Therapeutic Peptides: An Evidence-Tiered Survey Across Neuroplasticity, Anti-Ageing, Fitness, and Tissue Repair: A Critical Review

The peptide pharmacology landscape is extensive and heterogeneous in evidence quality. This review surveys twenty therapeutic peptides and peptide-class compounds across four clinical domains --- neuroplasticity and cognition, anti-ageing, fitness and growth, and tissue repair --- using a four-tier evidence framework that distinguishes approved compounds with large randomised trial evidence from compounds with credible but non-Western evidence, pre-clinical candidates, and speculative compounds awaiting human investigation. Among Tier~1 agents, semaglutide and tirzepatide provide the reference standard for rigorous peptide evidence. In the neuroplasticity domain, Semax and Selank are the most credible non-prescription neuropeptides, with a Russian randomised controlled trial evidence base uncommon in unregulated pharmacology. Thymosin Alpha-1 has the strongest clinical evidence of any immunomodulatory peptide surveyed, approved in approximately 35~countries. Most compounds popular in fitness and longevity communities --- BPC-157, TB-500, Ipamorelin, Epitalon --- sit at Tier~3 or Tier~4, with compelling animal data and insufficient human evidence to support clinical recommendation. Non-pharmacological interventions, particularly aerobic exercise and sleep, retain the strongest and most consistent human evidence for neuroplasticity, and no peptide reviewed here surpasses them on this metric. The paper provides a practical navigational framework for a compound class in which the distance between pharmacological promise and clinical evidence is frequently substantial and rarely clearly labelled.