Grade A Strong Evidence
Evidence strength 4 out of 4.High-quality studies show consistent, clinically meaningful benefit with an acceptable safety profile.
How We Grade Evidence
Our ratings are based on the quality, quantity, and consistency of scientific evidence, not opinions, tradition, or marketing. We follow a transparent, reproducible process so you can trust every recommendation.
Our Evidence Grading Process
Every supplement, food, or topic goes through the same rigorous evaluation.
- 1. Identify & Gather Systematically search for all relevant, high-quality studies and data.
- 2. Assess Quality Evaluate study design, risk of bias, sample size, and overall quality.
- 3. Evaluate Consistency Determine whether results are consistent across multiple studies.
- 4. Assess Safety Review safety data, adverse events, and contraindications.
- 5. Determine Grade Integrate all evidence factors to assign an overall A–F grade.
Evidence Grading Scale
Overall grades reflect the strength of evidence for benefit and safety.
Grade B Moderate Evidence
Evidence strength 3 out of 4.Moderate-quality evidence suggests benefit, but additional research could affect confidence or conclusions.
Grade C Limited Evidence
Evidence strength 2 out of 4.Limited or lower-quality studies suggest possible benefit, but evidence is insufficient or inconsistent.
Grade D Weak Evidence
Evidence strength 1 out of 4.Low-quality or very limited studies show little to no benefit, or results are largely inconsistent.
Grade F No Evidence / Risk
Evidence strength 0 out of 4.No reliable studies demonstrate benefit, or there is a significant risk of harm.
Grades apply to the specific use and species evaluated. New high-quality evidence may change a grade over time.
We Evaluate Four Key Areas of Evidence
Evidence Quantity
The number of studies available on the topic or product.
Evidence Quality
How well the studies are designed, conducted, and reported.
Evidence of Benefit
The degree to which studies show a positive effect in pets.
Safety Concerns
The risk of adverse effects or safety concerns reported in the evidence.
Multiple veterinarians and subject-matter specialists independently evaluate the evidence. Grades are assigned only when there is agreement among our reviewers.
Frequently Asked Questions
Why don't you include expert opinions or anecdotes?
Opinions and anecdotes can be useful starting points, but they cannot reliably demonstrate benefit. Our grades reflect the published scientific evidence.
Why do some popular supplements receive low grades?
Popularity does not establish effectiveness. A low grade means the available research does not yet show a clear, reliable benefit or raises a meaningful safety concern.
Why don't you use “A+” or “A−” grades?
We use a simple A–F scale so grades remain clear and comparable. Plus and minus grades would imply more precision than the underlying evidence can support.
How often are grades updated?
Reviews are living resources. When meaningful new research is published, our reviewers reassess the evidence and revise grades when appropriate.
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