Educational reference · not medical advice
Short chains of amino acids run an enormous amount of the body's signalling — appetite, healing, sleep, immune response. This is a plain-language guide to what they are, how they act, and how strong the evidence for each one really is.
01 — Foundations
Proteins are long chains of amino acids. Cut that chain short — conventionally to fewer than about fifty links — and you have a peptide. The length matters less than the sequence: the order of the amino acids determines the shape, and the shape determines what the molecule can bind to.
The body uses peptides as messengers. Insulin, glucagon, GLP-1, growth hormone and dozens of immune signals are all peptides. They are made on demand, released into the blood, act on a target cell, and are then dismantled by enzymes within minutes. That fast on-off cycle is the point: it lets the body adjust second by second.
Peptide medicines copy that logic. Some are identical to a natural hormone, some are modified to last longer, and some are fragments of a larger protein whose full behaviour in humans has never been established. Which of those three you are looking at changes how much weight the evidence deserves.
02 — Signalling
Three ideas explain almost everything about how these molecules behave — and why an injected peptide and an oral capsule are not the same thing at all.
A peptide works by fitting a receptor — a protein on or inside a cell that recognises one specific shape. Binding switches a signal on inside the cell, and the cell responds. Most peptide drugs are agonists: they imitate the body's own messenger at that receptor.
One peptide, several receptors, is why side effects often appear in unrelated systems.
Half-life is how long it takes for half a dose to leave the blood. Natural peptides are broken down in minutes. Medicines are engineered to resist that — semaglutide binds albumin to stretch its half-life to about a week, which is why it is injected weekly rather than hourly.
Short half-life means frequent dosing. Long half-life means less control if a dose goes wrong.
Stomach acid and digestive enzymes dismantle peptides, so almost none survive being swallowed. That is why most are injected into the fat under the skin, where absorption is slow and predictable. Oral forms exist only where the molecule has been specially engineered to survive.
The route changes the dose, the speed and the side effects. They are not interchangeable.
Why oral usually fails: the gut is built to break peptides into single amino acids before they reach the blood. Only molecules with a deliberate chemical workaround — or very small ones — survive it.
03 — Most popular
The peptides people ask about most often, with the characteristics that matter: what field they sit in, what they have actually been studied for, how strong the human evidence is, and whether a regulator has approved them.
Healing & repair
A synthetic fragment of a gastric protein, widely promoted online for injury recovery. Human trial evidence is very thin; almost all data comes from animal studies.
Studied for
Reproductive & hormonal
The melanocortin peptide approved as Vyleesi for low sexual desire in premenopausal women — an on-demand drug, not a tanning product.
Studied for
Cosmetic & dermatologic
A copper-binding tripeptide found naturally in human plasma and skin, used in cosmetic formulations for skin remodelling and studied for wound healing.
Studied for
Mitochondrial & antioxidant
A mitochondrial-derived peptide studied for metabolic control; the biology is new and human trials are tiny.
Studied for
GLP-1 & incretin
An investigational triple agonist acting on GIP, GLP-1 and glucagon receptors, with the largest weight loss reported for any peptide in an early trial. Not approved and not available outside studies.
Studied for
Healing & repair
A synthetic fragment of thymosin beta-4, studied in animals for wound healing and cell migration. No approved status and no robust human trials.
Studied for
Two labels appear on every entry, and they answer different questions.