168 terms

What the words mean.

Health writing hides a great deal behind its vocabulary. Every technical term on this site is defined here, and again wherever it appears: hover it on a desktop, tap it on a phone.

168 terms

Peptides & regulation

The compounds themselves, how they are given, and the rules that govern who can sell them.

503A: The section of federal law covering pharmacies that compound for individual patients. The "503A bulks list" names the raw substances they are allowed to compound from.
amino acid: The small molecules your body links together to build protein. Chain a few dozen and you have a peptide; chain hundreds and you have a protein.
bioavailability: How much of what you take actually reaches your bloodstream. Swallowing something with low bioavailability can mean most of the dose never arrives.
BPC-157 Body Protection Compound 157: A peptide fragment originally found in stomach fluid. Animal studies show striking tendon, ligament, and gut healing effects. Human trials for those uses are still rare.
CJC-1295: A synthetic version of the signal that tells the pituitary to release growth hormone. Sold in two forms, with and without DAC, which changes how long it lasts.
compounding: A licensed pharmacy mixing a drug to order for a specific patient, rather than dispensing a mass-manufactured product. What a pharmacy may compound from is set by federal lists.
DAC Drug Affinity Complex: An add-on that makes a peptide bind to albumin in the blood so it clears more slowly. A DAC version lasts days instead of hours, which changes the dosing schedule entirely.
Epitalon: A four-amino-acid peptide studied in small Russian trials for aging and sleep-wake rhythm. The trials are old, small, and have not been repeated independently.
FDA Food and Drug Administration: The US agency that decides which drugs may be sold, and on what terms. Its approval of a drug is specific to a use, a dose, and a manufacturer.
GH growth hormone: A hormone from the pituitary gland that drives growth in childhood and helps maintain muscle, bone, and metabolism in adults.
GHK-Cu copper tripeptide-1: A copper-carrying peptide that occurs naturally in human plasma. Used in skincare for wound healing and collagen remodeling, where the topical evidence is the strongest part of its case.
GHRH growth hormone releasing hormone: The natural signal from the brain that tells the pituitary gland to release growth hormone. Several research peptides are built to imitate it.
GIP glucose-dependent insulinotropic polypeptide: A second gut hormone that works alongside GLP-1 on insulin and appetite. Tirzepatide hits both, which is the main difference from semaglutide.
GLP-1 glucagon-like peptide-1: A gut hormone released after eating that raises insulin, slows stomach emptying, and reduces appetite. Semaglutide and tirzepatide are drugs built to imitate it.
half-life: How long it takes the body to clear half of a dose. It sets how often something has to be taken: a two-hour half-life and a five-day half-life are different products even at the same dose.
HSDD hypoactive sexual desire disorder: Persistently low sexual desire that causes distress. A recognised diagnosis, which matters because it is what some drugs are actually approved to treat.
hydrolyzed: Broken into smaller pieces with water and enzymes before you buy it. Hydrolyzed collagen is collagen already cut into fragments short enough to survive digestion.
IGF-1 insulin-like growth factor 1: The hormone that carries out most of growth hormone's effects on tissue. Blood levels of it are how clinicians check whether growth hormone is doing anything.
intramuscular: Injected into muscle. Absorbs faster than under the skin and needs a longer needle.
KPV: A three-amino-acid fragment of a larger hormone, studied for calming inflammation in the gut and skin. One of the peptides the FDA advisory panel reviewed in July 2026.
MOTS-c: A peptide encoded by mitochondrial rather than nuclear DNA, studied for how cells use energy and handle glucose. Early-stage science, mostly in animals.
PCAC Pharmacy Compounding Advisory Committee: The outside expert panel that advises the FDA on what compounding pharmacies should be allowed to use. It votes, but its votes are recommendations, not decisions.
peptide: A short chain of amino acids, which are the building blocks of protein. That is a chemistry definition, not a product category, which is why one word covers collagen powder, face serum, prescription drugs, and research vials.
reconstitute: Mixing a freeze-dried powder with sterile liquid to make it usable. Research peptides ship as powder because they keep far longer that way.
research-use-only: Sold as a laboratory material rather than as something to take. It is a legal category and a labeling requirement, not a quality grade.
Selank: A peptide from the same Russian research line as Semax, studied for anxiety. Human evidence outside Russia is thin.
Semax: A peptide developed in the Soviet Union and still prescribed in Russia, studied for attention, memory, and stroke recovery. Almost none of that research has been replicated elsewhere.
subcutaneous under the skin: Injected into the fat layer just under the skin rather than into a muscle or vein. Absorption is slower and steadier, and the needle is short.
TB-500: A synthetic fragment of thymosin beta-4, a protein involved in cell movement and repair. Studied mostly in animals for tissue healing.
titrate: Starting low and raising the dose in steps while watching how someone responds. Standard practice for anything with side effects that track dose.
TRT testosterone replacement therapy: Prescription testosterone for men whose own levels are low and who have symptoms. A medical treatment with real monitoring requirements, not a supplement.
WADA World Anti-Doping Agency: The body that sets the banned substance list for competitive sport. A compound being legal to buy says nothing about whether it will end a season.

Evidence & study design

How to read a claim. What kind of study it came from, and how much weight that kind of study carries.

CFU colony forming units: How live bacteria in a probiotic are counted. A higher count is not automatically better; the strain matters more than the number.
cohort study: Researchers follow a group over time and record what happens, without assigning anyone to anything. Good for spotting patterns, weak for proving cause.
contraindication: A reason someone specifically should not take something, such as a condition or another drug that makes it unsafe for them.
double-blind: Neither the participants nor the researchers know who got the real treatment until the study ends. It stops expectations on both sides from shaping the result.
efficacy: How well something works under study conditions, with selected participants and close supervision. Real-world results are usually smaller.
in vitro: In glass. An experiment in a dish or test tube rather than in a living body. What a compound does to cells in a dish often has little to do with what it does when swallowed.
in vivo: In a living body, whether animal or human, rather than in a dish.
IU international unit: A measure of biological activity rather than weight, used for vitamins A, D, and E. How many micrograms an IU equals is different for each one.
meta-analysis: A study that pools the results of many earlier studies to get one combined answer. Stronger than any single trial, and still limited by the quality of what went in.
NEJM New England Journal of Medicine: One of the most selective medical journals. Publication there is a signal about the size and rigour of a trial, not a guarantee the finding holds up.
placebo: An inactive stand-in given to the comparison group. People often improve on placebo, which is exactly why a treatment has to beat one rather than merely work.
preclinical: Research done in cells or animals, before any human testing. Promising preclinical results are the normal starting point, and most of them do not survive contact with human trials.
PREDIMED: A large Spanish trial that assigned thousands of people at cardiovascular risk to a Mediterranean diet or a low-fat diet. Much of the modern case for the Mediterranean pattern rests on it.
randomized: Assigned to a treatment group by chance rather than by choice. It is the single feature that separates a trial you can draw conclusions from and one you cannot.
RCT randomized controlled trial: A study where people are assigned by chance to the treatment or to a comparison group. Randomising is what lets you say the treatment caused the difference rather than the two groups being different to begin with.
RDA recommended dietary allowance: The daily amount of a nutrient judged enough for most healthy people. It is a floor for avoiding deficiency, not the dose used in supplement trials.
SELECT: The trial that tested semaglutide in people with obesity and heart disease but not diabetes, and found fewer cardiovascular events. It is why the drug is discussed as a heart drug at all.
systematic review: A structured search that gathers every study meeting set criteria, so the conclusion does not depend on which papers the author happened to like.

Food & nutrition

Fats, fibers, plant compounds, and the blood markers that food moves.

ALA: Usually alpha-linolenic acid, the plant omega-3 in flax, chia, and walnuts, which the body converts to EPA and DHA slowly and inefficiently. On a supplement label it can instead mean alpha-lipoic acid, an unrelated antioxidant.
anthocyanin: The polyphenol that makes berries, red cabbage, and purple sweet potato their colour. Studied mainly for blood vessel function and blood pressure.
beta-glucan: The specific soluble fiber in oats and barley responsible for their cholesterol-lowering effect. Around three grams a day is the amount used in the trials behind that claim.
carotenoid: The pigments behind orange, yellow, and deep green produce. Beta-carotene, lutein, and lycopene are the familiar ones, and fat in the meal helps you absorb them.
curcumin: The yellow compound in turmeric. Studied for inflammation and joint pain, and absorbed so poorly on its own that most trials pair it with black pepper or a special formulation.
DASH Dietary Approaches to Stop Hypertension: An eating pattern built in trials to lower blood pressure: heavy on vegetables, fruit, and low-fat dairy, light on sodium and red meat. One of the few diets with a trial behind its name.
DHA docosahexaenoic acid: The other long-chain omega-3 from seafood, and a structural part of the brain and retina. In a self-tanner, the same three letters mean dihydroxyacetone, an unrelated sugar that browns the skin.
dietary nitrate: A compound concentrated in beets and leafy greens that the body converts into nitric oxide, which relaxes blood vessels. The reason beetroot juice shows up in blood pressure and endurance research.
EPA eicosapentaenoic acid: One of the two long-chain omega-3 fats from seafood. It is the one most associated with calming inflammation and lowering triglycerides.
flavonoid: The largest group of polyphenols, found across nearly all plants. Anthocyanins and the catechins in tea are both flavonoids.
glycemic index: A ranking of how fast a food raises blood sugar compared with pure glucose. Useful as a rough guide, and it ignores portion size, which is what glycemic load adds.
glycemic load: The glycemic index adjusted for how much you actually eat. Watermelon scores high on index and low on load, because a serving holds little carbohydrate.
HbA1c glycated hemoglobin: A blood test showing your average blood sugar over roughly the past three months. One reading covers a season, which is why it is used to diagnose and track diabetes.
HDL high-density lipoprotein: The particle that carries cholesterol back to the liver for disposal. Higher levels track with lower heart risk, though raising it with drugs has not reliably helped.
homocysteine: An amino acid in the blood that rises when folate, B6, or B12 run low. Elevated levels track with cardiovascular and cognitive risk.
insoluble fiber: Fiber that does not dissolve. It adds bulk and keeps things moving, which is the part that matters for regularity.
insulin resistance: When cells stop responding well to insulin, so the body makes more of it to compensate. It usually precedes type 2 diabetes by years.
insulin sensitivity: How well your cells respond to insulin's signal to take up sugar from the blood. Better sensitivity means less insulin needed for the same job.
inulin: A prebiotic fiber in chicory root, onions, and garlic. Feeds gut bacteria well, and in larger amounts causes gas in people not used to it.
LDL low-density lipoprotein: The particle that carries cholesterol out to your tissues. More of it in the blood over years means more cholesterol deposited in artery walls, which is why it gets called the bad one.
lignan: A plant compound concentrated in flaxseed and sesame that gut bacteria convert into weak estrogen-like molecules. Studied for hormone-related outcomes.
methylfolate: The form of folate the body can use directly, without converting it first. Sold for people whose conversion is slow.
microbiome: The community of bacteria and other microbes living in your gut. It affects digestion, immune signaling, and mood, and diet shifts it within days.
MIND Mediterranean-DASH Intervention for Neurodegenerative Delay: A hybrid of the Mediterranean and DASH patterns weighted toward foods linked to slower cognitive decline, with berries and leafy greens singled out.
MTHFR: A gene coding for the enzyme that activates folate. Common variants slow that conversion down, which is the reason methylfolate supplements exist.
omega-3: A family of fats your body cannot make and has to get from food. The three that matter are EPA and DHA from seafood, and ALA from plants.
omega-6: Another family of essential fats, common in seed oils and nuts. Necessary in the diet; the argument is about proportion relative to omega-3, not about whether you need any.
phytosterol: A plant molecule shaped enough like cholesterol to compete with it for absorption in the gut. Two grams a day lowers LDL by roughly eight to ten percent.
polyphenol: A large family of plant compounds behind most of the colour and bitterness in produce, tea, coffee, olive oil, and cocoa. Much of the benefit of a plant-heavy diet is attributed to them.
postprandial: After a meal. A postprandial blood sugar spike is the rise in the couple of hours following eating.
prebiotic: Food for the bacteria already living in your gut, usually a particular fiber. Not the same as a probiotic, which is the bacteria themselves.
probiotic: Live bacteria taken in the hope they will do something useful in your gut. Effects are specific to the strain, so results with one say little about another.
resistant starch: Starch that escapes digestion in the small intestine and gets fermented by gut bacteria instead. Cooking and then cooling potatoes, rice, or pasta creates some.
satiety: The feeling of having eaten enough, and how long it lasts. Protein and fiber raise it most per calorie, which is what makes a meal hold you.
soluble fiber: Fiber that dissolves into a gel in water. It slows digestion, blunts blood sugar spikes, and binds cholesterol on its way out. Oats, beans, barley, and psyllium are the main sources.
sulforaphane: A compound formed when you chop or chew broccoli and other brassicas. It switches on the cell's own antioxidant defenses rather than acting as an antioxidant itself.
triglycerides: The main form fat takes in food and in your blood. High fasting levels usually track with excess refined carbohydrate, alcohol, or poor blood sugar control.

Body & physiology

What is happening underneath: nerves, hormones, cells, and the systems that run without being asked.

AMPK AMP-activated protein kinase: A sensor inside cells that notices when energy is running low and switches the cell from storing to burning. Exercise, fasting, and metformin all activate it.
antioxidant: A molecule that neutralises reactive compounds before they damage cells. Effective from food, and disappointing in most high-dose supplement trials.
ATP adenosine triphosphate: The molecule cells actually spend when they need energy. Everything you eat is ultimately converted into it.
autophagy: The cell's recycling process, breaking down damaged parts and reusing the material. Fasting and exercise increase it.
BDNF brain-derived neurotrophic factor: A protein that helps brain cells survive, connect, and adapt. Aerobic exercise raises it, which is part of why exercise shows up in cognitive research.
circadian rhythm: The roughly 24-hour internal clock setting sleep, hormones, temperature, and digestion. Morning light anchors it more strongly than anything else.
CNS central nervous system: The brain and spinal cord, as distinct from the nerves running out to the rest of the body.
cortisol: The main stress hormone. It should peak in the morning and fall through the day; the pattern being flat or reversed is what usually matters, not one number.
CYP3A4: A liver enzyme that breaks down a large share of all prescription drugs. Grapefruit and St John's wort interfere with it, which is why those interaction warnings exist.
diaphragmatic breathing: Breathing driven by the diaphragm, so the belly and lower ribs move rather than the chest and shoulders. It is the breath pattern nearly every calming practice is built on.
endothelium: The single layer of cells lining every blood vessel. It controls how vessels widen and narrow, and its decline is one of the earliest measurable steps toward heart disease.
GABA gamma-aminobutyric acid: The brain's main calming signal, the counterweight to its excitatory signals. Alcohol and sedatives work by amplifying it.
GI gastrointestinal: To do with the digestive tract, from mouth to colon. On a food label the same two letters usually mean glycemic index instead.
HPA axis hypothalamic-pituitary-adrenal axis: The chain from brain to adrenal gland that runs the stress response. Chronic stress changes how it responds, not just how much cortisol it makes.
HRV heart rate variability: The variation in time between heartbeats. More variation usually means a nervous system that is recovering well, which is why wearables track it.
IBS irritable bowel syndrome: Recurring abdominal pain with changes in bowel habit, where tests come back normal. Diagnosed by pattern, after ruling other things out.
INR international normalized ratio: A number describing how long blood takes to clot, tracked closely by anyone on warfarin. Vitamin K and several supplements move it.
MAOI monoamine oxidase inhibitor: An older class of antidepressant with serious food and drug interactions. Anything affecting serotonin needs checking against it.
mitochondria: The compartments inside cells that turn food and oxygen into usable energy. Muscle and brain cells are dense with them.
nitric oxide: A gas your blood vessel lining makes to tell vessels to relax and widen. More of it means easier blood flow and lower pressure.
NSDR non-sleep deep rest: A term for lying-down practices like yoga nidra that produce deep rest without sleep. Used for recovery when a nap is not possible.
oxidative stress: Damage that builds when reactive molecules made during normal metabolism outpace the body's ability to neutralise them. Implicated in aging and most chronic disease.
parasympathetic nervous system: The branch that slows you down and handles rest, digestion, and recovery. Slow exhales are the most direct way to switch it on.
PCOS polycystic ovary syndrome: A common hormonal condition involving irregular cycles, higher androgen levels, and often insulin resistance. A leading cause of difficulty conceiving.
PDE5 phosphodiesterase type 5: The enzyme that ends the nitric oxide signal telling blood vessels to relax. Sildenafil and tadalafil block it, so the signal lasts longer.
PMDD premenstrual dysphoric disorder: A severe form of premenstrual symptoms, heavy on mood, that disrupts daily life. A distinct diagnosis, treated differently from ordinary PMS.
PMS premenstrual syndrome: The mood and physical symptoms in the week or two before a period.
prostaglandin: A local signaling molecule that drives inflammation, pain, and the uterine contractions behind period cramps. Ibuprofen works by blocking their production.
senescence: When a cell stops dividing but refuses to die, and starts leaking inflammatory signals. Accumulating senescent cells is one of the recognised drivers of aging.
SSRI selective serotonin reuptake inhibitor: The most commonly prescribed class of antidepressant. Relevant here because several supplements interact with them.
sympathetic nervous system: The branch that speeds you up: heart rate, alertness, and the fight-or-flight response.
telomere: The protective cap on the end of a chromosome that shortens a little each time a cell divides. Used as one rough marker of cellular aging.
vagal tone: How strongly the vagus nerve is applying its brake to your heart rate. Higher tone tracks with better stress recovery and is trainable through slow breathing.
vasodilation: Blood vessels widening, which drops blood pressure and increases flow to the tissue downstream.

Movement & training

How muscles contract, how training loads work, and the anatomy named in the movement library.

concentric: The lifting half of a movement, where the muscle shortens. The push up out of a squat.
eccentric: The lowering half of a movement, where the muscle lengthens under load. It builds the most strength and causes the most soreness.
erector spinae: The columns of muscle running either side of the spine that hold you upright and extend your back.
fascia: The connective tissue wrapping every muscle and organ, in continuous sheets rather than separate pieces. Stiffness in one area can pull on another.
HIIT high-intensity interval training: Short hard efforts with recovery between them. Gets similar fitness gains to steady cardio in less time, at the cost of being harder.
hypertrophy: Muscle growing larger. Driven by hard sets taken near failure, enough protein, and enough recovery.
isometric: Holding a position under tension without moving, like a plank or a wall sit. Useful when a joint does not tolerate movement under load.
ligament: The tissue connecting bone to bone and limiting how far a joint travels. Poor blood supply is why ligament injuries heal slowly.
lumbar spine: The low back, the five vertebrae between ribs and pelvis. Built for stability, so it tends to complain when asked to do the mid-back's rotating.
posterior chain: The muscles down the back of your body: calves, hamstrings, glutes, and back. It drives most powerful movement and most desk-bound people underuse it.
progressive overload: Gradually asking more of a muscle over weeks, through more weight, more reps, or more control. Without it, training stops producing change.
proprioception: Your sense of where your body is without looking. It degrades with age and inactivity, and balance work rebuilds it.
range of motion: How far a joint can travel. Active range is what you can move through under your own control, which matters more than what someone can push you into.
sarcopenia: The age-related loss of muscle mass and strength. It starts in your thirties and accelerates later, and resistance training is the only thing shown to reverse it.
tendon: The tissue attaching muscle to bone. It adapts to training more slowly than muscle, which is why new lifters can outrun their own tendons.
thoracic spine: The mid-back, the twelve vertebrae your ribs attach to. It is built to rotate, and stiffness there usually shows up as shoulder or low back trouble.
VO2 max maximal oxygen uptake: The most oxygen your body can use during hard exercise. One of the strongest single predictors of how long you live, and it responds to training.

Skin & light

Ingredients, sun protection, skin structure, and the light-based devices sold for skin.

AHA alpha hydroxy acid: Water-soluble exfoliating acids like glycolic and lactic that loosen dead cells on the surface. Best for dryness, texture, and tone.
BHA beta hydroxy acid: Salicylic acid, which is oil-soluble and can work inside a pore rather than only on the surface. The reason it suits oily and congested skin.
broad-spectrum: A sunscreen that blocks UVA as well as UVB. Without it you are protected from burning but not from the aging and DNA damage UVA causes.
ceramide: A fat that makes up much of the skin's outer barrier, the mortar between cells. Dry and sensitive skin is usually short of it.
collagen: The main structural protein in skin, tendon, and bone. In skin it provides firmness, and production falls steadily from the mid-twenties.
comedogenic: Likely to block pores and cause blackheads or whiteheads. Ratings come from crude tests, so the label is a rough guide rather than a guarantee.
cytochrome c oxidase: An enzyme in the mitochondria that absorbs red and near-infrared light. It is the leading explanation for how red light therapy does anything at all.
elastin: The protein giving skin its snap back. Unlike collagen, the body barely replaces it after early adulthood, which is why sun damage to it is effectively permanent.
emollient: An ingredient that softens skin and smooths the gaps between surface cells. It is what makes a moisturiser feel nice rather than just work.
fibroblast: The skin cell that manufactures collagen and elastin. Nearly every anti-aging ingredient is ultimately trying to get these cells working again.
humectant: An ingredient that draws water into the skin. Glycerin and hyaluronic acid are the common ones.
hyaluronic acid: A humectant that holds many times its weight in water. It pulls moisture into the upper skin, and needs a moisturiser over it or it can pull the wrong way in dry air.
IPL intense pulsed light: A broad flash of light used for hair reduction and pigment. It works by being absorbed into dark pigment, so it works poorly on light hair and carries real risk on deeper skin tones.
irradiance: How much light power lands on a given area, written in milliwatts per square centimetre. It is what turns "hold it 6 inches away" into an actual dose.
keratinocyte: The main cell type of the outer skin layer. They are made at the bottom, travel up over weeks, and flake off the top.
LED light-emitting diode: The light source in at-home red light panels and masks. Unlike a laser, the light is not focused into a single beam, which is what makes it safe to use unsupervised.
nanometre nm: A billionth of a metre, the unit used to describe a light's colour. Red light devices are usually specified around 630 to 660 nm.
near-infrared: Light just past what the eye can see, roughly 800 to 900 nanometres. It penetrates deeper than red light, which is why devices aimed at joints and muscle use it.
niacinamide: A form of vitamin B3 applied to skin. Well tolerated, and studied for redness, oil, uneven tone, and barrier repair.
occlusive: An ingredient that forms a seal on the skin so water cannot escape. Petrolatum is the strongest and least glamorous example.
photoaging: Skin aging caused by sun rather than time: wrinkles, rough texture, and uneven pigment. It accounts for the large majority of visible facial aging.
photobiomodulation: The formal name for red light therapy: using red and near-infrared light at levels that change how cells behave without heating tissue.
retinoid: The family of vitamin A derivatives that speed up skin cell turnover and prompt new collagen. The best-evidenced anti-aging ingredient there is, and the one most likely to irritate at first.
retinol: The over-the-counter retinoid. Your skin converts it in two steps into the active form, so it works more gently and more slowly than prescription tretinoin.
sebum: The oil your skin makes. Necessary for the barrier, and the thing that makes skin look shiny when there is too much of it.
SPF sun protection factor: How much longer protected skin takes to burn from UVB compared with bare skin. It measures burning only, which is why "broad-spectrum" is the other half of the label.
transepidermal water loss: Water evaporating out through the skin. High loss means a leaky barrier, which is the measurable version of skin feeling tight and dry.
tretinoin: Prescription-strength retinoic acid, already in the form skin uses. Stronger and better studied than retinol, and more irritating.
UVA: The longer ultraviolet wavelengths. They penetrate deeper, drive most photoaging, pass through window glass, and do not cause an obvious burn.
UVB: The shorter ultraviolet wavelengths that cause sunburn and most skin cancers, and also make vitamin D in the skin.