Peptides are short chains of amino acids joined by a peptide bond, usually 2 to 50 amino acids, which is far shorter than a protein. Because of that they cross cell membranes more easily than large proteins and act mainly as signalling molecules: they pass specific instructions to cells, for example “increase collagen production” or “release growth hormone”.
What is a peptide?
A peptide is a chemical compound built from amino acids joined by a peptide bond, the same type of bond that links amino acids in proteins. The difference lies in the length of the chain: peptides usually have 2 to 50 amino acids, proteins 50 and more, often several hundred. A shorter chain means a simpler spatial structure, since peptides rarely fold into complicated three-dimensional forms the way proteins do, and a smaller molecular mass, which makes it easier for them to enter cells and bind to receptors on their surface.
Peptides occur naturally in the body. Insulin, glucagon and oxytocin are peptide hormones, and antimicrobial peptides such as defensins are part of innate immunity. The peptides used in cosmetics and supplements are usually synthetic: a laboratory reproduces or modifies a sequence known from natural peptides in order to strengthen a particular effect.
How do peptides differ from proteins?
Mainly in the length of the chain and in function: peptides act above all as signals, while proteins do the physical work of the body. They are enzymes, structural elements such as collagen and keratin, or transporters such as haemoglobin. A full comparison of the structure and function of both groups, with examples from each, is in a separate article on peptides versus proteins.
How do peptides work in the body?
A peptide binds to a receptor on the surface of a cell, much as a key enters a lock, and that contact triggers a specific reaction inside the cell: production of a protein, release of a hormone, migration of the cell towards a site of damage. The peptide itself does not enter the interior of the cell and does not change its DNA. It works as a carrier of information, not as building material.
What effect a given peptide produces depends on which receptor it fits. That is why three peptides of similar size can do entirely different things: one stimulates tissue healing, the second affects appetite, the third affects skin pigmentation.
What are the main types of peptides?
Three groups come up again and again in this shop, because the range and the articles are built around them:
- Recovery peptides, studied for the healing of tendons, ligaments and the gastric mucosa, such as BPC-157 and TB-500. The mechanism and the state of research are in the article on recovery peptides. The products are in the recovery peptides category.
- Peptides that act on growth hormone, GHRH analogues and ghrelin mimetics (GHRP), which stimulate the pituitary to release the body’s own growth hormone. The mechanism is explained in the article on growth hormone peptides. In the shop they correspond to the growth hormone peptides category.
- Metabolic peptides (GLP-1), semaglutide, tirzepatide and retatrutide, which affect appetite and glucose metabolism. An overview is in the article on GLP-1 and incretins. These molecules are collected in the weight loss peptides category.
A separate category, outside those three, are the cosmetic peptides used in skincare, that is signal, neurotransmitter, carrier and enzyme-inhibitor peptides. They are described in a separate article on peptides in skincare.
Is using peptides legal and safe?
It depends which peptide you mean and what you want to use it for. Some, such as semaglutide and tesamorelin, have the status of a medicine in some countries; some appear on the list of substances prohibited in sport; and most of those you can buy labelled “for research” have no status as a medicine and have not been assessed for safety in humans in controlled clinical trials. The details are in the article on the legal status of peptides.
Where to start: what to look at when choosing a peptide
Before you buy a peptide, check three things: whether the seller provides a certificate of analysis giving purity and the actual content of the substance; how it has to be stored after reconstitution, since most require a fridge and lose activity at room temperature; and which of the categories above it belongs to, because that decides what can realistically be expected of it. More is in the articles on how to spot a counterfeit peptide and how to store peptides.
Frequently asked questions
How do peptides differ from proteins?
In the length of the amino acid chain, 2 to 50 for peptides and 50 or more for proteins, and in function: peptides act mainly as signals, proteins as enzymes, structural elements and transporters.
Are peptides steroids?
No. Anabolic steroids are derivatives of testosterone and act on androgen receptors. Peptides have a different chemical structure, a chain of amino acids, and a different mechanism of action: they usually bind to signalling receptors rather than steroid hormone receptors.
Are peptides sold “for research” safe for humans?
There is no guarantee of that. Research-use status usually means the manufacturer has not run or not completed clinical trials in humans, and the long-term safety of many of these substances is not described in controlled studies.
Where should a beginner start?
With understanding which category the peptide you are interested in belongs to, whether recovery, hormonal, metabolic or cosmetic. Each has a different mechanism and a different level of scientific evidence, described in separate articles here.