Glossary, mechanisms, and fundamental concepts.
Peptides are short chains of amino acids that act as your body's signaling system. This guide explains what they are, how they work, their medical uses from GLP-1 drugs to skincare, and where the science stands.
Native GLP-1 lasts about 2 minutes in the bloodstream. Oxytocin: 3-5 minutes. Ghrelin: roughly 30 minutes. Most unmodified peptides are eliminated from the body in a matter of minutes, not hours.
Every peptide you have ever read about -- from [BPC-157](/peptides/bpc-157-complete-scientific-guide/) to [semaglutide](/peptides/semaglutide-complete-pharmacology-guide/) -- is fighting a losing battle against chemistry.
Cells have a problem. They need to get the right proteins to the right places --- exporting some outside the cell, embedding others in the membrane, and keeping the rest in the cytoplasm.
Can you be allergic to a peptide? The short answer is yes -- but the details matter more than the headline.
Every protein you eat is a chain of amino acids held together by peptide bonds. When you digest a steak, a scoop of whey, or a bowl of lentils, your body's job is to break those bonds -- systematically, efficiently, and completely enough to absorb the amino acids inside.
You are already eating peptides. Every glass of milk, every piece of grilled salmon, every bowl of fermented yogurt contains peptide fragments with measurable biological activity -- lowering blood pressure, scavenging free radicals, killing bacteria, or modulating your immune system.
Every drug falls somewhere on a molecular spectrum. At one end, you have small molecules — compact chemical compounds like aspirin, metformin, and atorvastatin that have dominated pharmacy shelves for over a century.
The history of peptide therapeutics is a 100-year story of scientific breakthroughs, Nobel Prizes, and paradigm shifts in medicine.
Peptide science has its own language. Open any research paper, skim a compounding pharmacy catalog, or browse a clinical trial listing, and you'll run into a wall of abbreviations — GHRP, SPPS, DPP-4, SC, Fmoc. This guide decodes them all.
Whether you're a graduate student running a literature search, a clinician checking the evidence behind a peptide therapy, or a curious reader trying to verify claims from a supplement company, knowing where to find reliable peptide data is half the battle.
Every surface of the human body that contacts the outside world — skin, lungs, gut, urinary tract — is guarded by a chemical defense system older than the adaptive immune system itself.
In 1931, Ulf von Euler and John Gaddum isolated something unusual from horse brain and intestine. The substance caused smooth muscle to contract and blood pressure to drop, but it was not any known neurotransmitter.
Open any peptide research paper and you will encounter strings like "Ac-D-Trp-Ala-Trp-D-Phe-Lys-NH2" or "GHRP-6" or "H-Gly-Arg-Gly-Asp-Ser-OH." For the uninitiated, this looks like a different language.
When a vial is labeled "BPC-157, 98% purity," what does that actually mean? Where did that number come from? And should you trust it?
A peptide can be brilliantly designed, perfectly synthesized, and biologically potent — but none of that matters if it disappears from the bloodstream in two minutes.
A native peptide injected into the bloodstream faces a hostile environment. Proteases cleave it within minutes. The kidneys filter anything under ~60 kDa into the urine. The gastrointestinal tract destroys what is swallowed.
Every therapeutic peptide --- from [semaglutide](/peptides/semaglutide-complete-pharmacology-guide/) to [BPC-157](/peptides/bpc-157-complete-scientific-guide/) to the insulin in a diabetic's pen --- starts as raw amino acids that must be assembled in the correct sequence.
Growth hormone (GH) secretion is not random. It follows a tightly orchestrated pattern --- pulsatile bursts primarily during deep sleep, regulated by a push-pull system of stimulatory and inhibitory signals from the hypothalamus, stomach, liver, and the pituitary gland itself.
Your brain runs your endocrine system through a relay station the size of an almond. The hypothalamus, sitting at the base of the brain, produces peptide hormones that travel a few millimeters through a specialized blood supply to reach the pituitary gland.
A peptide floating in your bloodstream is just a molecule. It becomes a biological signal the moment it locks onto a receptor — a specialized protein embedded in a cell's membrane that converts the peptide's presence into an intracellular response.
Peptide therapies are no longer a niche topic. Millions of people now take GLP-1 agonists like [semaglutide](/peptides/semaglutide-complete-pharmacology-guide/) and [tirzepatide](/peptides/tirzepatide-dual-gipglp-1-agonist-profile/) for diabetes and weight management.
Collagen is the most abundant protein in your body. It is the structural scaffolding of your skin, the shock absorber in your joints, the framework of your bones, and the glue that holds your tendons and ligaments together. Starting around age 25, you lose roughly 1% of your collagen per year.
Every peptide has a side effect profile. For FDA-approved peptide drugs, that profile is documented through clinical trials involving thousands of patients. For research peptides, the data is thinner — sometimes limited to animal studies, small pilot trials, or anecdotal reports.
Whether you're a clinician adjusting dosing schedules or a patient trying to understand why your medication requires daily versus weekly injections, half-life is the number that explains it all.
Peptide therapy has gone from niche biohacker territory to mainstream medicine in the span of a few years.
The FDA has approved roughly 100 peptide-based drugs since insulin first reached patients in 1922. That number continues to grow: peptides accounted for about 10% of all new FDA drug approvals between 2020 and 2024, and the peptide therapeutics market is projected to exceed $49 billion by 2026.
Your body runs on chemical signals. Among the most important are peptide hormones --- short chains of amino acids that act as molecular messengers, traveling through the bloodstream to tell distant organs what to do and when to do it.
How a peptide enters the body determines how much of it actually reaches its target. A peptide injected subcutaneously might deliver 60-90% of the dose into the bloodstream. The same peptide swallowed as a pill might deliver less than 1%.
Your body has a built-in system for controlling blood sugar after meals. At the center of that system sits the GLP-1 receptor, a molecular switch on the surface of pancreatic beta cells, brain neurons, and cells throughout the gut.
Your body runs on peptides. Right now, as you read this, hundreds of distinct peptide molecules are circulating through your bloodstream, firing across synapses in your brain, patrolling your skin for bacteria, and shuttling signals between your mitochondria and your cell nuclei.
Ask a room of biochemists where peptides end and proteins begin, and you will get slightly different answers from each one. The two molecules are built from the same building blocks — amino acids linked by peptide bonds — yet they behave in fundamentally different ways.
Not all peptides are created equal. Some are just two amino acids long and small enough to slip through your intestinal wall intact. Others stretch to 50 residues and blur the line with full-sized proteins.
Every peptide drug, every collagen supplement, every antimicrobial defense molecule in your immune system comes down to the same building blocks: amino acids linked by peptide bonds. These are the atomic-level fundamentals.
You know that peptides are short chains of amino acids. You may know that [semaglutide](/peptides/semaglutide-complete-pharmacology-guide/) helps with weight loss and [BPC-157](/peptides/bpc-157-complete-scientific-guide/) is studied for tissue repair.
Peptide science comes with its own language. Between the biochemistry, the pharmacology, the drug names, and the abbreviations, it's easy to get lost in terminology before you even reach the actual science.