What Are Peptide Hormones? A Complete List of Every Peptide Hormone in the Human Body and What They Do

Peptide hormones are the body's chemical messengers — short chains of amino acids released by glands and tissues that travel through the bloodstream to regulate distant target cells. They control growth, metabolism, reproduction, stress responses, appetite, sleep, immune function, blood pressure, and pain perception. Understanding peptide hormones is the foundation for understanding peptide research, because every research peptide is either a natural peptide hormone, a fragment of one, or an analog designed to mimic one.

How Peptide Hormones Work

Unlike steroid hormones (testosterone, estrogen, cortisol) that cross cell membranes and act on intracellular receptors, peptide hormones are water-soluble and cannot penetrate lipid cell membranes. Instead, they bind to receptors on the cell surface, triggering intracellular signaling cascades (second messenger systems like cAMP, calcium, or IP3) that alter cell behavior without the hormone itself entering the cell. This surface-receptor mechanism is why peptide hormones typically act faster than steroid hormones (seconds to minutes vs hours to days) but have shorter durations of effect.

Peptide hormones are synthesized as larger precursor proteins (preprohormones), processed through enzymatic cleavage in the endoplasmic reticulum and Golgi apparatus, stored in secretory granules, and released by exocytosis when the appropriate stimulus arrives. This synthesis-storage-release system allows rapid hormone secretion in response to physiological signals.

Complete List of Major Peptide Hormones

Hypothalamic Peptide Hormones

The hypothalamus produces releasing and inhibiting hormones that control the pituitary gland. Growth Hormone Releasing Hormone (GHRH, 44 amino acids) stimulates GH release — Sermorelin, CJC-1295, and Tesamorelin are synthetic GHRH analogs used in research. Somatostatin (14 amino acids) inhibits GH release. Gonadotropin-Releasing Hormone (GnRH, 10 amino acids) controls reproductive hormones — kisspeptin acts upstream of GnRH. Corticotropin-Releasing Hormone (CRH, 41 amino acids) drives the stress response. Thyrotropin-Releasing Hormone (TRH, 3 amino acids) controls thyroid function. And Orexin/Hypocretin (33 and 28 amino acids) controls the sleep-wake cycle.

Pituitary Peptide Hormones

The pituitary gland translates hypothalamic signals into systemic hormones. Growth Hormone (GH, 191 amino acids) drives growth and metabolism — CJC-1295, Ipamorelin, GHRP-2, GHRP-6, and Hexarelin all stimulate its release. Adrenocorticotropic Hormone (ACTH, 39 amino acids) stimulates cortisol production — Semax is derived from ACTH(4-7). Oxytocin (9 amino acids) drives social bonding, wound healing, and muscle regeneration. Vasopressin/ADH (9 amino acids) controls water balance and blood pressure. And Prolactin (199 amino acids) drives milk production and influences immune function.

Pancreatic Peptide Hormones

The pancreas produces the hormones that control blood sugar. Insulin (51 amino acids) lowers blood glucose — the most famous peptide hormone. Glucagon (29 amino acids) raises blood glucose — retatrutide activates the glucagon receptor. Amylin (37 amino acids) slows gastric emptying and suppresses glucagon. Pancreatic Polypeptide (PP, 36 amino acids) reduces appetite after meals. And Somatostatin is also produced by pancreatic delta cells, inhibiting both insulin and glucagon.

Gut Peptide Hormones

The gastrointestinal tract is the body's largest endocrine organ. GLP-1 (30 amino acids) enhances insulin secretion and suppresses appetite — semaglutide and tirzepatide target the GLP-1 receptor. GIP (42 amino acids) enhances insulin secretion — tirzepatide and retatrutide also activate GIP receptors. PYY (36 amino acids) suppresses appetite after meals. Ghrelin (28 amino acids) stimulates appetite and GH release — GHRPs mimic ghrelin's GH-releasing effect. Cholecystokinin (CCK, variable length) triggers digestive enzyme release and satiety. Vasoactive Intestinal Peptide (VIP, 28 amino acids) regulates motility, secretion, and immune function. Neurotensin (13 amino acids) modulates fat absorption and dopamine signaling. And BPC-157 (15 amino acids) — a peptide isolated from gastric juice — is one of the most researched gastroprotective peptides.

Cardiovascular Peptide Hormones

The heart and vascular system produce peptide hormones for blood pressure regulation. Atrial Natriuretic Peptide (ANP, 28 amino acids) and B-type Natriuretic Peptide (BNP, 32 amino acids) reduce blood volume and pressure. Endothelin (21 amino acids) is the most potent vasoconstrictor known. Apelin (variable length, typically 13-36 amino acids) strengthens cardiac contraction and dilates blood vessels. And Calcitonin Gene-Related Peptide (CGRP, 37 amino acids) is a potent vasodilator involved in migraine.

Thymic Peptide Hormones

The thymus produces peptides that regulate immune cell development. Thymosin Alpha-1 (28 amino acids) modulates immune function and is approved in 35+ countries. Thymulin (9 amino acids) requires zinc for activity and promotes T-cell maturation. And Thymosin Beta-4 (43 amino acids) — the parent molecule of TB-500 — regulates cell migration, wound healing, and inflammation.

Other Peptide Hormones

Calcitonin (32 amino acids) protects bones by inhibiting osteoclasts. Parathyroid Hormone (PTH, 84 amino acids) raises blood calcium. Melanocyte-Stimulating Hormones (alpha-MSH, 13 amino acids) regulate skin pigmentation and appetite — Melanotan II and PT-141 are analogs. Substance P (11 amino acids) transmits pain signals. And the mitochondrial-derived peptides — Humanin (24 amino acids) and MOTS-c (16 amino acids) — represent a recently discovered class encoded in mitochondrial rather than nuclear DNA.

Why This Matters for Research

Every research peptide connects back to this list. When you use CJC-1295, you're stimulating GHRH receptor signaling. When you use BPC-157, you're supplementing a gastric peptide. When you use semaglutide, you're activating GLP-1 receptor pathways. Understanding the natural peptide hormone system gives context to every research compound — what it mimics, what it modulates, and why it works the way it does.