In short
Evidence grade is this site's letter rating (A through D) of how strongly human clinical data supports a given compound or therapy, assigned strictly on the basis of human study results rather than animal or cell-culture data.
The grading system used across this site's compound, peptide, and therapy pages is deliberately conservative about what moves a compound up the scale: only human evidence lifts a grade, and animal or in-vitro data — however promising or mechanistically compelling — is noted as context or as an explanation for why a compound is being studied, but never used to justify a higher grade than the human data supports on its own.
Grade A ("Established") requires repeated human randomized trials showing benefit on outcomes that matter clinically, not just biomarker changes — this is a genuinely high bar that most compounds and supplements marketed for longevity do not meet. Grade B ("Promising") covers compounds with real human trial data showing measurable biomarker or functional effects, where longer-term outcome data is still missing. Grade C ("Early") is animal or small human pilot data only, without dependable controlled human evidence yet. Grade D ("Insufficient or unsafe") covers compounds with no credible human evidence supporting the claimed use, or where known risks outweigh what benefit evidence exists.
This grading exists because marketing claims for longevity products routinely blur the line between "shown to work in a petri dish or a mouse" and "shown to work in a person," and this glossary and the rest of this site treat that distinction as load-bearing throughout — a compound's grade should always be read alongside its stated evidence gap (what hasn't been shown yet), not as a standalone verdict divorced from that context.
Where this shows up on the site
Frequently asked questions
Does a Grade C compound mean it doesn't work?
No — it means the human evidence needed to confirm whether it works, at what dose, and how safely, hasn't been generated yet. It's a statement about the current state of evidence, not a verdict that the compound is ineffective.
Can animal data ever earn a compound a Grade A?
No. Grade A requires repeated positive human randomized trials on outcomes that matter clinically. Animal and in-vitro data are cited as mechanistic context only and never lift the grade on their own.