Supplements

garlic prevents the common cold

In plain terms: Does garlic prevent colds?

Insufficient Supplements 💰 Industry COI noted🔬 Includes disconfirming🔎 Limited evidence — fewer than 12 studies

RefutedContestedStrong support

consensus score 0.19

⚖️ Thin evidence — read the needle loosely. The score shows which way the studies lean, but there are too few independent, high-quality ones to place it firmly. Expect this to move as better evidence arrives.

There isn't enough good evidence to say. The idea rests on essentially one small study; the Cochrane review that examined it rated the evidence insufficient and poor-quality, and a second trial found no drop in how often people caught colds. Possible, but unproven.

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)

MechanismIn-vitroAnimalObservationalRCTMeta-analysis

How the studies fall

1 support 0 contradict 2 tested null 2 mixed · 5 sources, 1 independent group

What the evidence shows

The evidence that garlic prevents colds is **thin**. The Cochrane review found only ONE adequate trial in decades of searching — it hinted at fewer self-reported colds but was rated poor-quality/insufficient. The one other RCT found no drop in cold *incidence* (only secondary symptom measures), and was industry-funded. Not enough good evidence to say.

The evidence (5)

Source	Grade	Stance	Quality	Finding
Percival SS 2016 · J Nutr	RCT	mixed	low	RCT n=120: aged garlic - cold INCIDENCE not reduced (primary null); severity/sick-days reduced + NK/gd-T cell activation (same UF cohort as Nantz).
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 et al. 2014 · Cochrane Database Syst Rev	meta-analysis	tested-null	moderate	Cochrane review: only 1 trial (n=146) qualified across decades; it showed fewer self-reported colds but the review concluded evidence is INSUFFICIENT / poor quality.
Nantz MP et al. 2012 · Clin Nutr	RCT	mixed	low	RCT (n=120) aged garlic extract: cold INCIDENCE not reduced (primary null); symptom severity / sick-days reduced (secondary). Industry-funded, single lab.
Li XL et al. 2013 · Crit Rev Food Sci Nutr	meta-analysis	tested-null	moderate	Umbrella review of 9 systematic reviews: garlic for the common cold 'could not be recommended' - only one small trial exists.

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.