Peptide words
Every technical word on the cards, in plain English, and why it matters.
Definitions pending medical review
AAchondroplasia
The most common form of dwarfism. A change in one gene (FGFR3) puts too strong a brake on the growth plates, so arms and legs stay short.
Vosoritide, a copy of CNP, pushes against that brake so children grow faster; whether it raises adult height is not yet known.
On the cards: Vosoritide.
Acromegaly
A rare condition in which a pituitary tumor makes too much growth hormone in adulthood. Hands, feet and facial features slowly enlarge, and heart and blood sugar problems follow.
Octreotide, Lanreotide and Pasireotide curb the excess hormone; Pegvisomant blocks its receptor so the hormone can't act.
On the cards: Pasireotide, Pegvisomant, Lanreotide, Octreotide.
ACTH
Adrenocorticotropic hormone, made by the pituitary, a pea-sized gland under the brain. It tells the adrenal glands, on top of the kidneys, to make cortisol.
Corticotropin is ACTH itself; Cosyntropin, its first 24 amino acids, tests the adrenals; Semax uses a fragment of it with the hormone action gone.
On the cards: Semax, Corticotropin, Cosyntropin.
Actin
A protein that links up into thin filaments inside every cell. They give the cell its shape and, by growing and shrinking, let it crawl, divide and, in muscle, contract.
Thymosin Beta-4 traps loose actin to control cell movement; TB-500, its actin-grabbing piece, is sold for repair without trials in people.
On the cards: TB-500, Thymosin Beta-4.
ADNP
Activity-dependent neuroprotective protein: a protein the brain makes that helps neurons grow and keep their inner scaffolding. Faults in its gene cause a rare developmental disorder.
Davunetide is eight amino acids copied from ADNP, meant to protect neurons; in its main trial it did no better than placebo.
On the cards: Davunetide.
Adrenal glands
Two small glands sitting on top of the kidneys. They make cortisol, the stress hormone, plus adrenaline and a hormone that controls salt and blood pressure.
Corticotropin tells them to pour out cortisol; Cosyntropin pokes them as a test, to check whether they still answer.
On the cards: Corticotropin, Cosyntropin.
Albumin
The most common protein in blood plasma, made by the liver. It carries fats, hormones and drugs around the body and lasts about three weeks.
Semaglutide, Liraglutide and Somapacitan carry a fatty tail that grips albumin, and Albiglutide is fused to it: riding it makes them last.
On the cards: Tirzepatide, Semaglutide, Albiglutide, Somapacitan, Liraglutide, CJC-1295.
Alpha-MSH
Alpha-melanocyte-stimulating hormone: a 13-amino-acid hormone cut from a larger protein in the pituitary, brain and skin. It darkens skin, curbs appetite and calms inflammation.
Afamelanotide, Melanotan I and II, Setmelanotide, Bremelanotide and KPV all come from it; Melanostatine blocks its skin receptor.
On the cards: Bremelanotide, Melanotan II, PT-141, KPV, Setmelanotide, Afamelanotide, Melanostatine, Melanotan I.
Alpha4beta7 integrin
An integrin, a kind of grip protein, on some white blood cells. It latches onto gut blood vessels so those cells can leave the blood and enter the gut wall.
PN-943 is a pill meant to block it in ulcerative colitis, as the injected antibody vedolizumab does; its phase 2 results were not significant.
On the cards: PN-943.
Amino acid
The small building blocks the body strings into chains. There are about 20 common kinds; a short chain is a peptide, a long folded one is a protein.
Every card is a chain of them. Their order decides what a peptide does, and swapping a few can make it last longer, stay liquid, or block instead of activate.
On the cards: BPC-157, GHK-Cu, DSIP, Davunetide, NNZ-2591, Cosyntropin, Pramlintide, Cyclosporine, Vancomycin, AOD-9604, Dasiglucagon, Fragment 176-191, CJC-1295, IGF-1 DES and 7 more.
Amylin
A hormone the pancreas releases together with insulin after meals. It slows stomach emptying, curbs glucagon, the hormone that raises blood sugar, and tells the brain you're full.
Pramlintide copies it for diabetes; Cagrilintide, Petrelintide, Amycretin and CagriSema use it as a fullness signal for weight loss, in trials.
On the cards: Pramlintide, Amycretin, Cagrilintide, CagriSema, Petrelintide.
Analog
A lab-made version of a natural molecule, changed on purpose, often by swapping a few building blocks or adding a fatty tail, so it lasts longer or acts stronger.
Many approved drugs in the deck are analogs: Liraglutide of GLP-1, Leuprolide of GnRH, Octreotide of somatostatin, insulins tuned to act fast or slow.
On the cards: Insulin, Liraglutide, Petrelintide.
Angiotensin
A hormone made in the blood from a liver protein. Its active form, angiotensin II, squeezes blood vessels and makes the body hold salt and water, raising blood pressure.
Angiotensin II is the hormone itself, given to rescue blood pressure in shock; Dihexa is built from a fragment of it and sold for memory.
On the cards: Dihexa, Angiotensin II.
Anticoagulant
A drug that slows blood clotting, often called a blood thinner, though it does not thin the blood. It blocks steps in the chain that builds a clot.
Desirudin, the leech's own hirudin made by yeast, and Bivalirudin, inspired by it, both block thrombin, the enzyme that builds clots.
On the cards: Bivalirudin, Desirudin.
Antioxidant
A molecule that neutralizes free radicals, unstable bits of oxygen that damage DNA, fats and proteins. Cells make their own and also get some from food.
Glutathione, every cell's main antioxidant, is sold in IV drips for lighter skin on weak evidence; Carnosine is sold in creams as one.
On the cards: Carnosine, Glutathione.
AT1 receptor
Angiotensin II type 1 receptor: the main switch angiotensin II presses. On artery walls it makes them tighten, raising blood pressure; it also tells the body to keep salt.
Angiotensin II, the drug version of the hormone, presses it to narrow arteries and rescue blood pressure in shock that fluids can't fix.
On the cards: Angiotensin II.
B2 receptor
The main docking spot for bradykinin, a small swelling peptide, on blood vessel walls. When pressed, it makes vessels widen and leak fluid, so tissue swells.
Icatibant blocks it to stop the swelling attacks of hereditary angioedema; Ecallantide acts a step earlier, on the enzyme that frees bradykinin.
On the cards: Icatibant.
Barth syndrome
A rare inherited disease, almost only in males, where a fat in mitochondria, the cell's power plants, is built wrong. It weakens heart and muscles.
Elamipretide, which grips that fat, cardiolipin, got accelerated approval for muscle strength in it, based on a small open-label study.
On the cards: Elamipretide.
BDNF
Brain-derived neurotrophic factor, a protein that helps nerve cells survive, grow branches and strengthen their connections. It's key for learning and memory.
Dihexa is sold as 'ten million times more potent than BDNF'; that figure came from a press release, and its key paper was retracted in 2025.
On the cards: Dihexa.
Beta rays
Fast electrons shot out by some radioactive atoms, such as lutetium-177. In the body they travel at most about 2 mm, so they hit nearby cells and spare distant ones.
Lutetium-177 Dotatate and Lutetium-177 PSMA carry a beta-emitting atom straight to tumor cells, so the radiation damages them up close.
On the cards: Lutetium-177 Dotatate.
BNP
B-type natriuretic peptide, a hormone the heart's main pumping chambers release when stretched by too much blood. It relaxes blood vessels and makes the kidneys shed salt and water.
Nesiritide is a copy of BNP, approved for acute heart failure; a large trial found no clear benefit, and today it's hardly used.
On the cards: Nesiritide.
Bone marrow
The soft, spongy tissue inside large bones, where stem cells make all the blood cells: red cells, white cells and platelets.
Motixafortide frees stem cells from it for a transplant; Rusfertide starves it of iron so it makes fewer red cells in polycythemia vera.
On the cards: Cyclosporine, Motixafortide, Rusfertide.
Bradykinin
A nine-amino-acid peptide the body cuts loose in blood and tissues. It widens blood vessels and makes them leak fluid, which causes swelling and pain.
In hereditary angioedema too much of it causes swelling attacks; Icatibant blocks its B2 receptor and Ecallantide stops the enzyme that frees it.
On the cards: Ecallantide, Icatibant.
Calcium-sensing receptor
A sensor on the parathyroid glands, four tiny glands in the neck, that tracks blood calcium. When calcium is high it tells them to release less parathyroid hormone, which raises calcium.
Etelcalcetide mimics calcium at this sensor, so overactive parathyroid glands calm down in people on dialysis.
On the cards: Etelcalcetide.
Cardiolipin
A fat found almost only in the inner membrane of mitochondria, the cell's power plants. It holds their energy-making machinery together, like mortar between bricks.
Elamipretide grips cardiolipin; it has accelerated approval for Barth syndrome, a rare disease in which the body makes faulty cardiolipin.
On the cards: Elamipretide.
Cathelicidin
A defense protein made by skin and white blood cells. When needed, an enzyme cuts it to release a short peptide that kills bacteria and rallies immune cells.
LL-37 is the active piece cut from human cathelicidin, sold online for infections and wounds; its largest trial, in leg ulcers, found no overall benefit.
On the cards: LL-37.
CCK (cholecystokinin)
Cholecystokinin, a hormone the upper gut releases when fat and protein arrive. It squeezes the gallbladder to send out bile, prompts the pancreas to release digestive juices and adds to fullness.
Sincalide is CCK-8, its active last eight amino acids, injected during a scan to see how well the gallbladder empties.
On the cards: Sincalide.
CNP
C-type natriuretic peptide: a small peptide made in cartilage and other tissues. In the growth plates, the growing ends of children's bones, it makes bones grow longer.
Vosoritide copies CNP to push bone growth in children with achondroplasia, whose growth plates are held back by a faulty gene.
On the cards: Vosoritide.
Collagen
The body's most abundant protein: tough fibers that give skin, tendons, bone and cartilage their strength. Skin makes less of it with age and sun.
Skin peptides like Matrixyl, Collaxyl and GHK-Cu are sold to cue skin cells to make more of it; Decorinyl is meant to keep its fibers orderly.
On the cards: GHK-Cu, Carnosine, Collaxyl, Decorinyl, Matrixyl, Pal-GHK.
Complement
A set of blood proteins that helps the immune system tag germs and punch holes in them. The steps fall like dominoes; C3 and C5 are two key pieces in the chain.
Pegcetacoplan traps C3 to protect red blood cells in PNH; Zilucoplan blocks C5 to shield the nerve-muscle junction in myasthenia gravis.
On the cards: Pegcetacoplan, Zilucoplan.
Cortisol
The main stress hormone, made by the adrenal glands on top of the kidneys. It raises blood sugar, calms inflammation and follows a daily rhythm, peaking in the morning.
Corticotropin and Cosyntropin are ACTH, the signal that tells the adrenals to make cortisol; Pasireotide quiets pituitary tumors that drive too much.
On the cards: Semax, Corticotropin, Cosyntropin, Pasireotide, Ipamorelin.
CXCR4
A receptor on blood-forming stem cells and some cancer cells. It latches onto a homing signal made in the bone marrow, which holds those cells in place there.
Motixafortide blocks it to free stem cells into the blood before a myeloma transplant; Balixafortide blocked it in breast cancer but failed phase 3.
On the cards: Balixafortide, Motixafortide.
Decorin
A protein in skin and other tissues that coats collagen fibers, the skin's strength cables, and keeps them evenly sized and neatly spaced.
Decorinyl copies the spots decorin uses to grip collagen, sold to tidy collagen rather than add more; the human data is one tiny study.
On the cards: Decorinyl.
Defensins
Small germ-killing peptides made by white blood cells and by the linings of the skin, gut and airways. Their positive charge lets them punch holes in the outer membranes of bacteria.
Brilacidin, a small molecule rather than a peptide, mimics their shape and charge; it is aimed at mouth sores caused by radiation.
On the cards: Brilacidin.
DPP-4
Dipeptidyl peptidase-4: an enzyme in blood and tissues that snips the first two amino acids off GLP-1 and similar gut hormones, switching them off within minutes.
Semaglutide, Tirzepatide, Exenatide and Teduglutide are built so DPP-4 cannot cut them, a big part of why they last.
On the cards: Tirzepatide, Semaglutide, Dulaglutide, Exenatide, Teduglutide.
EGF
Epidermal growth factor, a 53-amino-acid protein that tells skin and gut lining cells to multiply, as happens when a wound closes.
Oligopeptide-1 is human EGF made in microbes or plants and sold in serums; it is far too big to get through intact skin easily.
On the cards: Oligopeptide-1.
Elastin
The stretchy protein that lets skin, arteries and lungs spring back after being pulled. The body makes most of it early in life, and it slowly wears out with age and sun.
Biopeptide EL is VGVAPG, a sequence that repeats in elastin, sold to restore firmness; no published trial in people backs that yet.
On the cards: Biopeptide EL.
Endometriosis
A condition in which tissue like the womb's lining grows outside the womb, often on the ovaries or pelvis. It feeds on estrogen and can cause pain and infertility.
Nafarelin, Leuprolide and Goserelin treat it by shutting down the pituitary's signals, so estrogen falls and the tissue quiets.
On the cards: Goserelin, Leuprolide, Nafarelin.
Enkephalin
The body's own small opioids, five amino acids long. They press opioid receptors, the same family morphine acts on, damping pain signals passed between nerves.
Leuphasyl is Leu-enkephalin with one mirror-image amino acid so it lasts, sold in creams to relax expression lines.
On the cards: Leuphasyl.
Enzyme
A protein that speeds up one chemical job in the body, such as cutting another molecule or building one. Each enzyme is picky about what it works on.
Some peptides block an enzyme, like Bivalirudin with thrombin; others are built so enzymes such as DPP-4 cannot cut them, so they last longer.
On the cards: Epitalon, Bivalirudin, 5-Amino-1MQ, CJC-1295, Ecallantide.
Exendin-4
A peptide from the venom of the Gila monster, a desert lizard. It acts like human GLP-1, the gut's fullness hormone, but lasts hours instead of minutes.
Exenatide is a synthetic copy; Lixisenatide is a tweaked version and Efpeglenatide joins it to an antibody piece. All lower blood sugar.
On the cards: Efpeglenatide, Exenatide, Lixisenatide.
Fibroblasts
The builder cells of skin and other connective tissue. They make collagen and elastin, the proteins that give skin its strength and stretch, and help close wounds.
GHK-Cu, Matrixyl and Collaxyl are sold to cue them to make more collagen, an effect shown mainly in lab dishes.
Fragile X
The most common inherited cause of intellectual disability, from a silenced gene on the X chromosome. It often brings anxiety and autism-like traits, more severe in boys.
On the IV Trofinetide card, the molecule was later taken by mouth for fragile X; a 28-day trial in 72 teen and adult males gave only a preliminary signal.
On the cards: IV Trofinetide.
Free radicals
Unstable, highly reactive molecules, made as cells burn fuel or by sunlight, that damage DNA, fats and proteins by stealing electrons from them.
Glutathione, every cell's main antioxidant, mops them up; Carnosine is sold in creams as a shield against them.
On the cards: Glutathione.
GABA
Gamma-aminobutyric acid, the brain's main brake. Nerve cells release it to quiet their neighbors, and anti-anxiety drugs like diazepam boost its effect.
Selank is sold for anxiety and thought to work through it, but the evidence is rat gene studies and small trials without placebo.
On the cards: Selank.
GHK
Glycine, histidine and lysine: a three-amino-acid peptide found naturally in human blood, first isolated in 1973. It grabs copper atoms tightly.
GHK-Cu is GHK holding its copper, and Pal-GHK swaps the copper for a fatty tail; both are sold in skin serums as collagen signals.
Ghrelin
The hunger hormone, made mostly by the stomach when it's empty. It makes you want to eat and tells the pituitary, a gland under the brain, to release growth hormone.
GHRP-2, GHRP-6, Hexarelin, Ipamorelin and MK-677 mimic it at its receptor to trigger growth hormone; GHRP-6 was made before ghrelin was found.
On the cards: GHRP-2, GHRP-6, Hexarelin, Ipamorelin, MK-677.
GHRH
Growth hormone-releasing hormone: a signal from the base of the brain telling the pituitary, a pea-sized gland below it, to release growth hormone in pulses.
Tesamorelin copies all 44 of its amino acids; Sermorelin and CJC-1295 copy its first 29. All aim to make the pituitary release its own growth hormone.
On the cards: Compounded Tesamorelin, Tesamorelin, CJC-1295, Sermorelin.
GIP
Short for glucose-dependent insulinotropic polypeptide, a hormone the gut releases after meals. It tells the pancreas to release more insulin while blood sugar is high.
Tirzepatide is built on GIP and switches on both the GIP and GLP-1 receptors; Retatrutide hits those two plus the glucagon receptor.
On the cards: Tirzepatide, Retatrutide.
GLP-1
Glucagon-like peptide-1, a hormone the gut releases after meals. It helps the pancreas release insulin when sugar is high, slows the stomach and signals fullness.
Natural GLP-1 lasts minutes; Semaglutide, Liraglutide and Dulaglutide copy it to last a day or a week, and Tirzepatide and Retatrutide add other hormones.
On the cards: Tirzepatide, Semaglutide, Retatrutide, Albiglutide, Dulaglutide, Efpeglenatide, Exenatide, Lixisenatide, Amycretin, CagriSema, Glucagon, Liraglutide, Mazdutide, Pemvidutide and 2 more.
GLP-2
Glucagon-like peptide 2, a hormone the lower gut releases after meals. It makes the gut lining grow, with taller absorbing folds, so more food and water get through.
Teduglutide copies it to help a short bowel absorb more and need less IV feeding; Apraglutide and Glepaglutide are longer-lasting copies in trials.
On the cards: Apraglutide, Glepaglutide, Glucagon, Teduglutide.
Glucagon
A pancreas hormone that does the opposite of insulin: when blood sugar falls, it tells the liver to release its stored sugar. It also pushes the liver to burn fat.
Glucagon and Dasiglucagon rescue severe sugar crashes; Survodutide, Pemvidutide, Mazdutide and Retatrutide switch on its receptor, aiming to burn liver fat.
On the cards: Retatrutide, Dasiglucagon, Mazdutide, Pemvidutide, Survodutide.
Glycation
Sugar in the body sticking to proteins on its own, a bit like food browning in an oven. In skin it stiffens collagen, the protein that keeps skin firm.
Carnosine is sold in creams to shield collagen from it; the evidence is lab-grown human skin, in a study by the ingredient's seller.
On the cards: Carnosine.
Glycopeptide
A peptide with sugar molecules attached. In medicine the word usually means a family of antibiotics, first found in soil bacteria, that stop germs from building their outer wall.
Vancomycin is the classic glycopeptide; Dalbavancin and its cousins add a fatty tail so they last longer and anchor to bacteria.
On the cards: Vancomycin, Dalbavancin & Co..
GnRH
Gonadotropin-releasing hormone, sent from the brain in pulses to the pituitary, a pea-sized gland below it, which then releases the hormones that run testes and ovaries.
Pulsed, it switches sex hormones on; nonstop, as with Leuprolide or Goserelin, it shuts them off. Cetrorelix and Degarelix block its receptor outright.
On the cards: Kisspeptin-10, Cetrorelix, Degarelix, Ganirelix, Gonadorelin, Goserelin, Histrelin, Leuprolide, Nafarelin, Triptorelin.
GP IIb/IIIa
A receptor on platelets, tiny cell fragments that start clots. Once switched on, it grabs a blood protein called fibrinogen that links platelets into a clump.
Eptifibatide, modeled on rattlesnake venom, blocks it so platelets clump less during heart attacks and artery stenting.
On the cards: Eptifibatide.
gp41
A protein on HIV's outer coat. When the virus touches a cell, gp41 folds up like a spring, pulling virus and cell together so their outer layers fuse and the virus gets in.
Enfuvirtide is a piece copied from gp41 that sticks to it and blocks the fold, so HIV can't get into the cell.
On the cards: Enfuvirtide.
Gram-negative bacteria
Bacteria wrapped in an extra outer membrane that keeps many antibiotics out. The name comes from a lab stain they don't hold. E. coli and Pseudomonas are examples.
Polymyxin B and Colistin pierce that outer membrane and are kept as a last resort for gram-negative infections that resist other drugs.
On the cards: Polymyxin B & Colistin.
Growth hormone
A hormone the pituitary, a gland under the brain, releases in pulses, mostly in sleep. It makes children grow and has the liver make IGF-1, a growth signal; in adults it shapes fat, muscle and bone.
Somatropin replaces it; Tesamorelin and the ghrelin mimics make the pituitary release more; Octreotide and Pegvisomant hold back an excess of it.
On the cards: Compounded Tesamorelin, Mecasermin, Pasireotide, Pegvisomant, Somapacitan, Somatropin, AOD-9604, Fragment 176-191, Lanreotide, Octreotide, Tesamorelin, CJC-1295, GHRP-2, GHRP-6 and 6 more.
Growth plates
Discs of cartilage near the ends of children's long bones where new bone is added, making them longer. They close after puberty, and growth in height stops.
Vosoritide acts on NPR-B in them to speed growth in achondroplasia, so it is given only while they are still open.
On the cards: Vosoritide.
Guanylate cyclase-C
A receptor on the cells lining the gut. When the gut's own hormones press it, the lining pours salt and water into the bowel, which softens stool.
Linaclotide presses it, like the E. coli toxin behind traveler's diarrhea, to ease constipation, and it acts in the gut without reaching the blood.
On the cards: Linaclotide.
Hepcidin
A hormone made by the liver that controls iron. It shuts the door iron uses to leave the gut and the body's stores, so less iron reaches the blood.
Rusfertide mimics it to keep iron scarce, so the bone marrow makes fewer red blood cells in polycythemia vera.
On the cards: Rusfertide.
Hereditary angioedema
An inherited disorder, usually from a missing or faulty brake protein, that lets bradykinin, a molecule that makes vessels leak, build up. It causes sudden swelling of the skin, gut or throat.
Icatibant blocks bradykinin's receptor and Ecallantide blocks the enzyme that frees it; both are used to treat attacks as they happen.
On the cards: Ecallantide, Icatibant.
Hormone
A chemical message one part of the body releases into the blood to give orders elsewhere, like insulin telling muscle to take up sugar. Many hormones are peptides.
Many cards copy a hormone and tweak it to last, like Semaglutide from GLP-1; others block one, like Cetrorelix at the GnRH receptor.
On the cards: Teriparatide, Kisspeptin-10, Semaglutide, Melanotan II, Dihexa, Semax, Compounded Tesamorelin, Exenatide, Mecasermin, Pasireotide, Pegvisomant, Pramlintide, Secretin, Somapacitan and 35 more.
Hypoparathyroidism
When the parathyroid glands in the neck make too little parathyroid hormone, often after neck surgery. Blood calcium falls, causing tingling and muscle cramps.
Palopegteriparatide replaces the missing hormone with a slow, all-day release; Parathyroid Hormone did the same until it was withdrawn.
On the cards: Palopegteriparatide, Parathyroid Hormone.
Hypothalamus
A small area at the base of the brain that runs hunger, thirst, body heat, sleep and sex drive, and gives orders to the pituitary, the hormone gland below it.
Many cards copy its signals, like Tesamorelin (GHRH) and Leuprolide (GnRH); Setmelanotide and Bremelanotide act on its MC4 receptors.
On the cards: Bremelanotide, Kisspeptin-10, PT-141, Compounded Tesamorelin, Setmelanotide, CJC-1295, Sermorelin.
IGF-1
Insulin-like growth factor 1: the growth signal the liver releases when growth hormone reaches it. It tells bone, muscle and other tissues to grow.
Mecasermin is IGF-1 itself and Somatropin raises it; IGF-1 LR3 and IGF-1 DES are altered versions sold online for muscle.
On the cards: NNZ-2591, Trofinetide, Mecasermin, Somatropin, IGF-1 DES, IGF-1 LR3, MGF, MK-677.
Immune system
The body's defense network: white blood cells, antibodies and messenger molecules that find and kill germs and damaged cells, and cause inflammation.
Many cards work on it: germ-killers like LL-37, Thymosin Alpha-1 meant to boost it, Cyclosporine to hold it back after transplants.
On the cards: Thymulin, Brilacidin.
Insulin
The pancreas's hormone for storing fuel: after a meal it tells muscle, fat and liver to pull sugar (glucose) out of the blood. In type 1 diabetes the body makes little or none.
Insulin analogs replace it; gut-hormone copies like Exenatide and Tirzepatide make the pancreas release more of it, but only when blood sugar is high.
On the cards: Insulin, Tirzepatide, Albiglutide, Dulaglutide, Exenatide, Lixisenatide, Pramlintide, Cagrilintide, Glucagon.
IVF
In vitro fertilization: eggs are collected from the ovaries, fertilized with sperm in a lab dish, and the resulting embryo is placed in the uterus.
Cetrorelix and Ganirelix block the GnRH receptor so the eggs are not released before doctors can collect them.
On the cards: Cetrorelix, Ganirelix.
Kappa opioid receptor
One of three main switches for the body's opioids, the natural painkillers morphine copies. Unlike mu, morphine's switch, kappa can calm itch and pain without the euphoria that drives addiction.
Difelikefalin switches it on and is built to stay out of the brain; it treats itch in people on dialysis, though the FDA says the exact reason is unclear.
On the cards: Difelikefalin.
Lactoferricin
A germ-killing piece freed when digestion cuts lactoferrin, an iron-binding protein in milk. Its positive charge lets it rip open the outer skin of microbes.
LTX-315 was designed from cow lactoferricin; injected into tumors, it bursts cancer cells and is meant to rouse the immune system against them.
On the cards: LTX-315.
LDL cholesterol
Cholesterol riding in LDL particles, tiny fat-and-protein carriers in the blood. Too much builds up in artery walls, hence the name bad cholesterol.
Enlicitide blocks PCSK9 so the liver keeps more LDL receptors and clears more of it; whether that prevents heart attacks is still being tested.
On the cards: Enlicitide.
LDL receptor
A catcher on liver cells that grabs LDL, the 'bad cholesterol' particles, from the blood and pulls them inside to be broken down. More receptors mean lower LDL.
Enlicitide blocks PCSK9, the protein that destroys these receptors, so more of them stay on the liver and blood LDL falls.
On the cards: Enlicitide.
LH
Luteinizing hormone, made by the pituitary, a gland under the brain. In women a sudden surge of it releases an egg; in men it tells the testes to make testosterone.
Cetrorelix and Ganirelix hold back its surge so eggs stay put until IVF retrieval; hCG mimics it to trigger ovulation or testosterone.
On the cards: Cetrorelix, Ganirelix, hCG.
Lipopeptide
A peptide with a fatty tail attached. The tail lets it stick to or slip into cell membranes, the oily outer skin of cells.
Daptomycin is a lipopeptide antibiotic that punctures bacterial membranes; Polymyxin B and Colistin also use a fatty tail to pierce them.
On the cards: Daptomycin.
LptD
A protein in the outer coat of some bacteria that ferries fat-and-sugar molecules into that coat. Without it, the bacterium cannot finish its protective shell.
Murepavadin locks onto the Pseudomonas version only, sparing other bacteria; its main trial was stopped over kidney damage.
On the cards: Murepavadin.
MASH
Metabolic dysfunction-associated steatohepatitis: fat builds up in the liver and inflames it, often with obesity or diabetes. Over years it can scar the liver.
Semaglutide is approved for it in the US when the liver is scarring; Pemvidutide, still in trials, is built for it.
On the cards: Semaglutide, Pemvidutide.
MC1R
Melanocortin 1 receptor: a switch on the skin's pigment cells. When alpha-MSH presses it, they make dark pigment that shields skin from sun. Weak versions are common in redheads.
Afamelanotide and Melanotan I switch it on to tan skin from within; Melanostatine is sold to block it and fade dark spots.
On the cards: Afamelanotide, Melanostatine, Melanotan I.
MC4 receptor
A switch on brain cells, mostly in the hypothalamus. When the body's melanocortin hormones press it, appetite drops and sexual desire rises.
Setmelanotide presses it to curb hunger in rare genetic obesity; Bremelanotide presses it to raise low desire.
On the cards: Bremelanotide, Setmelanotide.
Melanocortin receptors
Five related switches on cells, pressed by melanocortin hormones such as alpha-MSH. MC1 on pigment cells darkens skin; MC4 in the brain curbs hunger and raises desire.
Melanotan II presses several, so it tans and causes erections; Afamelanotide aims at MC1, Setmelanotide and Bremelanotide at MC4.
On the cards: Melanotan II, PT-141.
Mitochondria
Tiny compartments inside cells that turn food and oxygen into usable energy. They carry their own small set of DNA, passed down from the mother.
Elamipretide grips their inner membrane to treat Barth syndrome; MOTS-c and Humanin are peptides coded by their DNA, sold for fat loss and longevity.
On the cards: Humanin, MOTS-c, Elamipretide.
MRSA
Methicillin-resistant Staphylococcus aureus: a strain of the common staph bacterium that shrugs off penicillin-type antibiotics. It causes hard-to-treat skin and blood infections.
Vancomycin, Daptomycin and Dalbavancin and its cousins are peptide antibiotics used against it, mostly in skin and blood infections.
On the cards: Vancomycin, Dalbavancin & Co., Daptomycin.
Myasthenia gravis
An autoimmune disease: the immune system attacks the junction where nerves tell muscles to move, so muscles tire fast. Drooping eyelids and double vision are common.
Zilucoplan blocks complement C5, part of the immune attack that damages the nerve-muscle junction, in adults with the antibody form.
On the cards: Zilucoplan.
Myometrium
The thick muscle wall of the uterus. It squeezes in waves during labor and clamps down after birth to close off bleeding vessels.
Oxytocin makes it contract, to start or strengthen labor and to prevent heavy bleeding after childbirth.
On the cards: Oxytocin.
Myostatin
A signal muscle makes to limit its own growth. Animals and rare people born without working myostatin have unusually large muscles.
Follistatin-344 is a protein that traps myostatin, sold in vials to build muscle; only gene-therapy versions have been tested in people.
On the cards: Follistatin-344.
Neuroendocrine tumors
Tumors of hormone-making cells, most often in the gut, pancreas or lungs. Many grow slowly, and most carry receptors for somatostatin, the body's hormone brake.
Octreotide and Lanreotide slow some or calm their symptoms; Gallium-68 Dotatate finds them on a PET scan and Lutetium-177 Dotatate irradiates them.
On the cards: Lutetium-177 Dotatate, Gallium-68 Dotatate, Lanreotide, Octreotide.
Neurons
Nerve cells: the cells of the brain and nerves that carry signals as electrical pulses and pass them to the next cell with chemical messengers.
Davunetide, Cerebrolysin and Dihexa are meant to protect or grow them; Kisspeptin-10 wakes the GnRH neurons that run the sex hormones.
On the cards: Humanin, Kisspeptin-10, Cerebrolysin, Davunetide, Dihexa, Argireline.
NNMT
Nicotinamide N-methyltransferase: an enzyme in fat cells and the liver that uses up a form of vitamin B3, which cells also need to make energy.
5-Amino-1MQ, a small molecule sold online to burn fat, blocks it; it slimmed obese mice but has never been tested in people.
On the cards: 5-Amino-1MQ.
NPR-B
Natriuretic peptide receptor B: a switch on cartilage cells in the growth plates, the growing ends of children's bones. When CNP presses it, bones grow longer.
Vosoritide presses it, mimicking CNP, to speed growth in children with achondroplasia while their growth plates are still open.
On the cards: Vosoritide.
Osteoblasts
The bone-building cells. They lay down fresh collagen and mineral to form new bone, while their partners, osteoclasts, dissolve old bone.
Teriparatide and Abaloparatide, given as daily pulses, spur osteoblasts through the PTH1 receptor to build new bone in osteoporosis.
On the cards: Teriparatide, Abaloparatide.
Osteoclasts
Bone cells that dissolve old bone, releasing its calcium into the blood. They work in balance with osteoblasts, the cells that lay down new bone.
Salmon Calcitonin calms them, lowering blood calcium; it is used in Paget's disease and for high blood calcium.
On the cards: Salmon Calcitonin.
Oxyntomodulin
A gut hormone released after meals, cut from the same parent protein as glucagon and GLP-1. It switches on both of their receptors, curbing appetite.
Mazdutide copies it, hitting GLP-1 and glucagon receptors in one weekly shot; Survodutide and Pemvidutide follow the same two-receptor idea.
On the cards: Mazdutide.
Paget's disease
A bone disease in which bone is broken down and rebuilt too fast and in a messy way, leaving bones enlarged, weak or misshapen, often in the pelvis, spine or skull.
Salmon Calcitonin is approved for it: it calms osteoclasts, the cells that dissolve bone, slowing the runaway turnover.
On the cards: Salmon Calcitonin.
Parathyroid glands
Four rice-grain-sized glands in the neck, behind the thyroid. They sense blood calcium and release parathyroid hormone when it drops, to bring it back up.
Teriparatide and Palopegteriparatide carry their hormone's active end, for bone or failed glands; Etelcalcetide calms overactive glands.
On the cards: Etelcalcetide, Parathyroid Hormone.
Parathyroid hormone (PTH)
Made by four tiny glands in the neck. When blood calcium drops, it pulls calcium from bone, keeps it from leaving in urine and, via vitamin D, gets the gut to absorb more.
Teriparatide, its active end in daily pulses, builds bone; Palopegteriparatide replaces it when the glands fail; Etelcalcetide lowers it.
On the cards: Teriparatide, Abaloparatide, Etelcalcetide, Palopegteriparatide, Parathyroid Hormone.
PCSK9
A liver protein that marks the liver's LDL receptors, the docks that pull 'bad' cholesterol out of the blood, for destruction. Less PCSK9 means more docks and lower LDL.
Enlicitide is a daily pill that blocks it, lowering LDL cholesterol; whether that prevents heart attacks is still being tested.
On the cards: Enlicitide.
PEG
Polyethylene glycol, a long, flexible, water-loving chain molecule. Tied to a drug, it makes it too bulky for the kidneys to filter out, so it lasts longer.
Palopegteriparatide, Pegvisomant and Pegcetacoplan carry PEG to last; in Palopegteriparatide it frees the hormone slowly all day.
On the cards: Pegvisomant, Pegcetacoplan, MGF, Palopegteriparatide, Zilucoplan.
Peptide
A short chain of amino acids, the building blocks of protein, linked end to end. For the FDA, up to 40 amino acids is a peptide; longer chains count as proteins.
Nearly every card is one: a body signal copied, trimmed or armored to last. A few, like MK-677 and 5-Amino-1MQ, are not peptides at all.
On the cards: Epitalon, Thymosin Alpha-1, Humanin, Cerebrolysin, Selank, Aviptadil, Nangibotide, Echinocandins, 5-Amino-1MQ, Brilacidin, MGF, MK-677, Vosoritide, Zilucoplan and 3 more.
PET scan
Positron emission tomography: a scan that tracks a weakly radioactive tracer injected into the body, showing where it gathers, such as in tumors.
Gallium-68 Dotatate makes tumors with somatostatin receptors glow on PET, showing who can be treated with Lutetium-177 Dotatate.
On the cards: Gallium-68 Dotatate, Lutetium-177 PSMA.
Pigment cells (melanocytes)
Cells at the base of the skin's outer layer that make melanin, the brown pigment, and hand it to nearby skin cells as a shield against sunlight.
Afamelanotide and Melanotan I make them produce more pigment; Melanostatine and Glutathione are sold to lighten skin.
On the cards: Afamelanotide, Melanostatine, Melanotan I.
Pituitary
A pea-sized gland at the base of the brain that releases hormones for growth, sex, stress, water balance and the thyroid. The hypothalamus, just above it, tells it what to do.
A hub of the deck: Tesamorelin and the ghrelin mimics make it release growth hormone, while Leuprolide and Cetrorelix shut down its sex-hormone signals.
On the cards: Compounded Tesamorelin, Corticotropin, Pasireotide, Somatropin, Tesamorelin, Cetrorelix, Degarelix, Ganirelix, Gonadorelin, Goserelin, hCG, Histrelin, Leuprolide, Nafarelin and 5 more.
Plasma kallikrein
A blood enzyme, a protein that cuts other proteins, that frees bradykinin, a small peptide that makes blood vessels leak fluid. A brake protein, C1 inhibitor, normally keeps it in check.
In hereditary angioedema that brake is often missing, so it runs unchecked; Ecallantide blocks it to treat swelling attacks.
On the cards: Ecallantide.
Platelets
Tiny cell fragments in the blood that plug leaks. At a wound they turn sticky, clump and start a clot; inside a narrowed artery, that clot can cause a heart attack.
Eptifibatide blocks GP IIb/IIIa, the receptor they use to clump together, during heart attacks and artery stenting.
On the cards: Nangibotide, Eptifibatide.
PNH
Paroxysmal nocturnal hemoglobinuria: a rare blood disease in which red blood cells lack their protective coat, so the complement system destroys them. Urine can turn dark.
Pegcetacoplan traps C3, an early step of the complement attack, so fewer red blood cells are destroyed and fewer transfusions are needed.
On the cards: Pegcetacoplan.
Polycythemia vera
A slow blood cancer of the bone marrow that makes too many red blood cells. The thick blood raises the risk of clots; regular blood draws are the classic treatment.
Rusfertide mimics hepcidin to starve the marrow of iron, so fewer red cells form and patients need fewer blood draws.
On the cards: Rusfertide.
Procollagen
The longer starting form of collagen, the protein that keeps skin firm. Cells make it first, then trim off its ends to build collagen fibers.
Matrixyl is KTTKS, a five-amino-acid piece of procollagen on a fatty tail, sold to cue skin cells to make more collagen.
On the cards: Matrixyl.
Pseudomonas
A common water and soil bacterium, often resistant to many antibiotics, that causes lung, blood and wound infections in hospital patients and people with weak defenses.
Murepavadin was built to hit only Pseudomonas, via its LptD coat protein; Polymyxin B & Colistin are last-resort drugs that also kill it.
On the cards: Murepavadin, Polymyxin B & Colistin.
PSMA
Prostate-specific membrane antigen: a protein on the surface of prostate cells. Most prostate cancer cells carry far more of it, so it works as a tag to find them.
Lutetium-177 PSMA latches onto it to deliver radiation to prostate cancer cells; a PET scan first checks that the tumor has it.
On the cards: Lutetium-177 PSMA.
PTH1 receptor
The receptor for parathyroid hormone and its sister PTHrP, on bone and kidney cells. Brief daily pulses build bone; constant pressure pulls calcium out of it.
Teriparatide and Abaloparatide press it in daily pulses to build bone in osteoporosis; Palopegteriparatide presses it steadily to raise calcium.
On the cards: Abaloparatide.
Receptor
A protein on a cell's surface, or inside it, shaped to catch one kind of signal molecule, like a lock for a key. When the right molecule docks, the cell changes what it does.
Most peptides in the deck work through one: they press it like a natural hormone (Semaglutide, Setmelanotide) or sit in it to block it (Cetrorelix, Icatibant).
On the cards: Insulin, Bremelanotide, Tirzepatide, Vasopressin, Lutetium-177 Dotatate, Melanotan II, Retatrutide, Gallium-68 Dotatate, PT-141, Pasireotide, Pegvisomant, Nangibotide, Angiotensin II, Balixafortide and 21 more.
Red blood cells
The disc-shaped cells that make blood red. Packed with hemoglobin, an iron-rich protein, they carry oxygen from the lungs to every tissue.
Pegcetacoplan shields them from immune attack in PNH; Rusfertide limits iron so the marrow makes fewer of them in polycythemia vera.
On the cards: Pegcetacoplan, Rusfertide.
Rett syndrome
A rare genetic brain disorder, almost always in girls. After 6 to 18 months of normal development, children lose speech and purposeful use of their hands.
Trofinetide, a tweaked piece of IGF-1, is approved for it; in its trial, symptoms eased a little more than with placebo.
On the cards: Trofinetide.
Septic shock
The most severe stage of sepsis, when the body's response to an infection injures its own organs and blood pressure falls so low that drugs must hold it up.
Selepressin and Nangibotide were tried in it, one to raise blood pressure, one to calm inflammation; neither improved outcomes in trials.
On the cards: Nangibotide, Angiotensin II, Selepressin.
Small molecule
A drug built from a few dozen atoms, far smaller than a peptide and not a chain of amino acids, the building blocks of proteins. Many can be taken as pills.
MK-677, 5-Amino-1MQ and Brilacidin are small molecules, not peptides; they're in the deck because they copy a peptide's job or are sold alongside them.
On the cards: 5-Amino-1MQ, MK-677.
SNAP-25
A protein in nerve endings that helps them release their chemical message to muscle. Botulinum toxin works by cutting it, so the muscle relaxes.
Argireline and SNAP-8 copy one of its ends, sold in creams to relax expression lines; Argireline barely gets through the skin in tests.
On the cards: Argireline, SNAP-8.
Somatostatin
A hormone made in the brain, gut and pancreas that acts as a brake on other hormones, including growth hormone, insulin and many gut hormones. It lasts only minutes.
Octreotide, Lanreotide and Pasireotide are longer-lasting copies; Lutetium-177 and Gallium-68 Dotatate use its receptors to treat or find gut tumors.
On the cards: Lutetium-177 Dotatate, Gallium-68 Dotatate, Pasireotide, Lanreotide, Octreotide, Hexarelin.
Stem cells
Unspecialized cells that can copy themselves and mature into other cell types. The blood-forming ones in the bone marrow make all the blood's cells, red and white.
Motixafortide frees blood stem cells from the marrow by blocking CXCR4, their anchor, so they can be collected for a myeloma transplant.
On the cards: Motixafortide.
Synapses
The tiny gaps where one nerve cell passes a signal to the next, using chemical messengers. Making, strengthening and pruning them is how the brain learns and remembers.
Dihexa is sold to grow them, a claim based on rat neurons in a dish; the paper on how it works was retracted in 2025.
On the cards: Dihexa, Trofinetide.
T cells
White blood cells that mature in the thymus, a gland behind the breastbone. Some kill infected or cancer cells; others direct the rest of the immune response.
Cyclosporine reins them in so a transplanted organ isn't rejected; Thymosin Alpha-1 is meant to boost them, but a large sepsis trial showed no benefit.
On the cards: Thymosin Alpha-1, Cyclosporine.
Telomerase
An enzyme that rebuilds telomeres, the protective tips of chromosomes that wear down each time a cell divides. Stem cells and most cancer cells keep it on.
Epitalon is sold for longevity, meant to switch it on; in cells it did, cancer cells included, but normal mice did not live longer.
On the cards: Epitalon.
Telomeres
Protective caps of repeated DNA at the ends of each chromosome, the packages that hold your genes. They shorten a little as cells divide, and very short ones make cells stop dividing.
Epitalon is sold to lengthen them; it switched on telomerase in cells, but mice given it did not live longer.
On the cards: Epitalon.
Thrombin
The key enzyme of blood clotting. It cuts fibrinogen, a blood protein, into fibrin strands that knit the clot together, and it also switches on platelets.
Bivalirudin and Desirudin, both based on leech hirudin, block it directly to prevent clots during heart procedures or after hip surgery.
On the cards: Bivalirudin, Desirudin.
Thymus
A gland behind the breastbone where T cells, the immune system's trained fighters, learn to tell germs from the body's own tissue. It shrinks after puberty.
Thymosin Alpha-1 and Thymulin are thymus peptides meant to strengthen immune defenses; neither is FDA approved.
On the cards: Thymosin Alpha-1, Thymulin.
Tight junctions
Seals that stitch neighboring cells together in a lining, such as the gut wall, controlling what slips between them. When they loosen, the lining gets leakier.
Larazotide was designed to tighten them in celiac disease, where gluten pries them open; trials found no change in gut leakiness.
On the cards: Larazotide.
TREM-1
Triggering receptor expressed on myeloid cells 1: a switch on some white blood cells that turns up inflammation, like an amplifier, during serious infections.
Nangibotide is a decoy meant to hold it back in septic shock; in its largest trial it did not reduce organ failure.
On the cards: Nangibotide.
Tuftsin
A four-amino-acid piece cut from an antibody, one of the immune system's Y-shaped defense proteins. Once freed, it wakes up the white blood cells that swallow germs.
Selank is tuftsin plus a short tail, sold as nasal drops for anxiety; the evidence comes mostly from rats and one small study without placebo.
On the cards: Selank.
Uroguanylin
A hormone made by the gut lining. It switches on a receptor in the gut wall that makes the bowel release salt and water, which softens stool.
Plecanatide is uroguanylin with one change, working like it in the small intestine to pull in water and ease constipation.
On the cards: Linaclotide, Plecanatide.
V1 and V2 receptors
Two docking sites for vasopressin, the body's water-keeping hormone. V1 sits on blood vessel walls and tightens them; V2 sits in the kidneys and makes them hold on to water.
Vasopressin hits both; Selepressin was tuned to V1 alone to hold blood pressure, and Desmopressin to V2 alone to hold water without raising pressure.
On the cards: Vasopressin, Desmopressin, Selepressin.
Vasopressin
A hormone made in the brain and released by the pituitary when the body runs short of water. It makes the kidneys hold water and, at higher levels, tightens blood vessels.
Vasopressin itself is a drug for shock; Desmopressin, Terlipressin and Selepressin are tuned copies, each aimed at water, gut blood flow or blood pressure.
On the cards: Oxytocin, Vasopressin, Desmopressin, Selepressin, Terlipressin.
Villi
Tiny finger-like folds lining the small intestine, packed side by side like velvet. They multiply the surface that absorbs food and water.
Teduglutide copies GLP-2 to make them grow taller, so a short bowel absorbs more; Glepaglutide and Apraglutide aim to do the same.
On the cards: Teduglutide.
VIP
Vasoactive intestinal peptide, a messenger released by nerves in the gut, lungs and brain. It relaxes the muscle in the walls of blood vessels and airways, widening them.
Aviptadil is an exact copy, tried in severe COVID in the hope of protecting the lungs; in a large trial it did no better than placebo.
On the cards: Aviptadil.
Visceral fat
The deep belly fat packed around the organs inside the abdomen, not the fat you can pinch. Too much of it is tied to diabetes and heart disease.
Tesamorelin raises the body's own growth hormone to shrink it in people with HIV; it comes back after stopping.
On the cards: Tesamorelin.
White blood cells
The immune system's mobile cells. They travel in the blood and slip into tissues to fight germs and clear damage, and they drive inflammation.
PN-943 is meant to block the grip they use to enter the gut wall; LL-37 is a germ-killer some of them make, sold for infections and wounds.