A report describing outcomes in a small group of patients—useful for generating hypotheses but too weak to prove a treatment works.A case series is an uncontrolled, observational report of clinical outcomes in a group of patients receiving a treatment or sharing a diagnosis. Case series lack comparison groups, randomization, and blinding, placing them low in the evidence hierarchy. They are valuable for identifying rare adverse events, generating hypotheses, and reporting preliminary clinical observations. In peptide research, case series may represent the only human data available for compounds not yet in formal clinical trials—their limitations must be stated explicitly.