What is a peptide? | Living+ Peptides

A peptide is a short chain of amino acids. The National Human Genome Research Institute says a peptide typically has 2 to 50 amino acids, joined by chemical links called peptide bonds ^[1]. Longer chains build proteins ^[1]. Your body makes many peptides, and some medicines are peptides too ^{[5, 6]}.

Amino acids are the building blocks

Amino acids are small molecules that join to form proteins ^[2]. There are 20 types of amino acids that can be combined to make a protein ^[3]. The body can make some of them. Nine are called essential, because the body cannot make them and they must come from food ^[2].

The body uses amino acids to make proteins. MedlinePlus says these proteins help the body break down food, grow, repair tissue and carry out many other jobs ^[2]. Nonessential amino acids are ones the body can make even if they are not in the food you eat ^[2].

The order of amino acids in a chain matters. The National Library of Medicine says the sequence of amino acids sets each protein's 3-D shape and its job ^[3]. The same idea applies to peptides. Small changes can matter. The Ozempic label says semaglutide is modified at position 8 to protect it from breakdown by an enzyme called DPP-4 ^[5].

Peptides vs proteins

Size is the main difference. The genome institute describes peptides as roughly 2 to 50 amino acids. Chains of 51 or more are called polypeptides, and proteins are made from one or more polypeptides ^[1]. Proteins can hold hundreds or thousands of amino acids ^[3].

The FDA uses its own cutoff for legal purposes. It treats a chain of 40 or fewer amino acids as a "peptide" and a longer chain as a protein ^[4]. This line has real effects. Since March 23, 2020, many protein drugs, such as insulin and human growth hormone, are regulated as biological products, while peptides of 40 or fewer amino acids were not affected by that change ^[4].

Peptide (FDA): 40 or fewer amino acids ^[4].
Protein (FDA): more than 40 amino acids ^[4].
Peptide (general science use): about 2 to 50 amino acids ^[1].

Natural peptides in the body

Many hormones are peptides. Oxytocin is one. The Pitocin label calls it a nonapeptide, a chain of nine amino acids, found in extracts of the pituitary gland of mammals ^[6]. Human GLP-1 is another natural peptide. The drug semaglutide is built on it ^[5].

Peptide drugs

A peptide drug is a peptide made to be used as a medicine. Some are close copies of natural peptides. The Pitocin label says its oxytocin is made synthetically to avoid contamination with vasopressin, a related hormone ^[6]. Others are changed on purpose. Semaglutide is a GLP-1 analog that shares 94% of its sequence with human GLP-1, and its backbone is produced by yeast fermentation ^[5].

FDA-approved peptide drugs have labels that list their uses, doses and side effects ^{[5, 6]}. You can read about two of them on this site: semaglutide and oxytocin.

Unapproved peptides

Many peptides discussed online have no FDA approval. FDA keeps a list of bulk drug substances that may present significant safety risks in compounding. Several peptides appear on it, including GHRP-2, GHRP-6 and kisspeptin-10 ^[7]. For BPC-157, FDA says it has no, or only limited, safety information for the proposed routes ^[7].

Compounded drugs, including compounded peptides, are not FDA-approved. FDA does not check their safety, effectiveness or quality before they are sold ^[8]. You can see the status of each peptide on the FDA Peptide Status Tracker.

Where to go next

If you want to know how peptide drugs reach patients, read how peptides are prescribed in the US ^[8]. For risks, see peptide safety basics ^[7]. To judge research claims, see how to read a peptide study ^[1].

Frequently asked questions

How many amino acids are in a peptide?

The National Human Genome Research Institute says a peptide is typically 2 to 50 amino acids ^[1]. For legal purposes, FDA treats 40 or fewer amino acids as a peptide ^[4].

What is the difference between a peptide and a protein?

Length. Peptides are short chains, and proteins are made of one or more longer chains that can have hundreds or thousands of amino acids ^{[1, 3]}.

Is insulin a peptide or a protein?

FDA regulates insulin as a protein product. Since March 23, 2020, insulin products are regulated as biological products ^[4].

Are peptides natural?

Many are. Oxytocin is a peptide hormone found in the pituitary gland of mammals, though the drug version is made synthetically ^[6].

Are all peptides FDA-approved drugs?

No. Some peptides are approved drugs with FDA labels, such as semaglutide ^[5]. Others are unapproved, and FDA lists several as possible safety risks in compounding ^[7].

Are compounded peptides FDA-approved?

No. FDA says compounded drugs are not FDA-approved, and it does not check their safety, effectiveness or quality before they are sold ^[8].