Evidence Grading System

How we evaluate research quality and assign evidence grades to supplements.

Not all scientific evidence is created equal. A single promising test-tube study is very different from multiple well-designed human trials. Our evidence grading system helps you quickly understand the strength of research behind each supplement.

We use two complementary systems: Evidence Grades for overall product quality, and Study Level Classifications for individual research papers.

Evidence Grades (A-D)

Each product receives an overall evidence grade based on the quality, quantity, and consistency of human research.

Grade A: Strong Evidence

Multiple high-quality randomized controlled trials (RCTs) with consistent positive results. Effect sizes are clinically meaningful. Research conducted by independent groups. Established safety profile.

Requirements:

• At least 3 independent, well-designed RCTs
• Total sample size > 300 participants
• Consistent findings across studies
• Appropriate dosing and duration
• Replicated by independent research groups

Interpretation: You can be reasonably confident this supplement works for its primary indication when used appropriately.

Grade B: Good Evidence

Some well-designed RCTs or strong observational evidence showing benefit. Results are generally positive but may have limitations. More research would be helpful but current evidence is promising.

Requirements:

• 1-2 well-designed RCTs with positive results
• OR multiple high-quality cohort/observational studies
• Sample sizes adequate but not extensive
• Some minor study limitations present
• Biological plausibility supported

Interpretation: Evidence is encouraging and suggests benefit, though more research would strengthen confidence.

Grade C: Preliminary Evidence

Limited human data or mixed results. May include small pilot studies, inconsistent findings, or primarily animal/in vitro research. Shows promise but significant uncertainty remains.

Requirements:

• Small pilot studies with promising results
• OR inconsistent findings across studies
• OR primarily animal/in vitro evidence
• Limited sample sizes (< 100 participants total)
• Mechanistic rationale exists but clinical data limited

Interpretation: Interesting but preliminary. Consider this experimental rather than established.

Grade D: Insufficient Evidence

Very limited or conflicting human evidence. May have theoretical basis but lacks clinical support, or studies show no benefit. Insufficient data to make recommendations.

Requirements:

• Only test-tube or animal studies available
• OR human studies show no benefit
• OR evidence is severely conflicting
• Poor study quality or methodology

Interpretation: Not enough evidence to recommend. Wait for better research.

Study Level Classifications

Individual studies in our research library are classified by their design and evidence quality.

RCT

Randomized Controlled Trial (RCT)

The gold standard for clinical research. Participants are randomly assigned to receive either the intervention or a placebo/control. Ideally double-blinded.

Strength: Minimizes bias and establishes causation

Meta-Analysis

Meta-Analysis / Systematic Review

Combines data from multiple studies to increase statistical power and identify patterns. Provides overview of entire research landscape.

Strength: Synthesizes all available evidence, highest level when well-conducted

Cohort Study

Cohort / Observational Study

Follows groups of people over time but without randomization. Can identify associations but harder to prove causation.

Strength: Useful for long-term outcomes and real-world effectiveness

Case Series

Case Report / Case Series

Detailed reports of individual patients or small groups. Hypothesis-generating but not conclusive.

Strength: Can identify rare effects or generate research questions

In Vitro

In Vitro (Test Tube) Study

Laboratory research using cells or biological molecules. Shows mechanisms but doesn't always translate to humans.

Strength: Explores mechanisms but low clinical relevance alone

Animal Study

Research conducted in animals (mice, rats, etc.). Important for safety testing and mechanism exploration but limited human applicability.

Strength: Bridges lab and human research but many findings don't replicate

Critical Factors in Study Quality

Beyond study design, we evaluate these quality markers:

Strong Indicators

• Double-blind, placebo-controlled design
• Adequate sample size (power calculation)
• Appropriate duration for outcome
• Independent funding (no industry bias)
• Pre-registered protocol
• Published in peer-reviewed journal

Red Flags

• Industry-funded with no independent replication
• Very small sample size (< 20 per group)
• Short duration inadequate for outcome
• Multiple outcomes tested (p-hacking risk)
• Conflicts of interest not disclosed
• Published in predatory journal

Understanding Limitations

Every study has limitations. We explicitly call these out because transparency matters more than hype. Common limitations include:

Sample size: Small studies (< 50 participants) may miss real effects or find false positives
Duration: Short studies may not capture long-term benefits or risks
Population: Studies in elderly men may not apply to young women
Dosing: Tested dose may differ from commercially available products
Single-center: Results from one location may not generalize broadly
Funding source: Industry-funded research deserves extra scrutiny

The Bottom Line

Evidence grading isn't about perfection—it's about honest assessment. A "Grade B" supplement with good evidence may be more worth trying than a "Grade A" pharmaceutical with serious side effects. Our job is to give you the clearest possible picture of what the research actually shows.

When in doubt, look at the full body of evidence, not just one study. And always discuss supplements with your healthcare provider, especially if you have medical conditions or take medications.