A comprehensive review of injectable peptides in sports medicine reveals a stark disconnect between clinical adoption and scientific evidence. Among five peptide classes examined from 2020-2025 research, only glucagon-like peptide-1 receptor agonists like semaglutide demonstrated reproducible benefits for knee osteoarthritis, primarily through weight loss rather than direct tissue repair. Collagen-derived preparations showed modest postoperative recovery benefits in limited studies, while regenerative peptides including BPC-157 and thymosin derivatives remain entirely investigational. This evidence gap represents a concerning trend in sports medicine where promising mechanisms drive clinical use before rigorous validation. The widespread adoption of unproven peptides poses multiple risks: uncertain efficacy, variable product quality from compounding pharmacies, unknown long-term safety profiles, and potential antidoping violations for competitive athletes. The review's Level V evidence rating and predominantly C-grade recommendations underscore how thin the scientific foundation remains. For practitioners, this analysis suggests extreme caution with off-label peptide use outside established metabolic indications. The field needs controlled trials examining tissue-specific outcomes rather than relying on mechanistic rationale alone. Until then, most injectable peptides represent expensive experimental treatments with more theoretical promise than clinical proof.