Peptides now span the widest evidence range of any molecular class in medicine — from insulin and semaglutide, among the most rigorously proven drugs ever approved, to compounds sold online with no human trials at all. Understanding Peptides is a free, 44-chapter textbook that explains the science behind that spectrum and, crucially, teaches you to tell the ends of it apart. Every peptide discussed carries an explicit evidence rating attached to a specific claim for a specific population, along with the reasoning behind it and the finding that would change it.
The book is science education, not a protocol manual. It contains no dosing, no reconstitution procedures, no injection technique, no cycles, and no vendor information — a deliberate design constraint. It is also neither an advertisement nor a debunking: semaglutide and insulin receive the strong ratings their trial data has earned, while compounds whose popular reputation outruns their human evidence are marked accordingly, with the animal literature taken seriously in both directions.
Part I builds the foundation — what peptides are, how they differ from proteins and small molecules, receptor signalling, the endocrine system, and pharmacokinetics. Part II covers metabolic peptides in depth, including GLP-1 and dual agonists, insulin, and the weight-loss compounds beyond them. Part III addresses growth and repair: growth hormone secretagogues, healing peptides, and the collagen and tissue-repair claims. Part IV covers neuropeptides and social peptides such as oxytocin and the appetite and mood signalling systems. Part V turns to clinical medicine — antimicrobial peptides, oncology, vaccines, and diagnostics. Part VI examines the technology: solid-phase synthesis, delivery and stability problems, oral formulations, and computational peptide design. Part VII synthesizes the evidence and teaches you to read a clinical trial yourself, and Part VIII covers the public landscape of regulation, compounding, marketing, sport, and access.
Written for readers who have heard about Ozempic and want the science rather than the headlines, for people in fitness and self-optimization who want evidence instead of forum consensus, for clinicians whose patients arrive with a list of compounds, and for biology, biochemistry, pharmacology, and nursing students. Fourteen appendices include a full peptide evidence table, an amino-acid reference, a guide to reading clinical trials, a red-flags checklist, a regulatory quick reference, and a glossary.