What Are Peptides? Natural and Synthetic Peptides, and How They Differ From Proteins

What is a peptide?

A peptide is a short chain of amino acids joined by chemical links called peptide bonds. The U.S. National Human Genome Research Institute gives a typical size of 2 to 50 amino acids. [1] Amino acids are the small building blocks the body uses to make proteins, and there are 20 kinds that make up proteins. [2]

That size range is a convention, not a law of nature. The U.S. FDA uses a different line for its own purposes, and the question of where peptides end and proteins begin is covered on its own page: peptides vs proteins.

Where peptides come from

Peptides can be isolated from animal tissue, produced synthetically in a laboratory, or made through recombinant expression, which means living cells such as bacteria are engineered to produce them. [3] Examples of each appear in approved medicines. Ziconotide is a peptide derived from a cone snail, teduglutide is made in modified E. coli bacteria, and liraglutide is chemically synthesized. [4]

Many peptides also occur in the human body and often act as signaling molecules. [3] More on that in endogenous vs administered peptides.

What peptides do

Peptides serve many roles. Reviews describe therapeutic peptides as acting like hormones, growth factors, neurotransmitters, ion channel ligands or anti-infective agents. [4] Most of them work by binding to receptors on the outside of a cell. [4] The plain-language version is on the receptors and cell signaling page.

A useful sign of how established the field is: a 2018 review counted over 60 peptide drugs approved in the United States and other major markets, with more than 150 peptides in active development at that time. [5] The same review notes that peptide therapeutics have played a notable role in medical practice since insulin therapy began in the 1920s. [5]

One word, many different things

"Peptide" on a label can describe very different products, and they are regulated differently:

• Approved prescription medicines, such as insulin or GLP-1 drugs. See GLP-1 medicines.
• Cosmetic ingredients. In the U.S., cosmetic products and ingredients, other than color additives, do not need FDA approval before they go on the market. [6] See skin and cosmetic peptides.
• Food-derived peptides, such as collagen peptides, covered in collagen and dietary peptides.
• Research compounds and compounded products sold outside the approval system, where evidence in people is often thin. See BPC-157 for an example.

Three terms are easy to mix up: the molecule (what it is), the brand (what it is sold as) and the formulation (how it is made up into a product). They are related but not interchangeable. "Peptide" is also not the same word as "supplement," and not every injectable is a peptide.

A note on evidence labels

Across this library we use plain labels: approved medicine, established, promising but limited, mixed, insufficient evidence, preclinical (cells or animals only), no good evidence of benefit, evidence of harm, and marketing claim. This page is background science, so it mostly describes how things are defined, not whether any product works. There is no shared set of benefits or risks across "peptides"; each compound has to be judged on its own evidence.