Our scoring methodology
Every supplement reviewed on Health Britannica is scored using the same 6 proposition value metrics. This page explains exactly how we arrive at each score, so you can evaluate our recommendations with full transparency.
The 6 metrics
Evidence (0-10)
We evaluate the quality and quantity of clinical research supporting the supplement's claimed benefits. Scoring hierarchy: Systematic reviews/meta-analyses (highest) > randomized controlled trials > observational studies > animal studies > mechanistic/in-vitro > anecdotal. A score of 9+ means multiple human RCTs with consistent results. Below 6 means mostly animal/mechanistic evidence.
Purity (0-10)
Does the bottle match the label? We check for third-party certifications (NSF, Informed Sport, USP, ConsumerLab), heavy metal testing, label accuracy reports, and manufacturing standards (cGMP compliance). A 9+ means independently verified with published COAs.
Value (0-10)
Cost per clinically effective dose compared to alternatives in the same category. We calculate cost-per-serving at the researched dose (not the label dose if they differ). Premium brands can still score high on value if no cheaper equivalent exists at the same quality.
Efficacy (0-10)
Does the product deliver the researched dose in a bioavailable form? Many products contain the right ingredient at the wrong dose, or in a poorly absorbed form. We compare label doses to clinically studied doses and evaluate the delivery form.
Safety (0-10)
Side effect profile, drug interaction potential, and long-term safety data. We take a conservative approach: if long-term data is lacking, the score reflects that uncertainty. Known interactions with common medications are noted.
Synergy (0-10)
How well the supplement integrates with other products in its stack(s). Does it enhance absorption of cofactors? Does it have timing conflicts? Does it fill a unique role or overlap with something cheaper?
Score thresholds
| Score range | Classification | What it means |
|---|---|---|
| 8.0-10.0 | High confidence | Strong recommendation. Well-researched, well-made, good value. |
| 6.0-7.9 | Moderate confidence | Decent option with caveats. May lack evidence or value. |
| Below 6.0 | Low confidence | Not recommended. Better alternatives exist. |
Editorial independence
Our scores are never influenced by affiliate relationships. We frequently recommend budget options (NOW Foods, Nutricost) that pay lower commissions because they're genuinely the best value. No brand can pay for a higher score or preferential placement.
Affiliate disclosure
Health Britannica earns revenue through affiliate commissions. When you purchase a product through one of our links, we may earn a commission at no extra cost to you. Affiliate relationships are disclosed clearly on every article that contains affiliate links. Commission rates have zero influence on product scores or rankings. We maintain a strict separation between editorial evaluation and revenue generation. See our full affiliate disclosure for details.
Primary data sources
We draw from established research databases and regulatory sources, never from marketing materials or manufacturer claims alone. Our primary sources include:
- PubMed / MEDLINE: The U.S. National Library of Medicine's database of peer-reviewed biomedical literature. Our primary source for clinical trial data and systematic reviews.
- Cochrane Library: Systematic reviews and meta-analyses considered the gold standard of evidence-based medicine.
- NIH Office of Dietary Supplements: Fact sheets and safety data on vitamins, minerals, and herbal supplements.
- FDA Safety Communications: Recalls, warning letters, and adverse event reports related to dietary supplements.
- Third-party certifiers: NSF International, USP (United States Pharmacopeia), Informed Sport, and ConsumerLab for independent purity and potency verification.
- Manufacturer COAs: Certificates of Analysis published by brands, cross-referenced against third-party testing data.
Update cadence
Reviews and rankings are updated quarterly, or sooner when new clinical evidence, product reformulations, or safety alerts warrant revision. Each article displays its most recent update date. Our research team monitors PubMed alerts, FDA safety communications, and manufacturer announcements on a rolling basis to ensure our content reflects the latest available evidence.