Our Methodology
We assign every supplement a letter grade based on the certainty of the evidence. Our grading system evaluates:
- Quantity of evidence — How much research exists (none, low, medium, high)
- Quality of evidence — Study design and rigor (low, medium, high)
- Safety risks — Known adverse effects (none, low, medium, high, unknown)
- Efficacy grade (A-F) — Overall assessment of proven benefit
Grading Scale
| Grade | Meaning | Scientific Requirement |
|---|---|---|
| A | Highly likely/Proven Benefit | Multiple high-quality RCTs or systematic review showing consistent positive results |
| B | Probable Benefit | At least one well-designed RCT or several strong observational studies |
| C | Emerging / Inconclusive | Limited or low-quality studies and/or conflicting results |
| D | Weak | Based on expert opinion, case reports, or historical use without controlled testing |
| F | No benefit / Possible harm | High-quality studies failed to show benefit vs placebo, or harmful effects documented |
| n/a | Insufficient data | Incomplete data available to make evidence-based determinations |
How We Review
Our review process follows a systematic approach. For each substance or product, we:
- Search PubMed and other scientific databases for relevant studies
- Prioritize randomized controlled trials (RCTs) and systematic reviews
- Evaluate study quality, sample sizes, and potential biases
- Synthesize findings into an overall evidence grade
- Have findings reviewed by a veterinary specialist
Our reviews are updated as new research becomes available. Each review page shows when it was last updated so you can see how current the information is.