What Are Peptides? A Plain Explanation, and What They Are Used For Medically

There are twenty standard amino acids, each with the same backbone and a side chain that gives it its character. When the carboxyl group of one joins the amino group of the next, a molecule of water is released and the two are linked by an amide bond, called in this context a peptide bond. The chain it builds is a peptide.

Two amino acids make a dipeptide; three make a tripeptide. GHK-Cu and KPV are both tripeptides. Ipamorelin is five amino acids, oxytocin nine, BPC-157 fifteen, sermorelin twenty-nine, semaglutide thirty-one. The order of amino acids along the chain, the sequence, is what makes one peptide different from another.

The boundary is a convention. Most textbooks and regulators put it around 40 to 50 amino acids; the FDA's working definition treats a chain of 40 or fewer as a peptide and anything longer as a protein. Insulin sits on the line at 51 amino acids in two chains held together by disulfide bridges, which is why it is called a peptide hormone in one book and a small protein in the next. Both are correct.

What length implies matters more than the number. A short chain does not fold into the stable shape a protein has; it is flexible, usually water-soluble, and quickly cut apart by the enzymes the body keeps everywhere for that purpose. Above the boundary sit biologics such as growth hormone, at 191 amino acids, and monoclonal antibodies, made by living cells. A peptide under about forty amino acids can be built by chemical synthesis one amino acid at a time, which is why a state-licensed pharmacy can obtain one as a bulk powder with a certificate of analysis and compound it, while nobody compounds an antibody. It is also why growth hormone itself and the growth-hormone-releasing peptides below are different things, regulated differently.

A conventional drug like ibuprofen or metformin is a small molecule, usually under about 900 daltons, built by organic chemistry rather than from amino acids. Small molecules can be made to survive the stomach, cross cell membranes and last for hours or days, which is why most are tablets. Their weakness is selectivity: a small molecule fits into a binding pocket, and similar pockets exist on proteins the drug was never meant to touch.

A peptide is typically 500 to 5,000 daltons and binds the way the body's own signal binds, across a broad surface rather than into a pocket, which tends to make it highly selective for its receptor. A 2021 review in Nature Reviews Drug Discovery counted more than eighty peptide drugs approved worldwide and described that selectivity, low tissue accumulation and a metabolic fate that is simply amino acids as the reasons interest in the class keeps growing. The trade-off is that a peptide generally cannot be swallowed and is cleared quickly.

A native peptide is one the body makes: insulin, GLP-1, oxytocin. A synthetic peptide is a manufactured copy, either of the native sequence exactly, as with oxytocin, or of a fragment, as with sermorelin, the first 29 amino acids of the 44-amino-acid growth-hormone-releasing hormone. An analogue has been deliberately altered, an amino acid swapped or a fatty acid attached, so the peptide resists breakdown or binds differently; semaglutide and tirzepatide are analogues. BPC-157 is a synthetic sequence derived from a protein found in gastric juice, and GHK-Cu is a native fragment found in blood plasma.

Beta cells in the pancreas release insulin when blood glucose rises; it binds insulin receptors on muscle, liver and fat cells, and those cells take up glucose. It was the first peptide used as a medicine, from 1922, and a 2018 review in Bioorganic and Medicinal Chemistry traces the history of peptide therapeutics from that point. It illustrates the general rule: the peptide is the message, the receptor is the reader, and the cell's response is whatever that cell is built to do when it hears the message.

Glucagon-like peptide-1 is a 30-amino-acid peptide released by cells in the lining of the small intestine within minutes of a meal. It tells the pancreas to release insulin only when glucose is high, slows stomach emptying, and acts on receptors in the hypothalamus and brainstem that register fullness. Glucose-dependent insulinotropic polypeptide, GIP, is a 42-amino-acid peptide with an overlapping role. Native GLP-1 is destroyed by the enzyme DPP-4 within about two minutes, which is why a drug copy has to be engineered rather than simply injected. Semaglutide is a GLP-1 receptor agonist; tirzepatide acts at both the GIP and GLP-1 receptors.

Growth hormone is not released continuously. The hypothalamus sends growth-hormone-releasing hormone to the pituitary in pulses, the largest during deep sleep early in the night, and the pituitary answers with a pulse of growth hormone. Ghrelin, made mostly in the stomach, acts on a different pituitary receptor to amplify the same release; somatostatin switches it off. Sermorelin and tesamorelin are GHRH analogues, ipamorelin and hexarelin are ghrelin-receptor agonists, and CJC-1295 is a GHRH analogue modified to last longer. All of them add to the pulse the body already makes. None of them is growth hormone.

Oxytocin and vasopressin are cyclic nine-amino-acid peptides made in the hypothalamus and released from the posterior pituitary. Vasopressin governs water retention and blood pressure. Oxytocin triggers uterine contraction and milk let-down and is released during touch, orgasm and social contact, which is where its reputation as a bonding hormone comes from; the same molecule acts on smooth muscle in the uterus and on neurons in the amygdala.

Many peptides act locally rather than through the blood. Thymosin beta-4, the parent of TB-500, is inside almost every cell binding actin and governing how cells move; a 2005 review in Trends in Molecular Medicine described it moonlighting as a repair signal after injury. Thymosin alpha-1, the molecule in Thymosin Alpha-1, is a 28-amino-acid thymic peptide that modulates T-cell maturation. Kisspeptin is the upstream switch for the reproductive axis; a 2005 paper in the Journal of Clinical Endocrinology and Metabolism reported that a kisspeptin-54 infusion raised luteinizing hormone, follicle-stimulating hormone and testosterone in healthy men.

Whatever the peptide, the body clears it deliberately fast. Peptidases in blood, kidney and tissue cut it apart within minutes and the fragments are recycled as amino acids; a signal that lingered would be one the body could not turn off. That is the central engineering problem for a peptide drug.

These are the most studied peptides in medicine and the only ones on this page with large randomized trials for the use they are prescribed for. STEP 1, in the New England Journal of Medicine in 2021, randomized 1,961 adults with overweight or obesity and no diabetes to weekly semaglutide or placebo for 68 weeks alongside lifestyle intervention and reported a mean weight change of about 15 percent against about 2 percent on placebo. SELECT, in the same journal in 2023, followed more than 17,000 adults with established cardiovascular disease and overweight or obesity and reported a 20 percent lower rate of major adverse cardiovascular events on semaglutide. SURMOUNT-1, in the New England Journal of Medicine in 2022, reported mean weight reductions of up to about 21 percent at the highest tirzepatide dose over 72 weeks, and SURMOUNT-2 in the Lancet in 2023 reported similar findings in adults with type 2 diabetes. Both molecules also exist as FDA-approved manufactured products, covered below. What is semaglutide, what is tirzepatide and semaglutide vs tirzepatide go deeper.

These prompt the pituitary to release growth hormone in a pulse rather than replacing it. A 1997 paper in the Journal of Clinical Endocrinology and Metabolism reported that long-term GHRH(1-29) injection raised growth hormone and IGF-1 in healthy older adults, and a 1997 paper in Metabolism reported the same for nightly injections in older men. Ipamorelin was characterized in the European Journal of Endocrinology in 1998 as the first selective growth hormone secretagogue, and CJC-1295 was shown in the Journal of Clinical Endocrinology and Metabolism in 2006 to raise growth hormone and IGF-1 for days after a single dose in healthy adults. Tesamorelin has the strongest trial record in the group: a 2007 trial in the New England Journal of Medicine in adults with HIV-associated abdominal fat accumulation reported roughly a 15 percent reduction in visceral fat over 26 weeks against a small increase on placebo, and a 2014 trial in JAMA reported reductions in visceral and liver fat in the same population. The catalog carries sermorelin, CJC-1295 / ipamorelin, tesamorelin and combinations of them.

BPC-157 is the peptide most searched for after the GLP-1s, and its evidence is animal and cell research: a 2006 paper in the Journal of Orthopaedic Research described faster reattachment after Achilles detachment in rats, a 2014 paper in Molecules described increased growth hormone receptor expression in cultured tendon fibroblasts, and a 2011 review in Current Pharmaceutical Design covers the gastrointestinal work it was first studied for. There are no randomized human trials of BPC-157. TB-500 is a fragment of thymosin beta-4; the parent molecule has been through a placebo-controlled safety study in healthy volunteers, but TB-500 itself has no randomized human trials. KPV was described in Gastroenterology in 2008 reducing intestinal inflammation in mouse models; no randomized human trials exist. All three are on the catalog, singly and as the BPC-157 + TB-500 preparation, and peptides for healing compares them.

GHK-Cu is a copper-binding tripeptide found in human plasma that declines with age. A 1988 paper in FEBS Letters reported it stimulating collagen synthesis in cultured fibroblasts, and a 2015 review in BioMed Research International summarizes the cell and animal work since. Human trials of injectable GHK-Cu have not been published; the human data is for topical cosmetic use. See GHK-Cu and peptides for skin.

Both were developed in Russia and are on the catalog as injections and as Selank and Semax nasal sprays. Selank, a tuftsin analogue, was reported in a 2008 Russian clinical paper to have anxiolytic effects in adults with generalized anxiety disorder and neurasthenia; Semax, an ACTH(4-10) analogue, was described in Brain Research in 2006 regulating BDNF and its receptor in the rat hippocampus. Neither has large randomized trials published in Western journals.

PT-141 is bremelanotide, a melanocortin receptor agonist that acts in the brain rather than on blood flow, and it has an approved counterpart: randomized, placebo-controlled trials in premenopausal women with hypoactive sexual desire disorder were published in Women's Health in 2016 and Obstetrics and Gynecology in 2019. Oxytocin is the native hormone; a 2014 crossover study in Hormones and Behavior examined intranasal oxytocin in couples, and the human literature for intimacy beyond that is small. Kisspeptin has the 2005 infusion data in men described above. Peptides for libido sets these side by side.

MOTS-c is a 16-amino-acid peptide encoded in mitochondrial DNA; a 2015 paper in Cell Metabolism reported it improving metabolic measures in mice, and no randomized human trials exist. NAD+ is not a peptide but a coenzyme, prescribed alongside peptides as an injection and a nasal spray; a 2012 paper in PLOS ONE reported that NAD+ in human tissue declines with age. Thymosin Alpha-1 has more human study than most peptides here; a 2020 review in the World Journal of Virology summarizes trials in hepatitis B and C and as a vaccine adjuvant, and the molecule is licensed as a drug in a number of countries outside the United States. It is not FDA approved.

Several products in the same catalog are vitamins or nutrients: methylcobalamin, the active form of B12, L-carnitine, glutathione and the Lipo-B combination. Glutathione is technically a tripeptide but works as a metabolic antioxidant rather than a signal; a 2015 randomized trial in the European Journal of Nutrition studied it as an oral supplement. They are listed together because they are prescribed and injected the same way, not because they work the same way.

An approved drug has been through clinical trials, an FDA review of its safety, effectiveness and manufacturing, and is made in a licensed facility to the specification on its label. Semaglutide is approved for chronic weight management and to reduce major adverse cardiovascular events in adults with cardiovascular disease and overweight or obesity under NDA 215256. Tirzepatide is approved for chronic weight management and for moderate to severe obstructive sleep apnea in adults with obesity under NDA 217806. Bremelanotide, the molecule in PT-141, is approved for premenopausal women with acquired, generalized hypoactive sexual desire disorder under NDA 210557. Tesamorelin is approved under BLA 022505 for the reduction of excess abdominal fat in adults with HIV and lipodystrophy, and its label states it is not indicated for weight loss management. Oxytocin has been an approved injectable for obstetric use for decades.

Approval attaches to a specific product, not to a molecule. A compounded preparation of the same molecule is not covered by it.

Compounding is the preparation of a medication by a licensed pharmacist for an individual patient against a prescription, governed by section 503A of the Federal Food, Drug, and Cosmetic Act. The FDA is direct about what it is: "Compounded drugs are not FDA-approved. This means that FDA does not verify the safety, effectiveness or quality of compounded drugs before they are marketed." Drugs compounded under 503A are not subject to the federal manufacturing standards that apply to approved drugs and to 503B outsourcing facilities; they are regulated primarily by state boards of pharmacy.

The statute sets the conditions. A compounded drug must be "compounded for an identified individual patient based on the receipt of a valid prescription order", by "a licensed pharmacist in a State licensed pharmacy or a Federal facility, or a licensed physician". It may not be a product "withdrawn or removed from the market" for safety, and a pharmacy may not compound "regularly or in inordinate amounts" a drug that is "essentially a copy of a commercially available drug product". Every prescription peptide Pepti dispenses is prepared this way, by a state-licensed, FDA-registered pharmacy, to a prescription written for you by a physician licensed in your state. The quality page and lab results show the pharmacy identity and certificates of analysis behind that.

The statute also says which raw materials a 503A pharmacy may compound from. A bulk drug substance must "comply with the standards of an applicable United States Pharmacopoeia or National Formulary monograph", be a component of an FDA-approved drug, or "appear on a list developed by the Secretary", the 503A Bulks List. The FDA's page on the framework, updated 14 May 2026, restates the three routes, adds that every bulk substance must come with a valid certificate of analysis from an FDA-registered establishment, and explains that the Bulks List is built by rulemaking after nominations are reviewed with the Pharmacy Compounding Advisory Committee.

Semaglutide, tirzepatide, tesamorelin, bremelanotide and oxytocin qualify through the second route, as components of approved drugs. Most other peptides on this page were nominated for the Bulks List and sit under the FDA's interim policy while that review runs.

Because the Bulks List has been built slowly, the FDA's interim policy sorts nominated substances into three categories. In its words: Category 1 is "Bulk Drug Substances Under Evaluation", where the FDA does not intend to take enforcement action against compounding that meets its conditions; Category 2 is "Bulk Drug Substances that Raise Significant Safety Concerns"; Category 3 is "Bulk Drug Substances Nominated Without Adequate Support". The version in force as this page is written is dated 14 May 2026. On it, methylcobalamin, NAD, glutathione and GHK-Cu for non-injectable routes sit in Category 1; Category 2 is now six substances, none of them a peptide removed in April; cibinetide, the molecule in ARA-290, sits in Category 3. The FDA has also said that since 7 January 2025 it no longer places newly nominated substances into these categories at all.

From 2023 until April 2026, BPC-157, TB-500, KPV, injectable GHK-Cu and eight other peptides sat in Category 2. On 15 April 2026 the FDA announced it was removing twelve peptides from Category 2 because their nominations had been withdrawn, effective about a week later, and stated that removal "does not, by itself, place these substances on the 503A bulks list or into Category 1". The FDA's safety-risk page, current as of 22 April 2026, now shows them under nominations that were withdrawn rather than in Category 2.

The Pharmacy Compounding Advisory Committee then met on 23 and 24 July 2026 to consider seven of them for the Bulks List: BPC-157, KPV, TB-500 and MOTS-c on the first day, emideltide (DSIP), Semax and epitalon on the second, each as the free base and the acetate. It voted to recommend adding BPC-157, KPV and TB-500 by 8 to 6 with one abstention each, MOTS-c by 7 to 5, epitalon by 7 to 4 and Semax by 8 to 5, and voted 6 to 7 against emideltide. A committee vote is a non-binding recommendation; the FDA issues its own determination and then adds a substance by notice-and-comment rulemaking, which had not happened for any of them as of September 2026. GHK-Cu was not on the July agenda; the FDA intends to consult the committee on it before the end of February 2027.

The accurate summary for the peptides most people ask about: no longer flagged as a safety concern, recommended for the positive list by the advisory committee, awaiting the FDA's final action, and still not FDA-approved drugs, because compounded medications never are. Are peptides FDA approved and are peptides legal in the US keep this current.

Because approved versions exist, compounded semaglutide and tirzepatide are governed by the "essentially a copy" rule rather than the Bulks List. The FDA declared the tirzepatide shortage resolved on 19 December 2024 and the semaglutide shortage on 21 February 2025, and the periods during which it declined to enforce against 503A compounding of copies ended on 18 February 2025 and 22 April 2025 respectively. Since then a 503A pharmacy may compound either molecule only where the prescriber documents a significant difference for that specific patient, such as a strength or formulation the approved product does not offer, and the FDA has said it does not intend to act against a pharmacy filling four or fewer such prescriptions a month. On 30 April 2026 the FDA separately proposed excluding semaglutide, tirzepatide and liraglutide from the 503B bulks list used by outsourcing facilities, with comments due by 29 June 2026; that proposal concerns 503B facilities, not individual-patient 503A prescriptions. The semaglutide and tirzepatide pages explain how the physician documents that difference for each patient.

The third status is the one to understand before buying anything online. Research-use-only vials ship without a prescription from sites that state in their terms that the contents are not for human use. There is no physician, no pharmacy, no accountability for identity, purity, sterility or concentration, and no record that you took anything. The molecule may share a name with a prescription peptide; nothing else about it is comparable. Research peptides vs prescription peptides and how to tell if a peptide seller is legitimate go through the differences.

The WADA Prohibited List in force is the 2026 list, effective 1 January 2026. Growth hormone secretagogues and growth factors are prohibited at all times under section S2, and USADA states that BPC-157 is prohibited under section S0, non-approved substances, which covers any pharmacological substance with no current approval for human use. Most peptides on this page fall under one of those two sections. A tested athlete should check Global DRO or their anti-doping organization before starting anything and say so on the intake; peptides for athletes has the specifics.

The standard format is a multi-dose vial of peptide in sterile solution, drawn into a U-100 insulin syringe and injected into the fat layer of the abdomen or thigh with a short, fine needle. Directions are printed on the vial in milliliters and in syringe units, so 0.18 mL is 18 units on the barrel and nobody is calculating anything. Sites are rotated. How to inject peptides safely is the step-by-step.

Many catalog peptides also come as a pre-filled cartridge for the Pepti Pen, a reusable click-dial injector; the medication is identical to the vial and the pen removes the draw step. NAD+, Selank and Semax are available as metered nasal sprays, which suit people who will not inject; the nasal route depends on the size and chemistry of the specific molecule, which is why only some peptides are offered in it. Vial vs pen compares the injectable formats.

Because a peptide works with a signal the body already sends, when it is taken matters. Growth-hormone-axis peptides are directed at bedtime because the body's own pulse comes during deep sleep; weekly GLP-1 injections fall on the same day each week because the engineered half-life is about seven days; daily repair peptides are once daily at a consistent time. Your directions say which, and they are your physician's. Peptides ship refrigerated in insulated packaging with ice packs and stay refrigerated. A compounded preparation carries a beyond-use date rather than a manufacturer's expiry, printed on the label, and refills run every 28 days so a fresh vial arrives as the previous one finishes. How to store peptides covers the detail.

The intake asks what you are trying to change, your medical history, every medication and supplement you take, and allergies. For most peptides no formal interaction list exists, because the trials that would produce one have not been run, so the physician reviews your medication list rather than a database. Where a peptide has an approved counterpart, that label's warnings travel with the molecule.

Pregnancy and breastfeeding rule out essentially everything on this page, because the safety data is absent. A personal history of cancer is a reason to avoid peptides that promote blood-vessel growth or raise IGF-1, which includes the repair peptides and the growth-hormone axis. A personal or family history of medullary thyroid carcinoma or multiple endocrine neoplasia type 2 rules out semaglutide and tirzepatide, as their approved labels state, and a history of pancreatitis calls for caution with the same class. A physician who has read your history may decline, and being declined is refunded. Can you take peptides while pregnant and can peptides cause cancer cover the two most common questions.

Repair peptides such as BPC-157 do not routinely require labs first. Growth-hormone-axis peptides usually call for a baseline IGF-1, the GLP-1s for a metabolic baseline, and the physician may add lipids, thyroid or testosterone depending on your history. At-home blood testing covers hormone, metabolic and thyroid markers without a lab visit; do you need bloodwork before peptides lists which peptides need what.

Section 503A requires an identified individual patient and a valid prescription, so the process verifies who you are with photo identification, confirms the state you are in, and matches you to a physician licensed there. The pharmacy must be licensed to ship to your state, and each product page shows its own availability. Treatment is ongoing: one vial or cartridge is sized to about four weeks at the directed dose, refills are reviewed and sent on a 28-day rhythm one fill at a time, and the physician stays reachable for dose questions and side effects between them. Changes in dose are the physician's decision and are printed on the next label.