Peptide Classes: A Practical Taxonomy for Research

Research peptides are typically classified by the receptor system they engage or by the biological pathway they investigate. This taxonomy is loose — many peptides span categories — but it is the working framework most laboratories use. This article walks through the major classes with example compounds and the receptors they target.

Incretin and metabolic peptides

The fastest-growing class. GLP-1 receptor agonists (Semaglutide), dual GLP-1 / GIP agonists (Tirzepatide), and triple GLP-1 / GIP / glucagon agonists (Retatrutide) define the contemporary research frontier. All three are 31–39 residue peptides with fatty-acid modifications for extended half-life. See our deeper review of triple agonism and the underlying receptor biology.

Tissue and signalling peptides

BPC-157 (a 15-residue pentadecapeptide) and TB-500 (a Thymosin Beta-4 fragment) are the most-studied. Both are investigated in tissue remodelling, angiogenesis, and growth-factor signalling research, but through distinct molecular pathways. See our comparative analysis.

Growth hormone secretagogues

Compounds acting on the ghrelin (GHS-R1a) or GHRH receptor systems. Includes pentapeptides like Ipamorelin (selective GHS-R1a agonist) and modified GHRH(1-29) analogues like CJC-1295. Used to probe pituitary somatotroph signalling and growth hormone axis dynamics in preclinical research.

Melanocortin peptides

Cyclic lactam analogues of α-melanocyte-stimulating hormone (α-MSH) such as MT-2. Investigated in MC1R / MC4R / MC5R receptor binding studies. The cyclic structure is critical — linear analogues are rapidly degraded and show reduced receptor selectivity.

Neuropeptides

Synthetic ACTH-derived peptides such as Semax (the heptapeptide Met-Glu-His-Phe-Pro-Gly-Pro). Investigated in BDNF expression studies, dopaminergic signalling research, and serotonergic system modulation in preclinical models.

Copper peptide complexes

GHK-Cu — a tripeptide-copper coordination complex (Gly-His-Lys with bound Cu²⁺). Investigated in gene expression modulation and extracellular matrix remodelling research. The copper coordination is functionally essential; the apo-tripeptide is a different molecule with different activity.

Where this taxonomy breaks down

The classes overlap. BPC-157 has been investigated in CNS contexts as well as peripheral tissue. Melanocortin agonists have metabolic effects through MC4R. The classification is a starting point for experimental design, not a strict ontology.

For the full Pillar Research catalogue across all classes, see our compound catalogue.