. Conclusion: 'insufficient clinical trial evidence'. Duplicate population of Josling 2001 - zero weight; the primary keeps the vote. |
| Nantz MP, Rowe CA, Muller CE, Creasy RA, Stanilka JM, Percival SS 2012 · Clin Nutr | RCT | contradicts | low | Double-blind placebo-controlled parallel RCT, 120 healthy adults (60/group), aged garlic extract 2.56 g/d x90 d: 'the incidence of colds and flu, a secondary outcome, were not statistically different' (no estimate/CI in abstract). That null on incidence is the claim's object (prevention) -> contradicts. The severity reductions (21% fewer symptoms, 61% fewer sub-optimal days, 58% fewer missed work/school days, z-tests of proportions) are off-object for a prevention claim and go to candidates, not mixed. Primary aim was gd-T/NK cell proliferation; incidence is self-reported diary 'colds and flu' combined, not colds alone. |
| Li L, Sun T, Tian J, Yang K, Yi K, Zhang P 2013 · Crit Rev Food Sci Nutr | meta-analysis | tested-null | moderate | Overview of systematic reviews, no own pooling: 'We described nine SRs about garlic.' On the cold: 'Garlic as a preventative or treatment option for the common cold ... could not be recommended, as only one relatively small trial evaluated the effects separately.' Re-describes a trial already held via its parent review - zero weight. |
Disagree, or know a study we missed?
We grade by evidence, not opinions. The way to weigh in is to point us to a study we haven't cited (check the evidence table above first), or to flag a problem with one we have. Every submission is reviewed; if it holds up, the grade updates and shows in Science Changes Its Mind.
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Educational only, not medical advice. Grades and scores reflect published evidence weighted by study design and quality; see the methodology.