How the S to F tier board works.
Six evidence axes, a weighted score, and a letter. What the grade measures, and the two things it deliberately refuses to measure.
The tier board sorts every profiled compound from S to F. The letter is not a rating of how good a compound is, how popular it is, or how well it worked for anyone. It grades one thing: the strength of the published evidence behind it, weighted towards evidence in humans.
The six axes.
- Human evidence: how much controlled human data exists, weighted most heavily
- Preclinical depth: how thorough the animal and cell work is
- Mechanism confidence: how well the pathway is actually characterised rather than asserted
- Safety clarity: how well the safety profile is known, which is not the same as how safe it is
- Regulatory clarity: whether a regulator has actually reviewed the compound
- Practical relevance: whether the studied outcome is the one people care about
Each axis is scored from zero to five. They are kept separate on purpose, because the most common error in this field is letting a strong score on one axis stand in for another. A compound can have excellent mechanism confidence and no human evidence at all, and that combination is the single most important thing a reader can know.
How the axes become a letter.
The axes are combined into a weighted score out of 100 and mapped to a letter: S at 90 and above, A from 78, B from 65, C from 50, D from 35, and F below that. Two further inputs are derived rather than authored. Evidence consistency rewards findings that have been replicated. Claim risk is a penalty: when a compound is very widely discussed but thinly evidenced, the gap between what is said about it and what has been shown is itself a signal. Popularity can only ever lower a grade on PepCue. It can never raise one.
What a letter does not mean.
- An S does not mean safe for you, or appropriate for you
- An F does not mean the compound does nothing; it usually means nobody has properly tested it
- A grade is not a recommendation, and no grade implies you should take anything
A compound with no authored score is not given a letter at all. It appears in a review-pending group instead, because printing an unearned F would be inventing a value. Grades move when the evidence moves: a published trial, a new approval, a failed endpoint, or a withdrawn drug will change a letter, and the full scoring model is public so you can check our work.
FAQ.
What does an S tier mean on PepCue?
S tier means the published human evidence is unusually strong, typically large randomised trials and regulatory review. It is a statement about the evidence base, not about whether a compound is safe or appropriate for any individual.
Does an F grade mean a peptide does not work?
No. An F usually means there is little or no controlled human evidence either way. Unverified is not the same as disproven, and the tier board is explicit about that distinction.
If not, email kam@pepcue.app. For the shorter answers to the questions people ask most, see the FAQ.