According to 17 selected studies, there's a significant chance that zinc lozenges reduce cold durations by 17%.

👇 See how changing the included studies changes this result.

What is this?

I explain it more fully in my blog post, but this page is an experiment to see how we can improve medical information on the internet.

I believe that good medical communication is quantitative, exhaustive, and accessible—this page strives as much as possible to be all three!

💡 Tips
  • It's interactive! Choose which trials you'd like to include in your analysis (based on trial design, dosage, zinc formulation, etc.).
  • Compare with published reviews. Click the column headers to se which trials were included in peer-reviewed meta-analyses. It's interesting to see why they got different results!
  • The URL is shareable. Once you've selected the trials you like, you can share the URL and others will be able to see your selections.
  • I want feedback! Hate it? Really want to give me a piece of your mind? Reach out via email ( or Twitter (@tomjcleveland).

Forest plot

Welcome to the forest plot! Each row represents a (randomized, controlled) clinical trial, and the 𝚫 column tells you the percent change in cold duration between the zinc group and the placebo group for that trial (negative numbers mean the zinc group had shorter colds).

The middle columns show which trials were included in the existing systematic reviews on zinc lozenges. Try clicking on the headers to see their results!

Last updated ???

Trial 𝚫 95% CI Plot

Search strategy and included trials

Every week I search the Cochrane Central Register of Controlled Trials (CENTRAL), which aggregates results from other popular databases like PubMed, Embase, and

I then exclude the results that aren't relevant (see adjacent panel). My screening criteria are intentionally lax—the point of this page is to provide an exhaustive list of relevant data, and let visitors decide which trials are worth looking at.

Search terms  
zinc AND cold
110 Trials
Inclusion criteria
    Randomized, controlled trial
    Humans with common cold
    Zinc lozenges (alone)
    Placebo lozenges
    Duration of cold symptoms
Total included
17 trials

Funnel plot

Funnel plots are used to gauge whether the results of candidate reviews are distributed like we'd expect.

For a given set of trials, we'd expect large trials to have outcomes that cluster close to the true effect size (the top of the funnel), while smaller trials would have outcomes that are more widely distributed (the bottom of the funnel).

In theory, 95% of trial results should lie inside the funnel. In addition, these results should be distributed symmetrically on either side of the pooled effect size (center line).

Think we're missing a relevant trial or an published review?

Let us know