Functional classification system
Peptide nomenclature.
Carnosine and retatrutide are both peptides. So are insulin, oxytocin, and BPC-157. The word “peptide” tells you almost nothing about mechanism, evidence, or regulatory status. The field needs a working vocabulary.
The Peptide Association proposes a 12-category functional classification system to give this category a shared framework, organized by mechanism, not by marketing. Each category carries an evidence grade, a regulatory summary, and links to the compounds within it.
- Strong Evidence
- Large RCTs and/or FDA approval for a relevant indication.
- Moderate Evidence
- Clinical trial evidence without full FDA approval, or approved in 10+ countries.
- Limited Evidence
- Primarily preclinical data or small human studies.
- Emerging Evidence
- Early-stage human data, mechanistic rationale, or novel compounds in active development.
Contents
The 12 functional categories
Open any category for the full definition, mechanism, regulatory status, evidence assessment, and compound list.
- 01Metabolic GLP-AxisIncretin and amylin mimetics targeting appetite, insulin, and body weightStrong EvidenceSemaglutide, Tirzepatide, Retatrutide, Cagrilintide +1 more
- 02Regenerative / NO-ReceptorTissue repair and angiogenesis via nitric oxide and growth factor pathwaysLimited EvidenceBPC-157, TB-500, Thymosin Beta-4
- 03Thymic & ImmuneThymic hormone mimetics that regulate T-cell maturation and immune functionModerate EvidenceThymosin Alpha-1, Thymulin, Thyalin
- 04Bio-RegulatorsUltra-short tissue-targeted peptides that modulate gene expression and agingEmerging EvidenceEpitalon, Pinealon, Vilon, Cristagen +1 more
- 05GH SecretagoguesGHRH analogs and ghrelin mimetics that stimulate pituitary GH releaseModerate EvidenceSermorelin, Tesamorelin, CJC-1295, Ipamorelin +2 more
- 06Growth HormoneDirect GH receptor agonism via recombinant hGH and synthetic GH fragmentsStrong EvidenceRecombinant hGH (rhGH), AOD-9604
- 07Cosmetic & DermatologicSkin repair, collagen synthesis, and anti-inflammatory dermatologic peptidesModerate EvidenceGHK-Cu, KPV, Argireline
- 08Nootropic & CNSNeuropeptides targeting BDNF, anxiety, cognitive function, and neuroregenerationModerate EvidenceSemax, Selank, Cerebrolysin, Cortexin
- 09MitochondrialMitochondrially-encoded peptides targeting energy metabolism and cellular agingEmerging EvidenceMOTS-c, SS-31 (Elamipretide), Humanin
- 10Sexual FunctionCentral melanocortin and hypothalamic peptides for libido and sexual responseStrong EvidencePT-141 (Bremelanotide), Kisspeptin-10
- 11Visceral & MetabolicTargeted visceral adiposity reduction via GH-axis and NNMT pathway modulationModerate Evidence5-Amino-1MQ, Tesamorelin
- 12Sleep & CircadianPeptides that regulate sleep architecture, melatonin, and circadian entrainmentLimited EvidenceDSIP, Pinealon, Epitalon
How to use it
How to use this framework
This taxonomy is a reference tool, not a prescription guide. Here is how practitioners and patients get the most from it.
- 01
Start with the category, not the compound
Before researching a specific peptide, identify which functional category it belongs to. This tells you the mechanism, evidence grade, and regulatory environment before you read a single study.
- 02
Use evidence grades as a prior
Strong evidence categories (GLP-axis, Growth Hormone, PT-141) have RCT data and FDA approvals. Emerging categories (Mitochondrial, Sleep-Circadian) have compelling science but limited human trials. Grade your confidence accordingly.
- 03
Cross-category compounds are common
Tesamorelin appears in both GH Secretagogues and Visceral-Metabolic. Epitalon appears in Bio-Regulators and Sleep-Circadian. When a compound serves multiple functions, check both category pages.
- 04
Regulatory status shifts
BPC-157 compounding was affected by 2023 FDA guidance. Semaglutide compounding was restricted as supply normalized. Each compound's own profile carries its current US status; verify it with a licensed provider before clinical use.
Next step
Ready to discuss a specific protocol?
Understanding the taxonomy is the first step. A peptide-literate clinician can translate categories into a personalized protocol based on your labs, goals, and health history.
This taxonomy is an educational framework, not medical advice. Consult a qualified clinician before considering any peptide therapy. Regulatory status of individual compounds changes, verify current status with a licensed provider.