A study that follows a defined group of people over time to see what happens to them—observational, not experimental.A cohort study follows a group of individuals sharing a common characteristic (exposure, treatment, condition) over time, measuring outcomes prospectively or retrospectively. Unlike RCTs, cohort studies are observational and cannot establish causation, but they can identify associations and generate hypotheses. In peptide research, cohort data from self-experimentation communities provides real-world exposure information but lacks the controls, blinding, and standardization of clinical trials.