PeptideJournal
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What Are Peptides? The Complete Beginner's Guide

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.

If you've picked up a newspaper, scrolled social media, or talked to your doctor in the past three years, you've heard about peptides. Ozempic and Wegovy — both built on a peptide called semaglutide — have become cultural phenomena, mentioned in the same breath as Botox and Viagra. Eli Lilly's tirzepatide (sold as Mounjaro and Zepbound) is right behind them. Together, these drugs have created a market worth tens of billions of dollars and made "peptide" a household word.

But peptides are much more than weight loss drugs. Your body makes thousands of them. They tell your pancreas to release insulin. They signal pain. They trigger labor contractions. They fight bacteria. They regulate sleep, mood, appetite, and immunity. Before GLP-1 drugs ever hit the market, peptides were already running the show inside your body — you just didn't know their name.

So what exactly is a peptide? How does it differ from a protein? Why can some peptides shrink your waistline while others smooth wrinkles or speed up wound healing? This guide answers those questions from scratch. No biochemistry degree required. By the time you finish, you'll understand what peptides are, how they work, what they're used for, and where the science actually stands — separated from the hype.

Table of Contents

What Is a Peptide, Exactly?

Start with amino acids. These are small organic molecules — 20 standard ones in the human body — and they're the building blocks of all peptides and proteins. Think of amino acids as letters in an alphabet. String a few letters together and you get a word. String many words together and you get a sentence.

In molecular terms: a short chain of amino acids (roughly 2 to 50) is a peptide. A longer chain (50 or more) is generally called a protein. The bond holding each amino acid to the next is called a peptide bond, formed through a condensation reaction — one amino acid's carboxyl group (-COOH) reacts with another's amino group (-NH₂), releasing a water molecule and creating a sturdy CO-NH linkage.

That bond is surprisingly tough. Without enzymes to break it, a single peptide bond would take 350 to 600 years to degrade at room temperature. In your body, specialized enzymes called proteases do the job in seconds.

Each amino acid in the chain is called a "residue." The chain has two ends: the N-terminus (free amino group) and the C-terminus (free carboxyl group). Scientists always write peptide sequences from N-terminus to C-terminus, left to right.

The size hierarchy:

  • Dipeptide: 2 amino acids (example: carnosine)
  • Tripeptide: 3 amino acids (example: glutathione)
  • Oligopeptide: roughly 2–20 amino acids
  • Polypeptide: roughly 20–50+ amino acids
  • Protein: 50+ amino acids with complex 3D folding

The dividing line between "peptide" and "protein" is fuzzy. Insulin has 51 amino acids and is still routinely called a "peptide hormone." Glucagon has 29 amino acids and is definitely a peptide. The real functional difference matters more than the word count: proteins fold into elaborate three-dimensional structures and often work as enzymes or structural components. Peptides tend to stay flexible and work as messengers — chemical signals telling cells what to do.

Here's a useful way to think about the numbers. From just 20 amino acids, the possible combinations explode. A dipeptide (2 amino acids) has 400 possible sequences. A pentapeptide (5 amino acids) has 3.2 million. Your body selects from this vast menu to build the specific peptides it needs — each one folded and shaped to fit a particular receptor, like a key cut for one lock.

For a deeper look at the underlying chemistry, see our guide to amino acids and peptide bonds.

Peptides vs. Proteins: What's the Difference?

FeaturePeptideProtein
Size2–50 amino acids50+ amino acids
Molecular weightTypically under 5,000 Da5,000 to millions of Da
StructureUsually linear or simple cyclicComplex 3D folds (secondary, tertiary, quaternary)
Primary roleSignaling and communicationStructure, catalysis, transport, signaling
StabilityShorter-lived, rapidly degradedMore stable, longer-lasting
ExamplesOxytocin, GLP-1, endorphinsHemoglobin, collagen, antibodies
Drug deliveryOften injectable; some oral/topicalTypically injectable (biologics)

The key idea: proteins are the machinery. Peptides are the instructions. Your body uses peptides to tell proteins what to do, when to do it, and how much to make. Both are built from the same 20 amino acids — the difference is length, complexity, and function.

For an in-depth comparison, see peptide vs. protein: what's the difference?

How Peptides Work in the Body

Peptides are signaling molecules. They carry messages from one cell, tissue, or organ to another. The mechanism follows a lock-and-key pattern:

  1. A peptide is released (by your body or injected as a drug).
  2. It travels through the bloodstream or tissue fluid to its target.
  3. It binds to a specific receptor on the surface of a target cell. No match, no effect.
  4. The receptor activates and triggers an intracellular signaling cascade.
  5. Second messengers — small molecules like cyclic AMP (cAMP) and calcium ions — amplify the signal inside the cell.
  6. The cell responds. It might produce a protein, release a hormone, divide, migrate, or change its metabolism.

Most peptide receptors belong to a family called G protein-coupled receptors (GPCRs) — about 800 different cell-surface proteins that collectively are the target of roughly one-third of all approved drugs. When a peptide binds to a GPCR, it triggers a G protein on the inside of the cell membrane, which in turn activates downstream enzymes and ion channels.

Because peptides are water-soluble, they can't cross cell membranes on their own (unlike steroid hormones, which are fat-soluble and pass right through). This means peptide effects tend to be fast but short-lived: they hit the receptor, trigger the cascade, and are then broken down by enzymes in minutes to hours.

Your body already makes thousands of peptides. Here are a few you rely on every day:

  • Insulin tells cells to absorb glucose from the blood. Without it, blood sugar spikes dangerously — the core problem in type 1 diabetes.
  • Oxytocin triggers uterine contractions during labor and milk release during breastfeeding. It also plays a role in social bonding.
  • Endorphins bind to opioid receptors and block pain signals. The "runner's high" is partly endorphin-driven.
  • GLP-1 (glucagon-like peptide-1) is released from your gut after eating. It stimulates insulin, slows stomach emptying, and reduces appetite. Your natural GLP-1 lasts about 2 minutes before enzymes destroy it — which is why drug versions like semaglutide are engineered to last a full week.
  • Substance P transmits pain signals from sensory nerves to the brain.
  • Defensins punch holes in bacterial cell membranes as part of your innate immune defense.

One important distinction: peptide signaling is fast but temporary. Insulin spikes after a meal and clears within hours. Endorphins flood in during exercise and fade shortly after. This is by design — the body needs to turn these signals on and off quickly. It's also why most therapeutic peptides need repeated dosing (daily or weekly injections, for example), and why drug designers work hard to extend half-lives. Natural GLP-1 lasts 2 minutes. Semaglutide, through clever molecular modifications, lasts about 7 days.

For a detailed look at peptide signaling pathways and receptor types, see how peptides work: mechanisms of action explained.

The Major Types of Peptides

Peptides can be classified by academic criteria — size, structure, origin — but for practical purposes, it makes more sense to organize them by what they do.

Hormonal Peptides

These are the body's chemical messengers. They're produced by endocrine glands, released into the bloodstream, and act on distant target organs.

Major examples: insulin, glucagon, GLP-1, oxytocin, vasopressin (ADH), ACTH, gonadorelin (GnRH), and amylin. The hormonal peptide category includes the GLP-1 agonist drugs that have reshaped obesity treatment — tirzepatide, liraglutide, and exenatide among them.

Neuropeptides

Neuropeptides are produced by neurons and modulate nerve signaling. They're involved in pain perception, mood, appetite, stress responses, and more.

Key examples: endorphins, substance P, neuropeptide Y, CGRP (calcitonin gene-related peptide), and VIP (vasoactive intestinal peptide). The migraine drug class known as CGRP inhibitors — including erenumab (Aimovig) — works by blocking a neuropeptide pathway. See our neuropeptides overview for the full picture.

Antimicrobial Peptides (AMPs)

Your innate immune system uses short peptides to kill bacteria, fungi, and viruses. These antimicrobial peptides work by disrupting microbial cell membranes — essentially punching holes in invaders.

The main human AMPs are defensins and cathelicidins. LL-37 is the only human cathelicidin, and it's been studied extensively as a potential weapon against antibiotic-resistant bacteria. With drug-resistant infections killing over 1.2 million people per year globally (Lancet, 2022), AMPs represent one of the more promising angles of attack. For more, see antimicrobial peptides and antibiotic resistance.

Growth Hormone Peptides

These peptides stimulate your pituitary gland to produce and release growth hormone (GH). They're called "growth hormone secretagogues" — they don't contain GH themselves but rather tell your body to make more of it.

The main ones: CJC-1295 (a GHRH analog), ipamorelin (a selective GHRP), sermorelin (another GHRH analog), GHRP-2, GHRP-6 (another GHRH analog), hexarelin, tesamorelin (FDA-approved for HIV-associated lipodystrophy), and MK-677 (technically a non-peptide secretagogue, but grouped here because it acts on the same ghrelin receptor pathway). Learn more about the growth hormone axis in our GH axis guide.

Skincare Peptides

Cosmetic peptides applied topically to the skin fall into several functional categories:

  • Signal peptides like Matrixyl (palmitoyl pentapeptide-4) and Matrixyl 3000 tell fibroblasts to produce more collagen. A 2005 study in the International Journal of Cosmetic Science found Matrixyl reduced wrinkle depth by up to 36%.
  • Neurotransmitter-inhibiting peptides like Argireline (acetyl hexapeptide-3) and Snap-8 reduce muscle micro-contractions that cause expression lines. Think of them as a very mild topical cousin of Botox — though far less potent.
  • Carrier peptides like GHK-Cu deliver copper ions to skin cells, supporting collagen synthesis, antioxidant defense, and wound healing. GHK-Cu is backed by more than 50 years of published research.
  • Other notable skincare peptides: Syn-Ake (mimics temple viper venom to relax muscles), copper peptides (broad skin repair), and palmitoyl tripeptide-1 and related collagen-boosting signals.

Bioactive Food Peptides

When you digest protein — from milk, fish, soy, or meat — your body breaks it into amino acids and small peptides. Some of these fragments have biological activity of their own.

Collagen peptides (hydrolyzed collagen) are the most commercially significant. They're produced by breaking down collagen protein into smaller fragments, typically 2–20 amino acids long. When ingested, these fragments signal fibroblasts to ramp up collagen production. A 2019 meta-analysis in the Journal of Drugs in Dermatology pooling 11 studies and 805 patients found that collagen peptide supplementation improved skin hydration, elasticity, and wrinkle depth compared to placebo. This is the basis of the multi-billion-dollar collagen supplement industry.

Other bioactive food peptides: casein-derived peptides from dairy (particularly lactotripeptides IPP and VPP) have measurable blood-pressure-lowering effects in clinical trials. Fish-derived peptides show antioxidant properties. Soy peptides have been studied for cholesterol reduction. This is an active and growing area of food science research.

What Are Peptides Used For? Applications by Category

Weight Loss and Metabolic Health

This is where the money is — literally. The GLP-1 revolution has rewritten obesity medicine. Before 2005, drug-based weight loss topped out at 5-10% of body weight, and most drugs were pulled from the market for safety problems (fen-phen, sibutramine). The new peptide-based drugs doubled and tripled those numbers.

Semaglutide (sold as Ozempic for diabetes and Wegovy for weight loss) produces average body weight reductions of about 15% in clinical trials. It earned over $18 billion in global revenue in 2023 alone. Tirzepatide (Mounjaro/Zepbound), a dual GIP/GLP-1 agonist, hit even harder in the SURMOUNT-1 trial: participants lost an average of 22.5% of their body weight — roughly 52 pounds for someone starting at 230.

The next generation is already in trials. Retatrutide, a triple agonist targeting GLP-1, GIP, and glucagon receptors, showed up to 24% weight loss in Phase 2 data. CagriSema combines semaglutide with cagrilintide (an amylin analog) and is in Phase 3 trials.

Other peptides studied for metabolic health include liraglutide (Saxenda), dulaglutide (Trulicity), AOD-9604 (a modified fragment of human growth hormone), and exenatide (Byetta/Bydureon). For the full breakdown, see our guide to the best peptides for fat loss and our coverage of the GLP-1 obesity revolution.

Skincare and Anti-Aging

Peptide-based skincare is a multi-billion-dollar category. The approach is straightforward: apply short peptides to the skin that signal cells to produce more collagen, relax micro-contractions, or repair damage.

Does it work? The evidence is real, though more modest than marketing implies. Matrixyl has published clinical data showing wrinkle reduction. GHK-Cu has over five decades of research behind it. Argireline has studies showing reduced wrinkle depth when applied consistently.

The biggest limitation is penetration. Even small peptides struggle to cross the skin's outer barrier (stratum corneum) in large amounts. Concentration matters — many products contain peptides well below the levels used in clinical studies. For practical advice, see our best peptides for skin anti-aging guide.

Healing and Recovery

Two peptides dominate the injury-recovery space: BPC-157 and TB-500 (a synthetic fragment of thymosin beta-4).

BPC-157 is a 15-amino-acid peptide derived from a protective protein found in human gastric juice. In animal studies, it accelerates healing of tendons, ligaments, muscles, bone, and gut tissue. TB-500 promotes cell migration and blood vessel formation, also primarily in preclinical models. Human clinical trial data for both remains limited, though BPC-157 human trials are underway.

These two peptides are among the most popular in the self-directed peptide community, though regulators have taken notice. BPC-157 was included on the FDA's Category 2 list in 2023, raising questions about its future availability from compounding pharmacies.

For more on these peptides, see our guides to best peptides for wound healing and best peptides for joint health.

Muscle Growth and Athletic Performance

Growth hormone secretagogues — CJC-1295, ipamorelin, sermorelin, GHRP-2, GHRP-6 — work by increasing natural GH output. The idea is that more GH means better recovery, improved body composition, and potentially more muscle growth. IGF-1 LR3 is a modified version of insulin-like growth factor 1, which mediates many of GH's effects on muscle tissue. Follistatin inhibits myostatin, a protein that limits muscle growth.

Important context: peptides are not anabolic steroids. The muscle-building effects of GH secretagogues are more subtle — better recovery, improved body composition over months, some lean mass gains — rather than the dramatic bulk that anabolic steroids produce. Many users report the benefits are more about recovery and fat loss than raw muscle growth.

A word of caution: the World Anti-Doping Agency (WADA) prohibits growth hormone secretagogues, IGF-1, and related peptides in competitive sport. Athletes who test positive face suspensions. For the evidence-based picture, see best peptides for muscle growth and best peptides for athletic performance.

Immune Support

Thymosin alpha-1 is the most researched immune-modulating peptide. It's approved in over 35 countries (not the US) for hepatitis B, hepatitis C, and as an immune adjuvant. LL-37 has broad antimicrobial and immune-regulating properties. Thymalin is a thymic peptide studied primarily in Russian clinical settings. KPV is a tripeptide fragment of alpha-MSH with anti-inflammatory properties studied in gut inflammation models.

For the full rundown, see best peptides for immune support.

Brain Health and Cognition

Semax is a synthetic analog of ACTH(4-10) approved in Russia as a nootropic and for stroke recovery. Selank is a synthetic tuftsin analog approved in Russia for anxiety and cognitive support. Cerebrolysin is a mixture of neuropeptides derived from pig brain tissue, used in over 50 countries for stroke and traumatic brain injury. Dihexa is a newer research compound with striking preclinical data — it was reported to be 10 million times more potent than BDNF at promoting synapse formation in animal models, though human data is essentially nonexistent.

For more, see best peptides for cognitive enhancement and best peptides for anxiety and stress.

Sexual Health

PT-141 (bremelanotide, brand name Vyleesi) is FDA-approved for hypoactive sexual desire disorder in premenopausal women. It works through melanocortin receptors in the brain — a completely different mechanism from drugs like Viagra, which work on blood flow. Kisspeptin regulates the reproductive hormone cascade and is being studied for both fertility and sexual arousal. For the research summary, see best peptides for sexual health.

Sleep and Recovery

DSIP (delta sleep-inducing peptide) is a nine-amino-acid neuropeptide first isolated from rabbit brain in 1977. It's been studied for its effects on sleep architecture, though the clinical evidence is mixed and mostly from older studies. For the available data, see best peptides for sleep.

Other peptides studied in the recovery and longevity space include epitalon (studied for telomerase activation), humanin and MOTS-c (mitochondrial-derived peptides), and SS-31 (elamipretide, which targets mitochondrial cardiolipin). The mitochondrial peptides are a newer discovery — humanin was first identified in 2001, MOTS-c in 2015 — and represent an intriguing frontier in aging research. See best peptides for gut health and best peptides for inflammation reduction for related categories.

Longevity and Anti-Aging

Beyond skincare, several peptides are being studied for systemic anti-aging effects. Epitalon is a four-amino-acid peptide that Russian researcher Vladimir Khavinson has studied since the 1980s for its ability to activate telomerase, the enzyme that maintains telomere length. Melanotan II was originally developed for tanning (it stimulates melanin production) but carries significant safety concerns including nausea and cardiovascular effects. Angiotensin 1-7 and natriuretic peptides are studied for cardiovascular protection. The longevity peptide space is heavy on preclinical promise and light on clinical proof — but the interest is real and the research is accelerating. For a broader look, see best peptides for cardiovascular health and best peptides for hair growth.

FDA-Approved Peptide Drugs

Over 100 peptide-based drugs have received FDA approval. Here are some of the most significant:

Drug (Brand Name)PeptideIndicationApproval
Ozempic / Wegovy / RybelsusSemaglutideType 2 diabetes, obesity2017 / 2021 / 2019
Mounjaro / ZepboundTirzepatideType 2 diabetes, obesity2022 / 2023
Victoza / SaxendaLiraglutideType 2 diabetes, obesity2010 / 2014
TrulicityDulaglutideType 2 diabetes2014
Byetta / BydureonExenatideType 2 diabetes2005 / 2012
Humulin / Humalog / LantusInsulin analogsDiabetes1982+
ForteoTeriparatideOsteoporosis2002
LupronLeuprolideProstate cancer, endometriosis1985
SandostatinOctreotideAcromegaly, carcinoid tumors1988
PitocinOxytocin (synthetic)Labor induction1980
DDAVPDesmopressinDiabetes insipidus, bedwetting1978
EgriftaTesamorelinHIV-associated lipodystrophy2010
VyleesiBremelanotide (PT-141)HSDD in premenopausal women2019
AimovigErenumabMigraine prevention2018
LutatheraLutetium-177 dotatateNeuroendocrine tumors2018
ScenesseAfamelanotideErythropoietic protoporphyria2019

Between 2016 and 2024, 34 new peptide drugs received FDA approval. Over 170 peptide candidates are currently in clinical trials. For the complete database, see our FDA-approved peptide drug list.

The Peptide Market: A $50 Billion Industry

The peptide therapeutics market hit roughly $49–53 billion in 2025, driven overwhelmingly by GLP-1 drugs. Semaglutide alone generated over $18 billion in 2023 revenue for Novo Nordisk. Tirzepatide brought in another $5.2 billion for Eli Lilly in the same year — and that was before its obesity indication (Zepbound) launched.

Market projections vary, but most analysts forecast $70–87 billion by 2031–2035. The growth is coming from several directions: next-generation GLP-1 drugs (retatrutide, CagriSema, orforglipron), expanded indications for existing drugs (semaglutide is being tested for Alzheimer's, NASH, kidney disease, and addiction), and new peptide categories reaching the market.

The competitive picture is intense. Novo Nordisk and Eli Lilly are the dominant players, but dozens of companies are racing to develop oral GLP-1 alternatives, longer-acting formulations, and multi-target agonists. For the full market breakdown, see our peptide therapeutics market forecast and the Novo Nordisk vs. Eli Lilly market war analysis.

The cosmetic peptide market is a separate story — also growing, driven by consumer demand for science-backed skincare ingredients. The global peptide skincare market is expected to exceed $5 billion by 2028.

Beyond the big pharma numbers, there's a substantial but harder-to-measure market in compounded peptides, research peptides, and peptide-based supplements. Before the 2023 crackdown, compounded semaglutide alone was estimated to be a $1 billion+ annual market. Collagen peptide supplements — a consumer-friendly product category requiring no prescription — generated several billion dollars globally. The peptide economy is larger than any single market report captures.

Peptide Safety: What the Research Shows

Peptides, as a class, don't have a single safety profile. That's like asking "are medicines safe?" It depends entirely on which peptide, what dose, what route, and who's taking it.

FDA-approved peptide drugs have been through Phase I, II, and III clinical trials. Their safety profiles are well-documented. For GLP-1 drugs specifically, the most common side effects are gastrointestinal: nausea (reported in 20–44% of semaglutide patients in STEP trials), vomiting, diarrhea, and constipation. These effects are usually dose-dependent and tend to diminish over weeks. Rare but serious risks include pancreatitis, gallbladder disease, and (in animal studies) thyroid C-cell tumors — though the thyroid risk has not been confirmed in humans after years of monitoring.

Growth hormone peptides (CJC-1295, ipamorelin, GHRP-2, GHRP-6) can cause water retention, joint pain, carpal tunnel symptoms, increased hunger (especially GHRP-6), and in some cases elevated blood sugar or cortisol. Long-term safety data from controlled human trials is limited for most of these compounds.

Research peptides — compounds like BPC-157, TB-500, and many nootropic peptides — have extensive animal data but limited or no controlled human trial results. The safety picture is incomplete. This doesn't mean they're dangerous, but it does mean the usual assurances about safety profiles don't apply.

Compounded peptides carry an additional risk layer: quality control. Unlike FDA-approved drugs manufactured under strict Good Manufacturing Practice (GMP) conditions, compounded peptides vary in purity, potency, and sterility depending on the pharmacy. The FDA has flagged this as a public health concern, particularly for compounded semaglutide.

Skincare peptides are generally well-tolerated. Irritation is possible, especially with high concentrations or when combined with active acids, but serious adverse effects from topical peptide products are rare.

The universal rule: work with a doctor. This applies to FDA-approved peptides (which require prescriptions) and is doubly true for anything that hasn't gone through the approval process. For a deep dive into safety data by compound, see are peptides safe? everything you need to know and the peptide side effects database.

Peptide regulation has shifted dramatically since 2023, and it continues to move. Here's the current state of play.

FDA-approved peptide drugs follow the same pathway as any other pharmaceutical: preclinical studies, IND application, Phase I/II/III clinical trials, NDA or BLA submission, and FDA review. Over 100 peptide drugs have cleared this process. No controversy here.

The compounding crackdown. Under Section 503A and 503B of the Federal Food, Drug, and Cosmetic Act, compounding pharmacies can prepare custom medications — including peptides — for individual patients. But the FDA has been tightening the rules. In late 2023, the agency designated 17 peptides as "Category 2," meaning it found they present "demonstrable difficulties" for compounding. The list included BPC-157, thymosin alpha-1, thymosin beta-4, and others. In September 2023, GHK-Cu injectable was specifically restricted. In February 2026, the FDA announced its intent to further restrict GLP-1 compounding after previously allowing it during the semaglutide shortage.

This matters because compounded peptides had become a massive market — millions of Americans were getting compounded semaglutide at a fraction of branded Ozempic's price. The GLP-1 compounding ban has sparked lawsuits, Congressional attention, and significant patient disruption.

Research peptides. Peptides sold "for research purposes only" or "not for human consumption" exist in a legal gray area. They are legal to buy and sell for legitimate laboratory research. They are not approved for human use. Many people buy them for self-administration anyway, which puts them in murky regulatory territory. The FDA has sent warning letters to companies marketing research peptides with implied human-use claims.

WADA prohibitions. The World Anti-Doping Agency bans growth hormone secretagogues (CJC-1295, ipamorelin, GHRP-2, GHRP-6, MK-677), IGF-1, and various other peptides in competitive sport. Athletes who test positive face two- to four-year suspensions. See our WADA peptide rules guide for specifics.

Cosmetic peptides — those in skincare products — are regulated as cosmetics, not drugs. They don't require FDA pre-market approval. They can't make drug claims ("treats wrinkles") but can make cosmetic claims ("reduces the appearance of fine lines").

How Peptides Are Taken

Peptides enter the body through several routes, each with trade-offs.

Subcutaneous injection — The most common route for therapeutic peptides. A small needle goes into the fat layer under the skin (usually the abdomen or thigh). Semaglutide, tirzepatide, BPC-157, and most GH secretagogues are administered this way. Absorption is reliable and bypasses the digestive system entirely. The downside: needles. Most people get used to it, but it's still a barrier for many.

Oral administration — Historically, this was considered impossible for peptides because stomach acid and digestive enzymes destroy them. Oral bioavailability for unmodified peptides is typically below 1%. But breakthroughs are changing this. Oral semaglutide (Rybelsus) uses a permeation enhancer called SNAC (sodium N-[8-(2-hydroxybenzoyl)amino] caprylate) to protect the peptide and boost absorption. It must be taken on an empty stomach with minimal water. Orforglipron, a non-peptide oral GLP-1 agonist in late-stage trials, sidesteps the problem entirely by using a small molecule that mimics a peptide's effect. Collagen peptide supplements are a different story — they're designed to be partially broken down during digestion, with the resulting fragments providing the biological signal.

Topical application — Skincare peptides are applied to the skin as serums, creams, and masks. Penetration through the stratum corneum is the main challenge. Peptide size, formulation, and concentration all affect how much actually reaches the target cells.

Nasal sprays — Selank and semax are commonly administered intranasally, which offers rapid absorption through the mucous membranes and some degree of direct access to the brain via the olfactory pathway. Desmopressin (DDAVP) is another nasally administered peptide, used for diabetes insipidus and bedwetting. The nasal route avoids first-pass metabolism by the liver, which destroys many peptides before they reach systemic circulation.

The delivery challenge is a major area of ongoing research. Scientists are working on peptide patches, implants, inhalable formulations, and improved oral delivery systems. If oral peptide delivery is cracked at scale, it would be a game-changer for patient compliance and market growth. For now, injections remain the gold standard for most therapeutic peptides.

A Brief History of Peptide Science

Peptide science stretches back over 120 years. Here are the milestones that matter.

1902 — William Bayliss and Ernest Starling discover secretin, the first hormone ever identified. It's a peptide produced in the small intestine that stimulates the pancreas to secrete digestive juices. This discovery launched the entire field of endocrinology.

1921 — Frederick Banting and Charles Best extract insulin from dog pancreases at the University of Toronto. Within a year, they're using it to treat diabetic patients. Banting wins the Nobel Prize in 1923. Insulin — a 51-amino-acid peptide — becomes the first peptide drug and one of the most important medical discoveries of the 20th century.

1951 — Frederick Sanger determines the complete amino acid sequence of insulin, proving that proteins have defined, specific sequences. He wins the Nobel Prize in 1958.

1953 — Vincent du Vigneaud synthesizes oxytocin in the laboratory — the first peptide hormone ever made synthetically. Nobel Prize, 1955.

1963 — Robert Bruce Merrifield invents solid-phase peptide synthesis (SPPS), a revolutionary technique that lets chemists build peptides one amino acid at a time on a solid support. Before SPPS, synthesizing even a short peptide took months. Merrifield's method cut it to days. Nobel Prize, 1984. SPPS remains the foundation of peptide manufacturing today.

1982 — Recombinant human insulin (Humulin) becomes the first FDA-approved product of recombinant DNA technology. Goodbye, pig and cow pancreas extraction.

2005 — Exenatide (Byetta) becomes the first GLP-1 receptor agonist approved by the FDA. It's based on exendin-4, a peptide found in Gila monster saliva. Yes, a lizard.

2017 — Semaglutide (Ozempic) receives FDA approval for type 2 diabetes. It's a modified GLP-1 analog with a once-weekly dosing schedule.

2021 — Semaglutide is approved as Wegovy for chronic weight management. The STEP trials show ~15% body weight loss. The obesity drug market is transformed overnight.

2022 — Tirzepatide (Mounjaro) is approved. It targets both GLP-1 and GIP receptors — the first dual agonist. SURMOUNT-1 will later show 22.5% weight loss.

2023–2026 — The FDA tightens peptide compounding regulations. Triple agonists (retatrutide) and combination therapies (CagriSema) enter Phase 3 trials. Oral GLP-1 drugs advance toward approval. The peptide market crosses $50 billion.

The recurring theme in this timeline: peptide science moves slowly for decades, then suddenly reshapes entire medical fields. Insulin did it for diabetes in the 1920s. GLP-1 drugs are doing it for obesity right now. The question is which peptide category breaks through next.

For the full timeline, see our history of peptide discovery.

Frequently Asked Questions

Are peptides the same as proteins?

No. Peptides and proteins are both chains of amino acids, but peptides are shorter (roughly 2–50 amino acids) and proteins are longer (50+). Proteins fold into complex 3D structures and often work as enzymes or structural materials. Peptides are usually simpler, more flexible, and primarily work as signaling molecules. The boundary is blurry — insulin has 51 amino acids and is commonly called a peptide — but the functional distinction holds.

Are peptides steroids?

No. Steroids are lipid-based molecules derived from cholesterol (think testosterone, estrogen, cortisol). Peptides are chains of amino acids. They have completely different chemical structures, different mechanisms of action, and different regulatory classifications. Calling peptides "steroids" is like calling a bicycle a boat because both are vehicles.

Are peptides safe?

It depends on the peptide. FDA-approved peptide drugs (insulin, semaglutide, tirzepatide, leuprolide, etc.) have documented safety profiles from clinical trials and years of real-world use. Research peptides and compounded preparations have less data. Side effects vary widely by compound. The safest approach: work with a healthcare provider and use pharmaceutical-grade products when possible.

What are the side effects of peptides?

Side effects are peptide-specific. GLP-1 drugs commonly cause nausea, vomiting, and diarrhea (usually temporary). Growth hormone peptides can cause water retention, joint pain, and increased appetite. BPC-157 and TB-500 have limited human safety data. Injection-site reactions (redness, swelling, itching) are common across most injectable peptides. See our peptide side effects database for compound-specific information.

Do peptides help with weight loss?

GLP-1 agonists do — dramatically. Semaglutide (Wegovy) produces ~15% body weight loss on average. Tirzepatide (Zepbound) produces ~22.5%. These are prescription drugs with strong clinical trial evidence. Other peptides marketed for weight loss (AOD-9604, various GH secretagogues) have far weaker evidence.

Can you buy peptides over the counter?

Some. Collagen peptide supplements and peptide-containing skincare products are available without a prescription. Therapeutic peptides — GLP-1 drugs, growth hormone peptides, etc. — require a prescription in the US. "Research peptides" can be purchased from online suppliers but are sold for research use only and are not approved for human consumption. See our guide on OTC peptide availability.

FDA-approved peptide drugs are legal with a prescription. Cosmetic peptides in skincare are legal to buy and use. Research peptides are legal to purchase for laboratory research. Using research peptides on yourself falls into a gray area — not explicitly illegal for the buyer in most jurisdictions, but the seller cannot legally market them for human use. Some peptides are banned in competitive sport by WADA. Import regulations vary by country. For details, see our peptide legality guide.

How long do peptides take to work?

Wildly variable. GLP-1 drugs typically show measurable weight loss within 4–8 weeks, with full effects at 6–12 months. Skincare peptides like Matrixyl need 8–12 weeks of consistent daily use to show visible results. BPC-157 users (in anecdotal reports) describe effects within 1–4 weeks for injury recovery. Growth hormone peptides typically take 4–12 weeks for body composition changes. The answer always depends on the specific peptide, the dose, and what you're measuring. For detailed timelines, see how long do peptides take to work.

What is the difference between peptides and amino acids?

An amino acid is a single molecule — one building block. A peptide is a chain of amino acids linked by peptide bonds (minimum two). When you take a "BCAA supplement" (branched-chain amino acids), you're getting individual amino acids. When you take a collagen peptide supplement, you're getting chains of amino acids that carry biological signals your cells can read. The difference matters: free amino acids and peptides are absorbed differently, act through different mechanisms, and have different biological effects. For more, see the difference between peptides and amino acids.

The Bottom Line

Peptides are short chains of amino acids that work as your body's messaging system. They tell cells to absorb glucose, fight infection, feel pain, build collagen, release growth hormone, and do a thousand other things. Your body makes thousands of them. Scientists have learned to make more — including drugs that have transformed diabetes treatment, reshaped the weight loss industry, and opened new frontiers in everything from skincare to neurology.

The field has real limitations. Most peptides can't be taken orally (yet). Long-term data is scarce for many popular compounds. The regulatory picture is shifting. Marketing hype regularly outpaces clinical evidence, especially for peptides that haven't gone through FDA approval.

But the trajectory is unmistakable. Over 100 peptide drugs approved. Over 170 in clinical trials. A market approaching $50 billion. AI-driven peptide discovery accelerating the pipeline. And millions of people — patients, consumers, athletes, biohackers — paying attention for the first time.

This article is your starting point. From here, go deeper: our peptide glossary defines every term you'll encounter, our amino acids and peptide bonds primer covers the chemistry, and our individual peptide profiles give you the research behind each compound.

References

  1. National Center for Biotechnology Information. "Biochemistry, Peptide." StatPearls. Updated 2024. https://www.ncbi.nlm.nih.gov/books/NBK562260/

  2. Wang L, et al. "Therapeutic peptides: current applications and future directions." Signal Transduction and Targeted Therapy. 2022;7:48. https://www.nature.com/articles/s41392-022-00904-4

  3. Muttenthaler M, et al. "Trends in peptide drug discovery." Nature Reviews Drug Discovery. 2021;20(4):309–325. https://pubmed.ncbi.nlm.nih.gov/33536635/

  4. Al Musaimi O. "FDA TIDES (Peptides and Oligonucleotides) Harvest." Pharmaceuticals. 2025;18(3):291. https://pmc.ncbi.nlm.nih.gov/articles/PMC11945313/

  5. Wilding JPH, et al. "Once-weekly semaglutide in adults with overweight or obesity (STEP 1)." New England Journal of Medicine. 2021;384:989–1002. https://pubmed.ncbi.nlm.nih.gov/33567185/

  6. Jastreboff AM, et al. "Tirzepatide once weekly for the treatment of obesity (SURMOUNT-1)." New England Journal of Medicine. 2022;387:205–216. https://pubmed.ncbi.nlm.nih.gov/35658024/

  7. Robinson S, et al. "Palmitoyl pentapeptide provides improvement in photoaged human facial skin." International Journal of Cosmetic Science. 2005;27:155–160. https://pubmed.ncbi.nlm.nih.gov/18492182/

  8. Merrifield RB. "Solid phase peptide synthesis. I. The synthesis of a tetrapeptide." Journal of the American Chemical Society. 1963;85(14):2149–2154.

  9. Sanger F, Tuppy H. "The amino-acid sequence in the phenylalanyl chain of insulin." Biochemical Journal. 1951;49(4):463–481. https://pmc.ncbi.nlm.nih.gov/articles/PMC1197535/

  10. Grand View Research. "Peptide Therapeutics Market Size & Industry Report, 2030." https://www.grandviewresearch.com/industry-analysis/peptide-therapeutics-market

  11. Murray CJL, et al. "Global burden of bacterial antimicrobial resistance in 2019." The Lancet. 2022;399(10325):629–655.

  12. U.S. Food and Drug Administration. "Compounding and the FDA: Questions and Answers." https://www.fda.gov/drugs/human-drug-compounding/compounding-and-fda-questions-and-answers

  13. Pickart L, Vasquez-Soltero JM, Margolina A. "GHK Peptide as a Natural Modulator of Multiple Cellular Pathways in Skin Regeneration." BioMed Research International. 2015;2015:648108. https://pubmed.ncbi.nlm.nih.gov/26236730/