Peptide Classes, Explained

The word “peptide” just means a short chain of amino acids (the building blocks that make up proteins). It’s a chemistry word — it tells you what something is, not what it does. So the compounds people group together under this one label actually work in very different ways. And, just as important, some have strong proof behind them while others have almost none.

Think of this page as a map. It walks through the main groups you’ll come across, gives a few examples of each, and says what people claim it does. To see the actual proof for any single compound, open its own profile — every one comes with an evidence grade (our rating of how strong the evidence is).

GLP-1 (and dual/triple) agonists

Examples: Semaglutide, Tirzepatide, Retatrutide.

These copy hormones your gut naturally makes after you eat — hormones (called GLP-1, and for the newer ones GIP and glucagon) that help control blood sugar and how hungry you feel. Because of that, they’re used for weight loss and to manage blood sugar.

This is the one group on this page with genuinely strong proof in people. Semaglutide and tirzepatide are FDA-approved medicines, backed by large studies. One thing worth saying again, though: an approved medicine is not the same as a “research” vial of the same molecule sold on the gray market. Those vials raise the usual questions about whether they’re pure, and whether they even contain what the label says.

Growth-hormone secretagogues

These try to nudge your body into making more of its own growth hormone (and a related signal called IGF-1), rather than injecting growth hormone straight in. There are two sub-groups:

• GHRH analogs copy a natural signal called growth-hormone-releasing hormone — Sermorelin, CJC-1295, and Tesamorelin (the only FDA-approved one, and only for a narrow HIV-related use).
• GHRPs / ghrelin mimetics act on the ghrelin receptor (ghrelin is the “hunger hormone”) — Ipamorelin, GHRP-2 and GHRP-6, hexarelin; MK-677 (ibutamoren) is a pill that isn’t technically a peptide but works in the same way.

People take these hoping for more muscle, faster recovery, and “anti-aging.” Most of the evidence is still early-stage or comes from animal studies, with tesamorelin being the one narrow exception that’s approved. Several of these are also banned in tested sports.

”Healing” / repair peptides

Examples: BPC-157, TB-500 (a piece of a protein called thymosin β4).

These are sold for repairing tendons, ligaments, muscle, and the gut. Both have a lot of promising research — but it’s almost all in animals, with only small human pilot signal. Both are also banned in tested sports. That’s why we grade them 4 (Animal-leaning) on the Codex Scale — short of “Animal only” thanks to the pilot work, but well below any meaningful human evidence.

Melanocortins

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

These act on receptors (the “docking spots” on cells) that affect skin color and sexual function. PT-141 has real study data for its one approved use. Melanotan II is not approved and comes with real safety worries.

Nootropic peptides

Examples: Selank, Semax.

These are short peptides first developed in Russia (where a few are approved regionally). They’re claimed to help with anxiety, focus, and thinking. The human evidence is small, mostly Russian, and weak, with little independent research outside of Russia to back it up.

Mitochondrial-derived peptides

Example: MOTS-c.

These are peptides made from the DNA inside your mitochondria (the parts of your cells that produce energy). They play a role in metabolism, and they’re pitched for metabolic health, “longevity,” and performance. The evidence is animal-only, and MOTS-c is banned by WADA (the World Anti-Doping Agency).

Other notable peptides

• Thymosin Alpha-1 — a peptide that adjusts how the immune system works; approved in some countries for certain conditions.
• IGF-1 LR3 — a long-lasting version of IGF-1; the only approved IGF-1 product (mecasermin) is for a rare growth disorder.
• GHK-Cu, Epitalon, DSIP, and AOD-9604 — used for skin/cosmetic, “longevity,” sleep, and fat loss, in that order. Each one rests on thin human evidence.

Bottom line

The word “peptide” tells you about chemistry, not about whether something actually works. A few — the GLP-1s, plus a couple of narrowly-approved drugs like tesamorelin and PT-141 — stand on real human studies. Most of the rest are early-stage or animal-only, and several are banned in sports. So when you hear a big claim, check it twice: first against the class it belongs to, then against that 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)