What Are Peptides? What They Do in the Body, and Which Are Actual Drugs

Peptides are short chains of amino acids, typically 2 to 50, joined by chemical links called peptide bonds.^[1] Your body makes them as hormones and signals; insulin and oxytocin are the classic examples.^[5] More than 80 had reached the market as drugs by 2021,^[6] and semaglutide, the drug inside Ozempic and Wegovy, is one of the best known.^[9] The word covers very different things, though. Many peptides sold online have no FDA approval for any use, and being a peptide says nothing about whether a product works or is safe.^[17][18]

What are peptides, in simple terms?

Think of amino acids as beads. There are 20 standard kinds, and the body can make some of them while others must come from food.^[2] String a few beads together and you have a peptide. String hundreds or thousands together and fold the result, and you have a protein.^[3] The order of the beads decides what the chain does, which is why two peptides of similar length can have nothing in common.

The boundary is a convention. The National Human Genome Research Institute puts it at about 50 amino acids.^[1] US drug regulation uses 40: any defined chain longer than that counts as a protein.^[4] So insulin, with 51 amino acids, is often called a peptide by scientists^[5] and sits on the protein side of FDA’s line. Tesamorelin, at 44,^[11] was moved to a biologics license for the same reason.^[20] The chemistry of the GLP-1 drugs is laid out in are GLP-1 drugs peptides?

What do peptides do in the body?

Mostly, they carry messages. Natural peptides act as hormones, growth factors and neurotransmitters, and some defend against infection.^[5] A peptide usually works by fitting a receptor on the outside of a cell and switching it on or off, since peptides generally cannot cross the cell membrane.^[5] A few familiar examples:

• Oxytocin, nine amino acids, is released from the pituitary and is given by injection in hospitals during labor.^[7]
• Insulin regulates blood glucose.^[5]
• GLP-1 is a gut hormone that affects blood sugar and body weight. The natural version lasts only minutes in the blood.^[8]
• Growth hormone-releasing hormone is made in the hypothalamus and tells the pituitary to release growth hormone.^[11]
• Glutathione, three amino acids, is a central antioxidant in cells.^[15]

Peptides also come from food. Proteins contain shorter active sequences that can be released during digestion or processing.^[14] Researchers have identified many in the lab, but a review of the field points to poor survival in the gut, variable absorption and a lack of well-designed clinical trials as the obstacles to health claims.^[14]

What are the main types of peptides?

Scientists sort peptides by origin and function. For anyone reading a label or a clinic menu, the more useful split is by what kind of product it is, because that decides who checked it and what evidence exists.

Which peptides are actual drugs?

Plenty. By a 2021 count, more than 80 peptide drugs had reached the market for diabetes, cancer, osteoporosis, multiple sclerosis, HIV infection and chronic pain.^[6] Early ones copied human hormones. Newer ones change the sequence so the drug lasts longer or binds better.

An approval covers the use that was tested, nothing more. Tesamorelin is a good example: its label limits it to one kind of abdominal fat in adults with HIV.^[11] The fuller list, with each label, is in FDA-approved peptides.

Why are most peptide drugs injected?

Two weaknesses explain it. Peptides are unstable in the body and cross membranes poorly,^[5] and a swallowed peptide faces the same digestion as any other protein in a meal.^[14] Natural GLP-1 shows how short-lived these molecules can be: its half-life is about 1.5 minutes after an IV dose.^[8] Drug makers changed the chain and added a fatty side group so that semaglutide lasts about a week.^[9]

Getting one through the gut takes real engineering. Semaglutide tablets contain an absorption enhancer called SNAC and have to be swallowed fasting with a little water, and even then only about 0.4% to 1% of a Rybelsus dose reaches the blood.^[9] This is why a claim that a peptide works as a capsule or a spray needs its own evidence.

Are all peptides sold today approved or tested?

No, and this is where the word causes the most confusion. Popular names such as BPC-157, TB-500, MOTS-c and Epitalon are not components of any FDA-approved drug,^[17] and most have little human data. Our count of which peptides on the menu have human trials shows how uneven the record is. A 2026 sports-medicine review describes a gray market operating largely outside regulatory oversight, where rigorous human safety data are scarce.^[19] On BPC-157, FDA says the agency lacks the information to know whether it would cause harm in people.^[18]

On October 28, 2026, HHS said it does not intend to take enforcement action against 503A pharmacies that compound six peptides (BPC-157, TB-500, Epitalon, Semax, KPV and MOTS-c) when strict conditions are met.^[17] That is an interim enforcement position, and the Federal Register notice of October 30 calls it a draft, with two weeks for written comments.^[21] The policy itself says compounded drugs are not FDA-approved, and it gives research-use-only products as the risk it wants to discourage.^[17] For specifics, see are peptides safe? and are peptides legal?, or look up any name in the peptide status checker.

One more mix-up comes from gyms: peptides are not steroids. They differ in chemistry and in US law. And NAD+, often sold beside them, is not a peptide at all, because it is built from nucleotides.