Peptide Classes, Explained

“Peptide” just means a short chain of amino acids — it’s a chemistry word, not a category of effect. The compounds people lump together span wildly different mechanisms and, more importantly, wildly different levels of evidence. This is a map of the main groups you’ll run into, with examples and what each is claimed to do. For the actual evidence on any single compound, open its profile — every one carries an evidence grade.

GLP-1 (and dual/triple) agonists

Examples: Semaglutide, Tirzepatide, Retatrutide.

These are incretin mimetics — they imitate gut hormones (GLP-1, and for the newer ones GIP and glucagon) that regulate blood sugar and appetite. They’re claimed for weight loss and glucose control.

This is the one group here with genuinely strong human evidence — semaglutide and tirzepatide are FDA-approved drugs backed by large trials. The catch worth repeating: the approved medicines are not the same thing as gray-market “research” vials of the same molecule, which carry the usual purity and identity questions.

Growth-hormone secretagogues

These aim to raise the body’s own growth hormone and IGF-1 rather than inject growth hormone directly. Two sub-families:

GHRH analogs mimic growth-hormone-releasing hormone — Sermorelin, CJC-1295, and Tesamorelin (the one FDA-approved member, for a narrow HIV-related indication).
GHRPs / ghrelin mimetics act on the ghrelin (GHS) receptor — Ipamorelin, GHRP-2 and GHRP-6, hexarelin; MK-677 (ibutamoren) is an oral non-peptide in the same lane.

Claimed for muscle, recovery, and “anti-aging.” Evidence is mostly preliminary or animal, with tesamorelin the narrowly-approved exception — and several are banned in sport.

”Healing” / repair peptides

Examples: BPC-157, TB-500 (a thymosin β4 fragment).

Marketed for tendon, ligament, muscle and gut repair. Both have large, encouraging animal literatures and essentially no human trials, and both are prohibited in tested sport — which is why they sit at “Animal only” on our scale.

Melanocortins

Examples: PT-141 / bremelanotide (FDA-approved for a specific sexual-desire disorder), Melanotan II (used for tanning).

These act on melanocortin receptors, which influence pigmentation and sexual function. PT-141 has real trial data for its narrow approved use; melanotan II is unapproved and carries notable safety concerns.

Nootropic peptides

Examples: Selank, Semax.

Short peptides developed in Russia (where some hold regional approvals), claimed for anxiety, focus, and cognition. The human data is small, mostly Russian, and weak, with little independent Western research.

Mitochondrial-derived peptides

Example: MOTS-c.

Peptides encoded in mitochondrial DNA, involved in metabolism and pitched for metabolic health, “longevity,” and performance. Evidence is animal-only, and MOTS-c is WADA-banned.

Other notable peptides

Thymosin Alpha-1 — an immune-modulating peptide, approved in some countries for specific conditions.
IGF-1 LR3 — a long-acting IGF-1 analog; the only approved IGF-1 product (mecasermin) treats a rare growth disorder.
GHK-Cu, Epitalon, DSIP, and AOD-9604 — cosmetic, “longevity,” sleep, and fat-loss peptides respectively, each resting on thin human evidence.

Bottom line

“Peptide” tells you about chemistry, not about whether something works. A handful — the GLP-1s, plus a few narrowly-approved drugs like tesamorelin and PT-141 — stand on real human trials. Most of the rest are preliminary or animal-only, and several are banned in sport. Match the hype first to the class, then to the specific compound’s evidence grade.

Educational content only. Not medical advice, and not an endorsement of using any unapproved substance.

Sources

Each linked compound profile carries its own primary citations.
FDA — approved labeling for semaglutide, tirzepatide, tesamorelin, bremelanotide, and mecasermin
WADA — The Prohibited List (peptide hormones, growth factors, and related classes)