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Learn · Evidence grades

How to read the A–E grades

Every compound on this site carries an overall evidence grade — a single letter from A to E plus X for speculative. The grade reflects the quality of evidence supporting the compound's primary claimed effect, not whether the compound “works” in any colloquial sense.

The scale

A
Strong human RCT

Multiple high-quality randomized controlled trials in humans.

B
Limited human data

Pilot studies, observational data, or smaller RCTs.

C
Animal replicated

Effect demonstrated in multiple animal studies; human data sparse or extrapolated.

D
In vitro / mechanistic

Cellular or mechanistic evidence; little to no in-vivo data.

E
Anecdotal / community only

Reported use without published clinical evidence.

X
Speculative

No meaningful evidence for the specific claim being made.

What a grade does and doesn't say

A grade is about the evidence base, not about whether something is safe, appropriate for any specific person, or worth taking. A Grade A compound (strong human RCTs) may still be unsuitable for many people because of contraindications, side effects, or cost. A Grade D compound (mechanistic / in vitro only) may still be widely used by the community. Pair the grade with the candidate-profile and decision-framework sections at the bottom of every chapter.

Range grades

Section-level evidence tables sometimes show ranges like “B–C” or “C–D.” A range means different lines of evidence pull in different directions: e.g., topical evidence is strong (B) while injectable evidence is much weaker (C). The compound's overall grade is the editorial integration of all rows.

Independent replication

Evidence weight depends heavily on whether findings have been replicated outside the originating lab. Single-lab provenance is flagged explicitly because it's a known reliability concern in this space — compounds with hundreds of papers from one group and a handful of independent replications are very different from compounds with moderate volume across many groups.

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