What are peptides? Hormones, medicines, research vials and nootropics

01The short version

A peptide is a short chain of amino acids, the same building blocks as protein, just fewer of them. Two to about fifty amino acids is a peptide; longer than that is a protein. Your body makes thousands of them (insulin, oxytocin, and most hormones are peptides), and laboratories make more. In the UK the word now covers everything from collagen powder to prescription weight-loss injections to nootropic nasal sprays, which is why it confuses people.

02What a peptide is, chemically

Amino acids link together through peptide bonds into chains. A chain of two is a dipeptide, three a tripeptide, and so on. Semax is seven amino acids; insulin is 51; a typical protein is hundreds. The sequence determines the shape and the shape determines what the molecule does, which is why a seven-amino-acid chain can have a precise effect on a specific receptor while a random chain does nothing.

Because they are made of amino acids, peptides are broken down by digestion into amino acids. That single fact explains most of what follows: why they are injected or sprayed rather than swallowed, why they do not accumulate, and why "oral peptide" products are usually either digested before they work or are not really peptides.

03The kinds of peptides people mean

Hormones and signalling peptides your body makes

Insulin, glucagon, oxytocin, vasopressin, GLP-1, growth hormone releasing hormone, endorphins. Medicine has used these for a century; insulin was the first, in 1922.

Licensed peptide medicines

Semaglutide (Ozempic, Wegovy) and tirzepatide (Mounjaro) are GLP-1 peptides licensed in the UK for diabetes and weight management, on prescription. Desmopressin is a peptide nasal spray for bed-wetting. These are medicines with a licence, a prescriber and a pharmacy behind them.

Research peptides

Compounds with animal data and little or no human licensing, sold as "research chemicals": BPC-157, TB-500, ipamorelin, CJC-1295, GHK-Cu, epitalon and dozens more. Legal to possess in the UK, not licensed, not tested by anyone unless the seller does it. Research peptides in the UK.

Nootropic peptides

Semax and Selank, developed in Russia and taken as nasal sprays for attention and stress respectively. Decades of use, a small human literature, and the only category COGENT makes. The Semax guide.

Cosmetic and food peptides

Collagen peptides in powders and "peptide serums" in skincare. Different world: hydrolysed protein fragments taken as food, or topical signalling peptides at cosmetic doses. Legal, widely sold, and mostly modest in effect.

04What peptides do

Whatever their sequence tells a receptor to do. GLP-1 peptides tell the pancreas to release insulin and the brain that you are full. Semax raises BDNF and modulates dopamine and serotonin [2][3][4]. BPC-157 in animals speeds tissue repair. GHK-Cu in skin cells stimulates collagen. There is no general "peptide effect"; there are hundreds of specific ones, some proven in people, most proven only in rats, some not proven at all.

05Are peptides safe, and are they legal?

Both questions have the same answer: it depends entirely on which peptide, from where, at what dose. A licensed medicine from a pharmacy is as safe as its trials say. A research vial from an anonymous website is as safe as whatever is actually in it. Our guides: Are peptides legal in the UK? and Are peptides safe?.

06How peptides are taken

Injection under the skin (most research peptides and the GLP-1s), nasal spray (Semax, Selank, desmopressin, oxytocin), and by mouth for the few designed to survive it. The reasons are in oral, nasal or injectable. Anyone reconstituting a vial needs the peptide calculator and the reconstitution guide.