Peptide basics

The most common phase for a peptide on this site is no phase at all

This page explains what trial phases mean and how the compounds tracked here are distributed across them. A phase describes the stage of testing reached, not whether a compound is effective or safe, and no dose or protocol appears here.

What each phase actually asks

Phase 1 asks whether a compound can be given to people at all, usually in small groups, watching for harm. Phase 2 asks whether it appears to do anything, in a few dozen to a few hundred people. Phase 3 asks whether it does that thing reliably in a large group, compared against placebo or an existing treatment. Phase 4 happens after approval and studies a product already on the market.¹²

The phases are cumulative in the sense that you rarely reach one without passing through the earlier ones, which is why the furthest phase a compound has reached is a compact summary of how much is known about it.²

The distribution across 68 compounds

• Phase 4 reached: 22 compounds.
• Phase 3 as the ceiling: 8 compounds.
• Phase 2 as the ceiling: 12 compounds.
• No phase recorded: 26 compounds, of which 25 have no registered trial at all.³

The shape is unusual. In most drug categories the numbers taper — many early trials, fewer late ones. Here the two ends are the largest groups, and the middle is thin. That is what a market looks like when a small number of heavily commercialised molecules sit alongside a long tail that never entered formal development.³

Why phase 4 is a stronger signal than it looks

Phase 4 is post-marketing research, so a compound can only reach it if a regulator approved a product containing it. A phase 4 record therefore implies the whole earlier sequence happened and a regulator reviewed the result.²

That makes phase 4 the most informative single label on this site. It is also why so few compounds carry it: reaching it requires a company to have taken a molecule the entire distance and a regulator to have agreed.²

What a stalled phase does and does not tell you

A compound stopping at phase 2 can mean the results were disappointing. It can equally mean the sponsor ran out of money, was acquired, or decided the market was too small. The registry records that testing stopped, not why.¹

So the correct reading of a phase 2 ceiling is narrow: this compound has been given to humans in a controlled setting, and nobody has run the larger trial that would settle whether it works.¹

Common questions