Types of Peptides: A Map of the Six Main Classes.

How peptides are classified

Biochemists classify peptides several ways: by origin (endogenous vs. synthetic), by length, by structure (linear vs. cyclic), by source (natural vs. engineered), and by function. For researchers and end users, function is the most useful lens. It's also the one the literature uses most often.

If you're new to peptides, start with the functional classes below and work outward. We link to detailed standalone guides for each peptide. If you haven't yet, read What Are Peptides? first — it covers the basic science this article assumes.

Class 1: Healing & repair peptides

These are peptides whose research signal is around tissue repair — gut lining, muscle, tendon, ligament, skin, cartilage, vascular tissue. Mechanisms vary, but the common theme is that they influence inflammatory, angiogenic (blood-vessel-forming), or cellular-migration pathways that the body uses to heal an injury.

• BPC-157 — a 15-amino-acid fragment from a protein in gastric juice. Heavy rat literature on gut, tendon and wound healing. Full guide →
• TB-500 (Thymosin Beta-4 fragment) — tissue repair signalling molecule; cardiac and soft-tissue repair research. Full guide →
• GHK-Cu — copper-binding tripeptide. Skin remodelling, wound healing, fibroblast stimulation. Full guide →

Who researches these? Investigators in musculoskeletal medicine, gastroenterology, dermatology and regenerative biology. What they share is a slow onset of any observed effect (weeks, not hours) and animal-data-rich, human-data-light profiles.

Class 2: Growth-hormone secretagogues (GHS)

Growth hormone (GH) is itself a protein. But the peptides in this class don't replace GH — they trigger its release from the pituitary, preserving the body's natural pulsatile rhythm. Two subfamilies dominate:

• GHRH analogs — mimic growth-hormone-releasing hormone. Examples: Sermorelin, CJC-1295 (no DAC), Tesamorelin.
• GHRPs / Ghrelin mimetics — activate the ghrelin (GHS-R1a) receptor. Examples: GHRP-2, GHRP-6, Hexarelin, Ipamorelin.

They're often stacked — a GHRH analog alongside a ghrelin mimetic — because the two pathways act synergistically on the pituitary. The classic pairing is CJC-1295 (no DAC) with Ipamorelin.

Researched applications: age-related GH decline, body composition, sleep quality, muscle recovery. Only Tesamorelin has regulatory approval — for HIV-associated lipodystrophy.

Class 3: Metabolic & obesity peptides (GLP-1 and beyond)

This is the class reshaping medicine right now. GLP-1 (glucagon-like peptide-1) is an incretin — it triggers insulin release and slows gastric emptying. Analogs of GLP-1 and its sister hormones have become blockbuster weight-loss and diabetes drugs.

• Single agonists — Semaglutide (Ozempic, Wegovy), Liraglutide (Victoza). GLP-1 only.
• Dual agonists — Tirzepatide (Mounjaro, Zepbound). GLP-1 + GIP.
• Triple agonists — Retatrutide. GLP-1 + GIP + glucagon. Currently the most potent in this class in late-phase trials.

These peptides work on pathways regulating appetite, satiety and energy expenditure. Phase 3 retatrutide data at 12 months has reported weight loss around 22–24% of baseline body weight at the top doses — numbers that would have been considered implausible a decade ago.^[1]

Class 4: Mitochondrial peptides

Mitochondria — the "powerhouses" — turn out to have their own small genome that encodes a few short peptides. These "mitochondrial-derived peptides" (MDPs) are a newer, smaller class with an interesting theoretical profile: they act inside the cell on metabolism itself rather than on external receptors.

• MOTS-C — 16 amino acids. Implicated in insulin sensitivity, metabolic flexibility, and aspects of exercise physiology. Full guide →
• Humanin — 24 amino acids. Studied in Alzheimer's models and metabolic stress.
• SHLP family — Small Humanin-Like Peptides. Early research.

This class is young. Nearly all the evidence is pre-clinical. Worth watching, not yet worth betting on.

Class 5: Cognitive & neurogenic peptides

Short peptides with reported effects on brain-derived neurotrophic factor (BDNF), nerve growth factor (NGF), and neurotransmitter systems. Much of the primary literature on this class is Russian; translation quality and methodology vary.

• Semax — an ACTH fragment analog, registered as a nootropic in Russia; BDNF and dopamine modulation.
• Selank — a TFF (tuftsin) analog, researched for anxiolytic properties.
• Cerebrolysin — technically a mix of peptides/amino acids from porcine brain; used clinically for stroke and neurotrauma in parts of Europe and Asia.
• Dihexa — an angiotensin IV analog, pre-clinical BDNF interest.

Class 6: Cosmetic peptides

Peptides formulated for topical application, with effects that range from well-documented to marketing-copy-deep. The best-researched:

• GHK-Cu — crosses into this class from Class 1. Pro-collagen effects are reasonably well-supported. Full guide →
• Matrixyl (Palmitoyl Pentapeptide-4) — collagen I signalling.
• Argireline (Acetyl Hexapeptide-8) — marketed as a topical Botox alternative; in vivo evidence modest.
• Copper peptides generally — beyond GHK-Cu, the broader copper-peptide family has wound-care and hair-follicle research.

Why the classes overlap

A few peptides sit across boundaries and that's not a classification failure — it's biology. GHK-Cu is both a healing peptide (wound repair, scar reduction) and a cosmetic peptide (collagen, pigmentation). Tesamorelin is a GH secretagogue whose approved indication is metabolic (visceral fat reduction). BPC-157 is classified as healing but has reported effects on dopaminergic and serotonergic pathways that could arguably place it in cognitive research too.

Don't overweight the taxonomy. Use it as a memory aid. The honest way to evaluate any peptide is: what specific receptor or pathway does it act on, what's the published evidence for that action in the species you care about, and what's the risk/benefit balance? That question is the same no matter what class the molecule sits in.