So what actually is a peptide?
Your body is running thousands of tiny chemical messages right now. One just told your stomach to start digesting. Another nudged a blood vessel to relax. Several are quietly regulating your sleep cycle. Most of those messages are peptides.
A peptide is a short chain of amino acids, the same building blocks that make up proteins. Those amino acids are linked end-to-end by a chemical connection called a peptide bond, forming a chain anywhere from two to around fifty units long.
Think of amino acids like letters. A peptide is a short word: specific, readable, purposeful. A protein is a novel.
How short is 'short'?
Peptides vs. proteins: what's the difference?
Both are amino acid chains. The length changes what they can do.
Proteins are long enough to fold into complex 3D shapes: enzymes, structural scaffolds, antibodies. That architecture is what makes them useful as molecular machines. Peptides are too short to do that. Instead, they stay relatively flexible and mobile, which makes them excellent at one specific job: carrying a signal to the right receptor and triggering a response.
A useful analogy: if a protein is a Swiss Army knife, a peptide is a house key. Less versatile, but it fits one lock precisely and does exactly what it is supposed to.
How do they actually do anything?
Almost every peptide works the same way at a high level: it finds a matching receptor on a cell's surface, binds to it, and triggers something downstream. That "something" might be a change in gene expression, the release of another hormone, an immune response, or a shift in how the cell behaves.
The binding is highly specific. A peptide's shape and charge distribution determines exactly which receptor it fits. Change even one amino acid in the sequence, and the whole interaction can change. The peptide might bind more weakly, not at all, or to a completely different target. That precision is exactly what makes synthetic peptides so useful in research: you can dial in specificity in ways that small molecules often cannot match.
Why this matters for research
Researchers tend to think about peptides in three buckets, though the lines blur constantly.
The biggest bucket is signaling. Hormones like insulin and glucagon are peptides. They travel through the bloodstream and tell distant cells to take up glucose or release it.Neuropeptides like endorphins do the same in the nervous system. Most peptide research sits in this space because understanding how these signals work, and what happens when you amplify, block, or mimic them, has direct implications for metabolic disease, pain, and inflammation.
Some peptides are less about signaling and more about physical structure. BPC-157 is the most studied example. It is a 15-amino-acid fragment derived from a protein found in gastric juice, and it is studied in tissue repair models because of how it interacts with growth factor signaling. It does not repair tissue directly. It talks to the cells that do.
Then there are antimicrobial peptides, which are one of the oldest immune tools in biology. They show up in everything from frogs to humans and most work by physically disrupting bacterial membranes. Because they attack the membrane itself rather than a specific bacterial protein, bacteria find them harder to develop resistance against.
Lab results are not clinical results
How are research peptides made?
The dominant method is called solid-phase peptide synthesis, or SPPS. The process builds the sequence one amino acid at a time, each step chemically controlled so the chain grows in exactly the right order. Once assembled, the peptide is cleaved and purified by HPLC, a chromatography process that physically separates your target molecule from everything else the synthesis produced. Mass spectrometry then confirms the final product matches the intended sequence.
Where quality varies is in that purification step. A well-run synthesis with rigorous HPLC can reach 99%+ purity. A cheaper process that skips steps or cuts corners produces something that looks like your peptide on a label but behaves differently in an experiment.
The question we get asked most
Why purity matters more than you'd think
When you order a research peptide, the purity percentage is not just a quality signal. It tells you how much of what is in the vial is actually the compound you want. A peptide listed at 95% purity means up to 5% of the contents are something else: truncated sequences, leftover protecting groups, racemized residues, or synthesis byproducts.
That 5% can matter a lot. In a cell-based assay, impurities can trigger off-target responses that look like your peptide working when it is not. The research benchmark is 99%+ purity by HPLC, backed by a Certificate of Analysis (CoA) that shows the actual chromatography trace and mass spectrum for that specific batch.
If a supplier cannot show you a CoA, that is your answer.