What are peptides?

Peptides are short chains of amino acids, the same building blocks that make up proteins, usually 2 to 50 of them linked together (NHGRI). Your body uses peptides as signals, and some of the most widely used medicines are peptides, including insulin and GLP-1 drugs such as semaglutide and tirzepatide. Many other peptides sold online are not approved for human use and have little or no human research behind them.

Peptides vs proteins: what’s the difference?

Amino acids join end to end through chemical links called peptide bonds. A short chain, typically 2 to 50 amino acids, is a peptide. A longer chain, 51 or more, is a polypeptide, and proteins are built from one or more polypeptides folded into a shape (NHGRI). So peptides and proteins are made of the same material; the difference is mostly length.

Peptides can be natural (made by your body), modified versions of natural ones, or entirely lab-designed sequences. Their names often hint at where they came from: GLP-1 is “glucagon-like peptide-1”, a gut hormone, while code names such as BPC-157 or TB-500 usually mean a lab-made fragment that was never developed into a medicine.

What do peptides do in the body?

Many peptides work as messengers. They travel in the blood or between nearby cells and bind to receptors, proteins on the cell surface that switch a response on or off. Insulin, which lowers blood sugar, is a peptide hormone. So is GLP-1: released by cells in the gut after a meal, it increases insulin, lowers glucagon, slows how fast the stomach empties and reduces food intake (Drucker, 2018).

Natural peptides are usually short-lived. Native GLP-1 lasts only 1.5 to 2 minutes in the blood because enzymes break it down quickly (Saxenda label). That is why peptide medicines are often engineered versions of a natural signal: liraglutide, for example, is GLP-1 with one amino acid changed and a fatty acid attached, so it resists those enzymes and lasts hours instead of minutes.

What are peptides used for in medicine?

Since insulin was introduced almost a century ago, more than 80 peptide drugs have reached the market, for conditions including diabetes, cancer, osteoporosis, multiple sclerosis, HIV infection and chronic pain (Muttenthaler et al., 2021). These went through the full drug-approval process: controlled trials, FDA review of the data and manufacturing, and an official label that sets out what the medicine is for and its risks.

Some approved peptide medicines you may have heard of:

Sources: the Wegovy, Zepbound, Saxenda and Egrifta WR prescribing information.

Each is approved only for the uses on its label. Tesamorelin, for example, is approved to reduce abdominal fat in adults with HIV and lipodystrophy, and its label states it “is not indicated for weight loss management” (Egrifta WR label). Our compound pages give the US status of each peptide we cover.

Can peptides be taken as pills?

Usually not well. Peptides taken by mouth are poorly absorbed through the gut wall and broken down by digestive enzymes (Buckley et al., 2018). The oral semaglutide tablet works because it is made with an absorption enhancer (SNAC) that protects it in the stomach; the researchers found the effect is specific to that compound and formulation.

Not every GLP-1 pill is a peptide. Orforglipron, approved in 2026 as Foundayo, is a small-molecule, “nonpeptide” drug that acts on the same receptor (Wharton et al., 2025; Foundayo label).

Capsules and powders sold as “peptide supplements”, such as collagen peptides, are a different category again. The FDA does not approve dietary supplements before they are sold (FDA). We cover what collagen studies found on peptides for skin.

What does “research use only” mean?

Many peptides are sold online as powders labeled “research use only” or “not for human consumption”. The FDA has repeatedly said that such labels do not change what a product is: when a website’s own claims show a product is meant for people, the FDA treats it as an unapproved new drug (FDA warning letter, 2026). For GLP-1 look-alikes sold this way, the FDA says they are “of unknown quality and may be harmful” (FDA).

The FDA is particularly concerned about injectables, which “bypass some of the body’s key defenses against toxins and microorganisms” (same warning letter). Peptinote never links to, names or ranks sellers.

How are peptides regulated in the US?

A peptide can reach people by several routes, and each means something different:

• FDA-approved drug. Reviewed for safety, effectiveness and quality, with an official label. Examples: Wegovy, Zepbound, Saxenda.
• Compounded drug. Made by a pharmacy for an individual patient with a prescription. Compounded drugs are not FDA-approved, and pharmacies may use only certain bulk ingredients (FDA). The FDA has flagged many peptides as possible safety risks in compounding (FDA).
• Cosmetic. Creams and serums don’t need FDA approval, but a product whose intended use is to change how the body works is a drug under the law (FDA).
• Unapproved drug. Anything else sold for use in people, including most “research” peptides.

The peptide regulation tracker shows the current status of every compound we cover, with a dated timeline of FDA actions.

Are peptides safe?

There is no single answer, because “peptides” covers everything from insulin to untested lab fragments.

Approved peptide medicines have known, labeled risks. GLP-1 drugs, for example, carry a boxed warning about thyroid C-cell tumors seen in rodents, and must not be used by people with a personal or family history of medullary thyroid carcinoma (Zepbound label). Your prescriber weighs those risks with you.

Unapproved peptides mostly have unknown risks. For many, the FDA says it has no or limited safety information and “lacks sufficient information to know whether the drug would cause harm when administered to humans”. It also warns that injected peptides may provoke immune reactions because of aggregation and peptide-related impurities (FDA). Athletes face another risk: many peptides are banned in sport (WADA).

How to read peptide research

Claims online often rest on early research. Before you trust one, ask four questions:

1. In whom? Cells and animals come first, and most treatments stop there. An analysis of 367 therapies tested in animals found about half reached any human study and only 5% reached regulatory approval (Ineichen et al., 2024).
2. How many people, and compared with what? A small study with no comparison group can’t separate an effect from chance, placebo or natural recovery. Randomized, placebo-controlled trials can.
3. Measuring what? A change in a blood marker is not the same as people feeling or doing better.
4. Who reviewed it? FDA approval means an independent review of all the data and of how the product is made.

Every compound page on Peptinote carries an evidence grade, from “animal or lab studies only” to “strong human evidence”. Our editorial policy explains how we grade.

Peptides by topic

Most people search for peptides with a goal in mind. Each guide below sets out what is approved, what is marketed, and what the research actually shows.

• Weight lossApproved GLP-1 medicines, drugs in trials, and peptides sold for fat loss.
• Muscle growthGrowth hormone peptides, what trials show, and anti-doping rules.
• SkinPeptide creams, GHK-Cu, collagen supplements and injections.
• Injury recoveryBPC-157, TB-500 and the gap between animal and human evidence.
• Regulation trackerThe US status of every compound, with a dated timeline of FDA actions.

Questions people ask