Verified Supplement Data Evidence-based supplement comparisons
Independent · no paid placement Every claim links to its primary source How we verify

Methodology

Last updated: March 15, 2026

Data Collection

Layer 1: Clinical Evidence

We search PubMed for systematic reviews and meta-analyses of randomized controlled trials (RCTs) for each supplement-condition pair. We prioritize the highest level of evidence:

  1. Cochrane systematic reviews
  2. Other systematic reviews and meta-analyses of RCTs
  3. Individual RCTs (when no systematic review exists)

From each review, we extract: ingredient form studied, dosage range, study population, sample size, primary outcome, effect size (when reported), and author conclusions. Every claim links to its PubMed ID for verification.

Layer 2: Product Label Data

Product ingredient data is sourced from the NIH Dietary Supplement Label Database (DSLD), a public database maintained by the National Institutes of Health Office of Dietary Supplements. The DSLD contains over 207,000 supplement labels with verified ingredient names, forms, quantities per serving, serving sizes, and daily value percentages.

We cross-reference DSLD data against manufacturer websites to confirm currently available products and serving information.

Layer 3: Quality Verification

We check each product against the three major third-party certification databases:

Certification status is verified at the time of publication and noted with the verification date. The absence of certification does not indicate a product is unsafe — only that it has not been independently tested by that organization.

Layer 4: Pricing

Prices are collected from Amazon retail listings and brand direct-to-consumer websites. We report the standard retail price (not Subscribe & Save or promotional pricing) to ensure comparability. Because retail prices change frequently, the live retailer price is always the source of truth — if a figure here is stale, the price you see at checkout governs.

Data Freshness & Provenance

Our full product catalog — prices, certifications, and DSLD label data — was last reviewed end-to-end in March 2026. We re-verify on a periodic basis rather than claiming a daily refresh we don't perform; we'd rather tell you the real review date than print today's date on data we haven't re-checked. Clinical evidence and PubMed citations are reviewed when the underlying literature changes.

If you find an outdated price, a changed certification, or a claim that no longer holds, tell us. Every fix we make is logged publicly on our corrections page.

Cost Per Effective Dose Calculation

This is our core normalization metric. Rather than comparing cost per serving (which varies based on arbitrary serving sizes), we calculate what it costs per day to take the clinically-studied dose.

Formula:

Cost per day = (product price ÷ servings per container) × (clinical daily dose ÷ amount per serving)

The clinical daily dose is determined from Layer 1 evidence — specifically, the dosage used in the most robust positive clinical trials for the stated condition. When trials use a range of doses, we use the most commonly effective dose.

Editorial Standards

Limitations