Dictionary

Accelerated approval lets the FDA approve a promising drug for a serious disease faster, based on an early sign that it's likely to work, rather than waiting years for full proof. The tradeoff is that the drugmaker has to keep studying it afterward to confirm the drug actually delivers the expected benefit.

Think of actin as the scaffolding inside your cells — it gives them their shape and lets them move around. When you get injured, your body needs cells to travel to the damaged area to fix it. TB-500 helps kick this process into gear by boosting actin activity.

Activin A works alongside myostatin as another natural brake on muscle growth, and the same peptides that block myostatin often block this too.

Adipogenesis is just the process of your body making new fat cells. Drugs like semaglutide (Ozempic/Wegovy) help reduce this indirectly — when you eat less and your hormones are better regulated, your body doesn't need to create as many new fat cells.

An agonist is like a key that fits a lock and turns it. In your body, receptors are the locks and agonists are keys that open them and start a chain reaction. Semaglutide works by acting like a natural hormone your gut already makes, 'unlocking' the same effects.

Albumin is the most common protein floating in your blood — it acts like a delivery truck, carrying hormones and nutrients around your body. The DAC version of CJC-1295 is engineered to hitch a ride on albumin, which keeps it circulating in your body for days instead of just minutes.

Amino acids are the individual pieces that snap together to form peptides and proteins — like beads on a necklace. There are 20 of them, and the order they're strung together in determines what a peptide does in the body.

AMPK is like your body's 'low fuel' alarm. When your cells are running low on energy, AMPK kicks in and tells your body to burn fat, take in more sugar from the blood, and build more energy-producing machinery. MOTS-c can activate this same alarm — mimicking what happens when you exercise.

Angiogenesis is your body growing new blood vessels. This is a crucial part of healing — wounds and injured tissue need fresh blood supply to receive oxygen and nutrients. BPC-157 and TB-500 both help trigger this process, which is a big reason they're studied for recovery.

If an agonist is a key that opens a lock, an antagonist is a broken key — it fits in the lock but won't turn, and it also stops the real key from getting in. Antagonists are useful for blocking overactive biological signals, like turning down a system that's causing harm.

Your cells constantly produce waste products called free radicals, which can damage your DNA and speed up aging. Antioxidants neutralize these — think of them as a cleanup crew. GHK-Cu helps your body make more of its own antioxidant enzymes rather than just supplying them from the outside.

Apoptosis is your body's built-in self-destruct button for individual cells. When a cell is too damaged or no longer needed, it gets an orderly signal to shut down. This is normally healthy — but in conditions like heart disease, good cells can get this signal by mistake. SS-31 is studied for helping protect heart cells from dying prematurely.

The arcuate nucleus is a tiny area deep in your brain that acts as a hunger control center. It receives signals from your gut and hormones about whether you've eaten enough. Drugs like semaglutide work in part by sending 'full' signals to this area, reducing how hungry you feel.

ATP is basically the battery of your cells — it stores and delivers the energy they need to do everything from moving your muscles to thinking. Your body makes ATP inside tiny structures called mitochondria. SS-31 is being studied because it may help aging or damaged cells make ATP more efficiently again.

Autocrine signaling is when a cell talks to itself — it releases a chemical messenger that circles back and affects the same cell that released it. It's one of the ways cells regulate their own activity, almost like a built-in feedback loop.

This is the specific type of sterile water most often used to mix peptide powder into a liquid — the added preservative is what makes it safe to use from the same vial multiple times instead of needing a fresh one for every single dose.

The blood-brain barrier is a very tight security wall around your brain that stops most substances in your blood from entering brain tissue. Most drugs can't get through it. Selank and Semax are delivered through the nose specifically because the nasal passage has a direct route to the brain that skips this barrier.

BDNF is like fertilizer for your brain cells — it helps neurons grow, stay healthy, and form new connections. Low BDNF is linked to depression, cognitive decline, and poor memory. Selank and Semax are studied partly because they raise BDNF levels, which may explain improvements in focus and mood.

Bioavailability is how much of something you take actually makes it into your bloodstream and does something useful. Peptides swallowed as pills often get destroyed by stomach acid before they can be absorbed — that's why most research peptides are given by injection, which bypasses the digestive system entirely.

Bioregulatory peptides are tiny molecular messengers — often just 2 to 4 amino acids long — that can tell your genes to turn on or off. Despite being incredibly small, they can have surprisingly wide effects on how cells behave and age. Epithalon is the most studied example.

Before a compounding pharmacy can legally use an ingredient — including many research peptides — the FDA has to formally clear it for that purpose. Substances go through a multi-step review process, and where a peptide currently stands in that process (cleared, under review, or restricted) can change over time, which is why the compounding legality of peptides like BPC-157 has shifted repeatedly.

Cardiolipin is a special fat molecule found almost only inside the power-generating compartments of your cells. It's like the glue that holds the energy-producing machinery together. As we age, this glue degrades — and SS-31 is studied for its ability to stabilize it, potentially restoring cellular energy production.

Catabolism is the breakdown side of your metabolism — when your body tears down muscle or fat to use as fuel. It's the opposite of building. Intense exercise, illness, or stress push you into a catabolic state. Many peptides are studied for helping shift the body back toward building and repair.

Cell migration is exactly what it sounds like — cells moving from one place to another. When you injure yourself, repair cells need to travel to the damaged site. TB-500 helps activate the internal machinery that lets cells pick up and move, which is why it's studied for wound and tissue healing.

Senescent cells are sometimes called "zombie cells" — they're too damaged to keep working properly, but instead of dying off like they should, they stick around and release inflammatory signals that affect nearby healthy cells.

CMS is the government agency that runs Medicare and Medicaid and decides what those programs will pay for. It's a different agency from the FDA — the FDA decides whether a drug is safe and effective, while CMS decides whether, and how much, the government will help pay for it.

Chondrocytes are the workers that build and maintain your cartilage — the rubbery cushioning inside your joints. When joints wear down with age or injury, these cells need a boost. Pentosan polysulfate is studied for stimulating chondrocytes to produce more of the material that makes cartilage springy and durable.

A COA is basically a report card for a research compound. An independent lab tests the product and certifies what's in it, how pure it is, and whether it matches what the label says. Any reputable peptide vendor publishes these for every batch they sell — it's one of the most important things to look for when sourcing.

Collagen is the main structural protein holding your body together — it's in your skin, joints, tendons, and bones. Think of it as the body's scaffolding. Production naturally slows with age, leading to wrinkles and weaker joints. GHK-Cu is studied for its ability to stimulate the body to make more of it.

A compounding pharmacy is a specialty pharmacy that can custom-make a medication for a specific patient — including some peptides — rather than just dispensing pre-made, FDA-approved products off the shelf. Whether a compounding pharmacy can legally prepare a given peptide depends on which FDA list that peptide currently sits on.

Cortisol is your body's main stress hormone — it's released when you're under pressure and helps you respond to threats. In short bursts it's useful, but chronically high cortisol breaks down muscle, disrupts sleep, and suppresses the immune system. Ipamorelin is considered a cleaner option than some growth hormone boosters because it doesn't raise cortisol.

Cristae are the folds inside your mitochondria — the tiny power plants in your cells. More folds mean more surface area for energy production. As we age, these folds flatten out and energy production drops. SS-31 is studied for its ability to preserve these folds, which could restore cellular energy output.

Cyclical dosing means using something for a set period, then taking a break, then repeating. This is common with peptides because constantly stimulating the same receptor can make it less responsive over time — like how your body adapts to caffeine. Cycling prevents this tolerance from building up.

Cytokines are chemical messages that immune cells send to each other — they coordinate your body's response to infections, injuries, and stress. Too many pro-inflammatory cytokines causes chronic inflammation. Some peptides help 'turn down the volume' on the ones that drive excessive inflammation.

A Dalton is a tiny unit for measuring the weight of molecules — so small it's hard to visualize. Peptide weights are listed in Daltons to give you a sense of how big they are. Smaller peptides (a few hundred Daltons) can get into tissues more easily than larger ones (thousands of Daltons).

Desensitization is when your body gets used to a signal and starts ignoring it — like how you stop noticing a smell after being around it for a while. If you constantly stimulate a receptor with the same compound, it starts responding less. This is why peptide protocols often involve breaks.

Dopamine is the brain's 'feel good' and motivation chemical — it's released when you accomplish something, eat enjoyable food, or experience pleasure. It also controls movement. Low dopamine is linked to depression and lack of motivation. Several peptides interact with the dopamine system as part of how they work.

Elastin is the protein that makes your skin spring back after you pinch it, and keeps blood vessels flexible. Think of it as the rubber band of the body. Like collagen, elastin production slows with age, leading to sagging skin and stiffer arteries. GHK-Cu is studied for stimulating production of both.

Endogenous simply means 'made inside your body.' Many of the peptides in this database — like GHK-Cu and MOTS-c — actually exist naturally in your body. Scientists isolated them, figured out their structure, and then synthesized identical copies for research purposes.

Enkephalins are your body's natural painkillers and mood regulators — they're part of the same family as endorphins. Your body makes them naturally but they break down quickly. Selank works in part by blocking the enzymes that destroy enkephalins, letting them stay active longer and produce a calming effect.

eNOS is an enzyme inside your blood vessel walls that makes nitric oxide — a molecule that tells vessels to relax and widen, improving blood flow. BPC-157 activates eNOS, which is one reason it's linked to better circulation and faster healing in injured tissue that needs more blood supply.

EPO is best known for boosting red blood cells (which is why it's banned in sports), but part of the molecule also protects damaged tissue — some newer peptides try to get just that protective effect without the blood-doping part.

Exogenous is the opposite of endogenous — it means something that comes from outside the body. When you inject a research peptide, you're introducing an exogenous compound. Even if the peptide mimics something your body already makes, it's still considered exogenous because it was manufactured and administered externally.

FAERS is the FDA's giant database of reported side effects for approved drugs. After a medication has been on the market for years, researchers can comb through FAERS reports to spot rare or long-term safety issues that a shorter clinical trial might have missed.

The FAK-Paxillin pathway is a cellular communication chain that controls how cells attach to surfaces, multiply, and migrate. Think of it as an internal repair dispatch system. BPC-157 is thought to activate this system, which may explain its well-documented tissue repair effects in animal studies.

The FDA is the US government body that decides which drugs are safe and effective enough to be legally sold and prescribed. When a drug is 'FDA approved,' it means it went through years of clinical trials and the FDA reviewed the evidence and gave the green light. Most research peptides have not gone through this process.

Fibroblasts are the construction workers of your connective tissue — they produce collagen and the structural material that holds skin, tendons, and ligaments together. When you get a cut, fibroblasts rush in to rebuild. GHK-Cu is studied for activating more of these cells, speeding up the repair process.

FSH is a hormone released by the brain that plays a key role in reproduction — in women it triggers egg development, in men it supports sperm production. Kisspeptin-10 is studied for its ability to naturally stimulate FSH release, making it relevant for fertility treatments.

GABA is your brain's main 'calm down' chemical. It slows brain activity and reduces anxiety — it's what benzodiazepines (like Xanax) work on. Selank is studied because it appears to interact with the GABA system to produce calming effects, but without the sedation or addiction risk of prescription drugs.

Gastroprotective means 'protective of the gut.' BPC-157 was originally discovered in human stomach juice and has been studied extensively for its ability to heal stomach lining damage from ulcers, NSAIDs, and other irritants. It essentially helps protect and repair the digestive tract.

GHK is a naturally occurring mini-peptide — just three amino acids — found in your blood. On its own it does relatively little, but when it binds to a copper atom it becomes GHK-Cu, a potent compound that activates tissue repair, boosts collagen production, and influences gene activity. Think of the copper as turning on the switch.

GHS-R1a is the receptor in your brain that ghrelin — your hunger hormone — normally binds to. It also triggers growth hormone release. Ipamorelin is designed to fit this specific receptor like a key, stimulating growth hormone release without accidentally activating other receptors and causing unwanted side effects.

GIP is a hormone your gut releases when you eat, telling your pancreas to release insulin to manage blood sugar. Tirzepatide is special because it targets both this hormone's receptor AND the GLP-1 receptor simultaneously — a dual approach that's shown to produce greater weight loss than targeting just one pathway.

GLP-1 is a natural hormone your gut releases after eating — it tells your pancreas to release insulin, slows down digestion, and signals your brain that you're full. Drugs like Ozempic and Wegovy are engineered copies that last much longer in your body, amplifying all these effects for blood sugar control and weight loss.

This is a separate target from the GLP-1 receptor that some newer weight-loss compounds also activate — it's part of why those compounds are studied for boosting calorie burn, not just reducing appetite.

GnRH is the starting signal for the entire reproductive hormone chain — it's released in the brain and tells the pituitary gland to release the hormones that drive sex hormone production and fertility. Kisspeptin-10 sits one step above GnRH in this chain, acting as its master activator.

Growth hormone is made by the brain and drives muscle growth, fat burning, cell repair, and general vitality. It peaks during adolescence and declines steadily with age. CJC-1295 and Ipamorelin don't contain growth hormone — instead they signal your own pituitary gland to produce and release more of it naturally.

Half-life is how long it takes for your body to clear half of a substance from your system. A short half-life means it's gone quickly (Ipamorelin lasts about 2 hours); a long half-life means it stays active much longer (CJC-1295 DAC lasts about a week). This directly determines how often something needs to be dosed.

Hepatic simply means 'relating to the liver.' The liver is involved in many of the hormonal chain reactions that peptides trigger — for example, when growth hormone is released by the brain, it travels to the liver which then produces another hormone called IGF-1 that does the actual muscle-building work.

The HPG axis is the three-part hormonal communication chain that controls reproductive health — the brain sends a signal to the pituitary gland, which then sends signals to the testes or ovaries to produce sex hormones like testosterone and estrogen. Kisspeptin-10 essentially acts as the 'on switch' for this entire system.

HSDD is the medical name for ongoing, distressing low sexual desire. It's specifically the condition PT-141 is FDA-approved to treat — and currently the only officially approved use for that peptide.

The hypothalamus is a small but powerful region at the base of your brain that acts as the body's master control panel — it regulates hunger, thirst, body temperature, sleep, and hormone levels. Many peptides work by sending signals to the hypothalamus to change how your body behaves.

IGF-1 is the hormone that actually carries out most of growth hormone's muscle-building and tissue-repairing effects. Growth hormone is like the manager who gives the orders; IGF-1 is the worker who does the job. When CJC-1295 and Ipamorelin boost growth hormone, growth hormone then signals the liver to make more IGF-1, which drives the real results.

In vitro literally means 'in glass' — it refers to experiments done in a lab dish or test tube, not inside a living creature. When you see 'in vitro results,' it means the findings came from cells in a controlled lab setting. This is the earliest and most basic form of research, before animal or human testing.

In vivo means 'in the living' — research done inside a living animal or human, as opposed to in a test tube. Animal studies are in vivo, and human clinical trials are the most rigorous form. Most peptide research on this site is from in vivo animal studies, which is more meaningful than test-tube results but less definitive than human trials.

Incretins are hormones your gut releases when food arrives, alerting the pancreas to prepare insulin before blood sugar even spikes. Think of them as an early warning system. GLP-1 and GIP are the two main ones. Drugs like semaglutide work by mimicking incretins with a longer-lasting effect.

An IND is basically the FDA's permission slip for a drug to be tested on humans in clinical trials — even though it hasn't been fully approved yet. It means enough safety data exists to justify moving from animal studies to human testing. SS-31 has this status, meaning it's actively being tested in people.

Inflammation is your body's emergency response — redness, swelling, and pain that signal something is wrong and needs attention. Acute inflammation is necessary and helpful; chronic inflammation quietly damages tissues over time and is linked to most major diseases. Many peptides are studied specifically for their ability to calm chronic inflammation.

Interstitial cystitis is a long-term, painful bladder condition. It's the main FDA-approved use for pentosan polysulfate — the same compound now also being studied for joint and cartilage health.

An intramuscular injection goes directly into a muscle — like the thigh or shoulder — using a slightly longer needle. Because muscles have a rich blood supply, substances injected this way are absorbed into the bloodstream faster than if injected into the layer of fat under the skin.

Intranasal means delivered through the nose — like a nasal spray. For brain-targeting peptides like Selank and Semax, this is an effective route because the nasal lining is directly connected to the brain via the olfactory (smell) nerve pathway, allowing some compounds to reach brain tissue faster than via injection.

A kilodalton is 1,000 Daltons — a larger unit for measuring bigger molecules. When a peptide's weight is listed in kDa rather than Da, it just means the molecule is on the larger end. Larger molecules often have more complex effects but can be harder for the body to absorb or distribute.

KPV is a tiny three-amino-acid fragment of a larger hormone your body already makes. Despite its small size, it's a potent anti-inflammatory — it calms down an overactive immune signal called NF-κB. It's often paired with healing peptides like BPC-157 and TB-500 to help manage inflammation during recovery.

LH is the hormone that tells the testes to make testosterone in men, and triggers ovulation in women. It's released by the pituitary gland in the brain. Kisspeptin-10 essentially activates the upstream chain that causes LH to be released — making it a potential tool for supporting natural testosterone production and fertility.

Lipolysis is simply the process of your body breaking down stored fat and releasing it as fuel. Think of it as unlocking your fat stores for energy. When growth hormone is elevated — as it can be with growth hormone-stimulating peptides — lipolysis increases, which is why these compounds are associated with fat loss.

A loading phase is when you take higher doses at first to rapidly build up levels in your body, then drop to a lower maintenance dose to keep them there. It's like filling a tank before you start using it. TB-500 protocols often start with twice-weekly injections to 'load up,' then reduce to less frequent dosing.

MC3R and MC4R are two receptors in the brain involved in regulating appetite, energy, inflammation, and sexual arousal. PT-141 (Bremelanotide / Vyleesi) works by activating these receptors — this is why its effects on sexual desire are centrally driven through the brain, unlike Viagra which works on blood vessels.

Melanocortins are a family of hormones your body makes from a larger molecule. They act on melanocortin receptors in the brain and skin to control a surprising range of things: skin color, how much you eat, inflammation levels, and even sexual function. PT-141 mimics these signals to restore sexual desire.

Melatonin is the hormone your brain releases at night to signal it's time to sleep. It's made by the pineal gland and naturally declines with age, which is why sleep quality often worsens as we get older. Epithalon is studied for its ability to restore the pineal gland's normal melatonin output.

Mitochondria are the power plants of your cells — they take in nutrients and oxygen and convert them into the energy (ATP) your cells need to function. Every cell in your body has them, and their decline with age is increasingly linked to fatigue, disease, and aging itself. SS-31 and MOTS-c are two of the most exciting compounds being studied for restoring mitochondrial function.

Molecular weight is just how heavy a molecule is, measured in very small units called Daltons. It matters because smaller, lighter molecules tend to get into cells and tissues more easily. When you see 'MW' listed on a peptide profile, it gives you a sense of how the compound is likely to behave in the body.

Myostatin is a natural signal that keeps your muscles from growing indefinitely. Blocking it is like releasing a brake rather than pressing an accelerator.

NAD+ is a molecule every cell in your body needs to convert food into usable energy and repair damaged DNA. Levels drop as you age, which is part of why NAD+ supplementation has become popular in longevity circles — though dosing protocols vary widely and aren't yet standardized.

Neuroprotection means protecting your brain cells from damage or death. Neurons — the cells that make up your brain and nervous system — can be damaged by injury, toxins, stress, or aging. Several peptides are studied for their ability to shield neurons from this damage or help existing neurons survive longer.

NF-kB is like an inflammation volume knob inside your cells — when it's turned up too high for too long, it drives chronic inflammation throughout the body, which is linked to heart disease, autoimmune conditions, and accelerated aging. Several peptides work by turning this knob back down.

NGF is a protein that acts like a survival signal for nerve cells — it tells neurons to grow, maintain connections, and stay alive. Low NGF is associated with Alzheimer's disease and other neurodegenerative conditions. Selank raises NGF alongside BDNF, which together support brain health and cognitive function.

Nitric oxide is a tiny molecule your blood vessels produce to relax and widen — improving circulation. Think of it as a natural vasodilator. It's also involved in immune defense and nerve communication. BPC-157 is studied partly because it increases nitric oxide production, which may contribute to improved healing and circulation.

Off-label use is when a doctor prescribes an approved drug for a purpose it wasn't specifically approved for. It's legal and common — doctors use their clinical judgment. PT-141, for example, is FDA-approved for low sexual desire in women, but some clinicians prescribe it off-label for men with erectile dysfunction.

Orphan drug designation is a special FDA status meant to encourage companies to develop treatments for rare diseases, which might not otherwise be profitable enough to pursue. It gives the drugmaker benefits like tax credits and extra years of exclusive selling rights — but it's not the same thing as full drug approval.

Oxidative phosphorylation is the main way your mitochondria make ATP — the energy molecule your cells run on. Electrons pass through a chain of proteins inside the mitochondria, and the energy released powers ATP production. When this process becomes inefficient with age or disease, cells lose energy. SS-31 helps restore efficiency.

Oxidative stress happens when your body produces more harmful free radicals than it can neutralize. It's like rust forming on metal — it damages cells, DNA, and proteins over time. It's considered a major driver of aging and most chronic diseases. Multiple peptides on this site are studied for their ability to reduce it.

Paracrine signaling is when cells talk to their neighbors — one cell releases a chemical that affects the cells immediately around it. It's local communication rather than broadcasting a hormone throughout the whole bloodstream. This type of signaling is central to coordinated tissue repair, where groups of cells need to coordinate a healing response.

PEGylation is like wrapping a peptide in a protective layer so your body takes longer to break it down, meaning it stays active for longer and can be dosed less often.

Pentadecapeptide just means a peptide made of 15 amino acids. Despite being just 15 building blocks long, BPC-157 has a remarkably wide range of studied biological effects.

A peptide is a short chain of amino acids — the building blocks of all proteins. Think of it as a mini-protein. Your body uses peptides as messengers: they carry instructions between cells, act as hormones, regulate inflammation, trigger healing, and much more. The peptides studied on this site are either naturally occurring or engineered to mimic these natural messengers.

A peptide bond is the chemical 'snap' that connects two amino acids together — like a link in a chain. Every peptide is held together by a series of these bonds. They're strong but can be broken by enzymes in the body, which is part of why peptides taken orally often don't survive long enough to be absorbed.

Pharmacokinetics is the science of what your body does to a drug — how it absorbs it, moves it around, breaks it down, and eliminates it. When you see data about how long a peptide lasts or how it's best administered, that's pharmacokinetics. It's the 'body's handling' of a compound.

PCAC is a panel of outside experts the FDA consults before deciding whether compounding pharmacies can legally prepare certain substances, including peptides like BPC-157 and TB-500. Importantly, a PCAC vote is just a recommendation — the FDA still has to take its own formal action afterward, which can take many more months.

A Phase I trial is the very first time a drug is tested in humans — usually a small group of healthy volunteers. The main goal isn't to see if it works yet, it's to confirm it's safe and figure out the right dose. It's the first of three major stages a drug must pass before it can be approved.

Phase II trials are the second step in human clinical testing, now involving actual patients with the condition the drug targets. The goal is to see if the drug actually works and to continue monitoring side effects. A successful Phase II result means there's enough evidence to move to a large-scale final trial.

Phase III is the final major hurdle before a drug can be approved — large trials comparing the new drug against existing treatments or placebo across thousands of patients. This is where most drugs either prove themselves or fail. SS-31 is currently at this stage, making it one of the furthest along in clinical development among peptides on this site.

Phospholipids are fatty molecules that form the outer shell of every cell in your body — think of them as the bricks in the wall that surrounds each cell. Cardiolipin is a special phospholipid found only in the energy-producing compartments of cells. SS-31 targets it specifically to restore energy production in aging cells.

The pituitary gland is a pea-sized gland at the base of your brain that acts as the body's main hormone dispatcher. It releases growth hormone, controls the thyroid and adrenal glands, and regulates reproductive hormones. CJC-1295 and Ipamorelin work by signaling the pituitary to release more growth hormone.

Preclinical research means lab and animal studies that happen before any testing in humans. It's the research stage where scientists confirm a compound is interesting enough and safe enough to consider testing in people. Most peptides on this site have strong preclinical data — but that doesn't always predict how they'll behave in humans.

Prolactin is a hormone mainly known for its role in milk production, but it also affects immune function, mood, and sexual function in both men and women. Elevated prolactin in men is associated with low testosterone and reduced libido. Ipamorelin is popular among growth hormone-stimulating peptides partly because it doesn't raise prolactin.

Proteoglycans are large shock-absorbing molecules that make up a big part of cartilage and other connective tissue. They act like sponges, holding water and giving cartilage its ability to compress and spring back. When cartilage wears down, proteoglycan loss is a major factor. Pentosan polysulfate helps stimulate more of these to be produced.

Some hormones work best in short bursts rather than a constant drip — growth hormone and the hormones involved in fertility are good examples. That's part of why timing and dosing pattern matter for peptides that trigger these systems.

Reactive oxygen species — also known as free radicals — are unstable molecules your cells produce as byproducts of energy production. In small amounts they're useful; in excess they damage DNA, proteins, and fats throughout the body. This is oxidative stress, and it accelerates aging. SS-31 is studied partly for dramatically reducing ROS production in mitochondria.

A receptor is a protein on the surface (or inside) of a cell that acts like a docking port for specific molecules. When the right molecule lands on the right receptor, it triggers a chain of events inside the cell. Peptide drugs work by fitting into specific receptors to either activate them (agonists) or block them (antagonists).

Reconstitution just means adding liquid to a peptide that comes as a dry powder, so it can actually be injected. Almost every peptide ships as a freeze-dried powder in a small vial because that form stays stable for a long time — once you add the liquid (usually a special sterile water called bacteriostatic water), the clock starts ticking, and the mixed solution typically needs to be refrigerated and used up within a matter of weeks.

A research compound is a substance that's been synthesized for scientific study and has not gone through the FDA approval process for human use. Many peptides on this site fall into this category — they show promise in lab and animal research, but haven't yet been evaluated in the clinical trials required for human approval. This is a critical legal and safety distinction.

Satellite cells are like a reserve crew of muscle-building cells that mostly sit inactive until your muscles are damaged (like after a hard workout) — then they wake up and help rebuild.

A secretagogue doesn't add a hormone to your body directly — it tells a gland to release more of a hormone it already makes. Most of the growth-hormone-related peptides on this site work this way.

A senolytic is designed to clean out the "zombie cells" described under Cellular Senescence, without hurting the healthy cells around them.

Serotonin is often called the 'feel good' neurotransmitter — it plays a major role in mood, emotional stability, appetite, and sleep. Low serotonin is linked to depression and anxiety. Several peptides interact with the serotonin system as part of their mechanism, which may explain some of their mood-related effects.

Somatotrophs are the specific cells in your pituitary gland that make and release growth hormone. They have receptors on their surface that respond to growth hormone-releasing hormone (GHRH). CJC-1295 is designed to bind these receptors and tell somatotrophs to produce and release more growth hormone.

A subcutaneous injection goes into the layer of fat just below the skin — typically in the stomach, thigh, or upper arm — using a short, thin needle. It's the most common way research peptides are administered. Absorption is slower than a muscle injection but more gradual and steady, which is often preferred.

Synovial fluid is the slippery liquid inside your joints — it acts as both a lubricant and a nutrient supply for the cartilage, which has no blood vessels of its own. When synovial fluid quality degrades (as it can with arthritis), joints become stiff and painful. Pentosan polysulfate is studied for restoring synovial fluid quality.

T-cells are one of your immune system's main fighters — they identify and destroy cells infected by viruses or that have turned cancerous. They mature in the thymus gland. Thymosin Alpha-1 is studied for stimulating T-cell development and activity, which is why it's used in many countries as an immune-boosting therapy for hepatitis and cancer.

Telomerase is an enzyme that rebuilds the protective caps on your chromosomes (telomeres) after they shorten. Most adult cells have very little telomerase activity — once those caps wear down, cells stop dividing. Epithalon is studied because it may activate telomerase, potentially allowing cells to replicate longer and age more slowly.

Telomeres are like the plastic tips on shoelaces — they cap the ends of your chromosomes and protect the DNA inside. Every time a cell divides, these caps get a little shorter. When they run out, the cell can no longer divide and either stops working or dies. This is considered one of the core mechanisms of aging, and Epithalon is the most studied peptide targeting it.

Tesamorelin is a growth-hormone-boosting peptide that's actually approved by the FDA — but only for one specific use: reducing excess belly fat in HIV patients with a fat-redistribution condition called lipodystrophy. Any other use is considered off-label.

A tetrapeptide is a peptide made of exactly four amino acids. Despite being incredibly tiny, tetrapeptides like Epithalon and SS-31 can have powerful effects in the body. This shows that you don't need a large, complex molecule to produce a significant biological response — sometimes four building blocks is enough.

Thymosin is a family name for a group of peptides originally discovered in the thymus gland — the immune system's training center. Different thymosins do different things: Thymosin Alpha-1 boosts immune defenses, while Thymosin Beta-4 (which TB-500 is derived from) promotes tissue repair and healing. They share a family name but have very different roles.

The thymus is a small gland behind your sternum where immune T-cells are trained and matured before being deployed to fight infection. It's most active in childhood and gradually shrinks with age — which is part of why immune function declines as we get older. Thymosin Alpha-1 mimics some of the immune-training signals the thymus naturally produces.

A transcription factor is a protein that acts like an on/off switch for genes. It binds to a specific section of DNA and either turns a gene on (allowing it to be read and produce a protein) or turns it off. NF-kB, for example, turns on inflammation genes; when peptides suppress it, those inflammation genes get switched off.

Tuftsin is a tiny natural peptide your body makes from antibodies. It helps regulate immune function and has some brain-affecting properties. Selank was created as an improved version of tuftsin — engineered to be more stable in the body, longer-lasting, and able to cross into the brain more effectively.

Twincretin is a nickname for tirzepatide (Mounjaro/Zepbound) because it targets two gut hormones at once — GIP and GLP-1 — instead of just one. This dual approach appears to produce greater appetite suppression and weight loss than drugs targeting only GLP-1, which is why tirzepatide has shown the largest weight loss numbers of any approved drug to date.

Vasodilation is when your blood vessels widen and relax, allowing more blood to flow through. This lowers blood pressure and improves circulation to muscles, organs, and healing tissue. Your body's main tool for this is nitric oxide. BPC-157 is studied for promoting vasodilation by boosting nitric oxide production.

VEGF is your body's main signal for growing new blood vessels. When tissue is injured, VEGF is released to attract blood vessel growth into the area, bringing oxygen and nutrients needed for repair. BPC-157 is studied partly because it turns up VEGF production, which may explain its strong healing effects in animal studies.