Literature Depth Index

Each tier describes the published literature on a compound: how much of it there is, how many independent groups produced it, and which model it was done in, from controlled studies in humans to animal models, cell culture and binding assays. A tier is a statement about publications. It says nothing about what any study found, and it is not a recommendation for or against any compound.

Tiers run from A (an extensive controlled literature from many independent groups) to F(little or no literature specific to the compound). The column beside each name is the compound's receptor or structural class, stated in molecular terms, or “Class not stated” where no class can be given without inventing one.

For a compound's structure, sequence and certificates, see its compound hub. The researcher's guide to peptides covers the fundamentals this index is read against.

Four properties of the literature decide a tier: (1) volume, the number of peer-reviewed publications on the compound itself rather than on a related molecule; (2) model, whether the work was done in controlled human studies, in animal models, or in cell culture and binding assays; (3) design, whether studies were randomised and controlled; and (4) replication, whether independent laboratories produced the same kind of data.

The model carries the most weight, because it is the one property a reader cannot infer from a citation count. A compound with a large animal literature and no controlled human study is placed in tier D however many papers it has.

Assignments are checked against PubMed and ClinicalTrials.gov and moved when the literature moves. A compound's hub lists its structure and the certificates for its batches.

The literature on research peptides is very uneven. A few receptor agonists, the GLP-1 receptor agonists among them, have very large published literatures produced by long industrial programmes, while many short research peptides have a handful of papers from one or two laboratories.

Publication bias applies throughout: a study that found something is more likely to be published than one that did not, so a large literature is not the same thing as a settled one. A tier records the shape of what has been published and should be read alongside the primary papers.

The glossary defines the analytical terms used across the library, and the storage and handling guide covers stability in solution.