Peptides are marketed for everything from injury recovery to longevity, but most lack human evidence and clear mechanisms—here's how to separate legitimate science from hype. Peter Attia presents a framework for evaluating individual peptides, examining BPC-157 and CJC-1295 as case studies, and explaining why gray-market versions lack the manufacturing controls and safety data of FDA-approved drugs. A peptide is simply a short chain of amino acids; the word tells you nothing about safety or efficacy—you must evaluate each molecule individually using five critical questions about mechanism, human evidence, dosing, risk-benefit, and available alternatives.