Peptides are short chains of amino acids, the building blocks of proteins. Your body makes thousands of them, and they act as messengers that switch processes on and off, from blood sugar control to healing. Some peptides are approved medicines, some are used in skin care, and many sold online are research chemicals that are not approved for people.
What are peptides made of?
Peptides are made of amino acids linked in a chain. A chain of 2 to about 50 amino acids is usually called a peptide; longer chains fold into proteins.
Think of amino acids as single building blocks. Stack a few together and you have a peptide; build a large, folded structure and you have a protein such as collagen.
What do peptides do in the body?
Many peptides are hormones or signals that tell cells what to do. Insulin is a peptide that lowers blood sugar, and others help control appetite, digestion, blood pressure, sleep and healing.
Because they are natural signals, scientists study peptides as possible medicines. A peptide can be copied in a lab, or changed slightly so it lasts longer in the body.
What is peptide therapy?
Peptide therapy means using peptides as treatments, usually given by injection. It covers two very different groups:
- Approved medicines, such as insulin, semaglutide and tirzepatide for weight loss, and some hormone medicines. These have passed large clinical trials and are prescribed by doctors.
- Research peptides, sold by some clinics and online sellers. Most have been studied mainly in animals, are not approved for human use and are not checked for purity.
The wellness term “peptide therapy” usually means the second group. In 2026 the FDA changed how it treats several of these peptides for pharmacy compounding, but none of them became approved medicines (see are peptides legal?).
What is a peptide serum?
A peptide serum is a skin care product with peptides added, usually to help skin look firmer or smoother. The best-known is the copper peptide GHK-Cu.
The evidence is modest. Small studies show some peptide creams improve fine lines and firmness over about three months, but many peptides have trouble getting through the outer layer of skin, and results differ a lot between products; see peptides for skin.
Approved medicines vs research peptides
The biggest difference is evidence. An approved medicine has been tested in large trials in people, made to strict quality standards and labeled with its uses and risks. A research peptide has none of that, even if it has an impressive name or a long list of claimed benefits.
The guides below say clearly which kind each one is. Several research peptides are also banned in sport by the World Anti-Doping Agency.
Are peptides safe?
Approved peptide medicines are as safe as their labels and doctors say, which still includes real side effects. For research peptides, nobody knows: there are few or no human studies, and products bought online may be mislabeled or contaminated.
See peptide side effects for the common reactions and risks by type. If you are thinking about using any peptide, talk with a qualified healthcare professional first.
How do you mix and measure peptides?
Most injectable peptides come as a powder that is mixed with bacteriostatic water. The peptide calculator turns your vial size, the water you add and your dose into syringe units, and the guide on how to reconstitute peptides walks through the steps.