Methodology
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:
- Cochrane systematic reviews
- Other systematic reviews and meta-analyses of RCTs
- 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:
- USP Verified (usp.org) — Tests product identity, potency, purity, and dissolution
- NSF Certified for Sport (nsf.org) — Tests for 280+ banned substances plus label accuracy
- ConsumerLab (consumerlab.com) — Independent lab testing for label claims and contamination
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. Prices are updated regularly and each page notes its last data refresh date.
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
- We do not accept payment for product placement or rankings
- Rankings are determined by cost per effective dose, with quality-verified products highlighted separately
- All clinical claims cite their PubMed source directly
- All product data cites its NIH DSLD record where available
- We distinguish between evidence levels: systematic review > meta-analysis > individual RCT > observational
- Pages include affiliate links to the products discussed. This does not influence rankings or recommendations, which are determined by the data.
Limitations
- DSLD label data reflects manufacturer-submitted information. We do not independently test products.
- Pricing changes frequently. While we update regularly, prices may differ from what you see at checkout.
- Clinical evidence for supplement efficacy is generally weaker than for pharmaceutical drugs. We report what the evidence shows, including when results are mixed or inconclusive.
- This site provides information, not medical advice. Consult a healthcare provider before starting any supplement.