Evidence Grading Methodology
Every evidence claim on Peptide Treatments is assigned a grade from A to D based on the type, quality, and replication of supporting research. Grade A reflects strong clinical evidence from multiple human randomized controlled trials. Grade D reflects preclinical or theoretical rationale only. This methodology page defines each tier, explains how grades are assigned per indication, and lists the primary data sources used. Grades are reviewed when new studies are published and updated at least annually.
Four-Tier Evidence System
Each peptide-indication pair receives an independent grade. A peptide may hold a Grade A for one indication and a Grade C or D for another. Grades reflect the evidence available at the time of last review.
| Grade | Label | Qualifying Criteria | Typical Example |
|---|---|---|---|
| A | Strong Clinical Evidence |
| FDA-approved indications with robust trial data (e.g., semaglutide for type 2 diabetes and obesity) |
| B | Moderate Clinical Evidence |
| Off-label use with supporting clinical trial data or strong observational cohorts |
| C | Emerging Evidence |
| Research-phase peptides with early human safety data but no completed efficacy trials |
| D | Preclinical / Theoretical |
| Novel research peptides with promising animal data but absent human trial data |
Grading Methodology
Per-Indication Grading
Evidence grades are assigned per peptide-indication pair, not per peptide globally. A single peptide is graded independently for each condition it is studied for. This prevents misleadingly high grades from spilling over from well-studied uses to speculative ones.
Study Design Hierarchy
RCTs with blinding and placebo controls rank highest. Cohort studies and case-control designs rank next. Cross-sectional studies, case series, and expert opinion rank lowest among human evidence. Systematic reviews and meta-analyses are weighted by the quality of the constituent studies, not simply their existence.
Human vs. Animal Evidence Weighting
Human evidence is categorically required for Grades A and B. Animal or in vitro data can contribute supporting mechanistic rationale at those tiers but cannot substitute for clinical data. For Grade C, human pilot data must be present even if the sample size is small. Grade D is the only tier where animal-only evidence is sufficient to justify a claim.
Replication Requirement
Grade A requires consistent findings across at least two independent research groups or trial sites. A single large RCT, even if well-designed, is sufficient only for Grade B unless independently replicated. Discordant findings across studies are noted in the evidence summary and may result in a grade downgrade pending resolution.
Recency Weighting
Studies published within the last five years receive full weight. Studies from five to ten years ago are included but flagged for potential supersession by newer data. Studies older than ten years are included as historical context only and do not independently support a high-tier grade unless no newer evidence contradicts them.
Regulatory Status as a Signal
FDA approval for a specific indication is treated as corroborating evidence for Grade A, but not as a standalone requirement. A peptide can receive Grade A on the strength of peer-reviewed evidence alone. Conversely, FDA approval status in other jurisdictions (EMA, Health Canada, TGA) is noted but does not automatically elevate the U.S.-relevant grade.
Primary Data Sources
All evidence claims are sourced from publicly accessible, peer-reviewed, or regulatory databases. We do not rely on manufacturer-provided data or gray literature as primary evidence.
PubMed / MEDLINE
Primary database for peer-reviewed biomedical literature. All cited studies are verified against PubMed records.
ClinicalTrials.gov
Registry of completed, active, and planned clinical trials. Used to verify trial phase, enrollment, and outcomes.
ChEMBL
Bioactivity database for drug-like molecules. Provides mechanistic and pharmacological context for peptide compounds.
Open Targets Platform
Target-disease association evidence. Used to assess the strength of molecular evidence linking peptides to conditions.
DrugBank
Comprehensive drug and drug-target database. Provides pharmacokinetic, interaction, and approval status data.
FDA FAERS
FDA Adverse Event Reporting System. Used to identify post-market safety signals for approved peptide therapies.
Limitations
- Evidence grades reflect the literature available at the time of last review and may lag recent publications.
- Publication bias in the scientific literature may overrepresent positive findings, which can inflate perceived evidence strength.
- Many peptide studies are conducted in populations that differ from general clinical patients (e.g., athletes, specific disease cohorts), limiting generalizability.
- Grading is performed by content reviewers, not a formal systematic review panel. Grades should be interpreted as informed assessments, not official clinical guidelines.
- This system does not assess individual patient appropriateness. Evidence grades are population-level signals, not personal medical recommendations.
- Off-label and compounded uses are not endorsed by this grading system — grades describe the evidence base only.