Peptide Glossary

Sterile water with a tiny amount of preservative, used to mix powdered peptides.

One vial holding more than one compound, mixed together by the seller. Working out a dose means working out each ingredient separately, because they are rarely present in equal amounts.

How strong the mixed peptide is, in milligrams per milliliter (mg/mL). More water makes it weaker; less water makes it stronger.

A stretch of time using a compound followed by a break. Most cycling patterns come from community practice. Very few have been tested.

Adding more liquid to make a mix weaker. The amount of peptide in the vial does not change. It is just spread through more water, so each draw is bigger.

Freeze-dried into a powder so it keeps longer. That is the white cake or dust in the bottom of an unmixed vial.

Units of dose. 1 milligram (mg) equals 1,000 micrograms (mcg).

Mixing a powdered peptide with liquid (bacteriostatic water) so it can be drawn into a syringe.

Using more than one compound at the same time. Almost no combinations have been tested together in people, so a stack is usually built on guesswork.

Water with nothing added to stop bacteria growing. It works for a single dose, but a vial mixed with it should not be kept and used again.

Starting at a low dose and increasing it slowly over time so your body adjusts and side effects stay mild.

The small amount of liquid left sitting inside the needle and hub after you inject. On very small doses it can be a real share of what you meant to take.

The spot on the body where you inject. Moving it around gives the skin and fat underneath time to recover between doses.

An injection into a muscle, using a longer needle.

An injection into a vein. It needs training and equipment and is not something to do at home.

An injection just under the skin, into the fat layer, usually with a short, thin insulin needle.

The marks on an insulin syringe. 100 units equals 1 mL. They measure how much liquid you draw, not the dose in milligrams.

Something that switches a receptor on. The opposite is an antagonist. It blocks the receptor instead.

Pain from something that should not hurt at all: a bedsheet, a light breeze, the weight of a sleeve. It is a specific neurological term and a stronger claim than most people mean when they use it.It appears among the preferred terms grouped under dysesthesia on the Wegovy label, and in case reports for tirzepatide.

The building blocks that link together in a chain to make a peptide or a protein. The order they sit in is what makes one peptide different from another.

A hormone released alongside insulin that acts on fullness through different brain circuits from the incretins. Cagrilintide and eloralintide are amylin receptor agonists.It matters because the next generation of weight-loss drugs pairs an amylin drug with an incretin rather than stacking two incretins. CagriSema is cagrilintide with semaglutide; EloraTZP is eloralintide with tirzepatide. Both approved GLP-1 labels advise against combining their drug with another GLP-1 agonist, while manufacturers develop amylin pairings deliberately.

A compound built to copy a natural one with small deliberate changes, usually so it lasts longer or holds onto its target more tightly.

A large immune protein, far bigger than a peptide, engineered to lock onto one specific target. These are made by drug companies and are not sold as research powders.

GHK without copper, the copper-free form of the peptide. The literature treats it as a separate substance from GHK-Cu rather than a variant, because the copper is central to most of what GHK-Cu is claimed to do. It appears in this market both as a product in its own right and as an ingredient in the folk practice of adding copper-free peptide to a GHK-Cu vial to reduce stinging.

How much of a dose actually reaches your bloodstream. Most peptides survive stomach acid badly, so most of them are injected instead of swallowed.

Very short peptides from a Russian research tradition, usually two to four amino acids long, sold for supporting a specific organ. Human evidence is thin and most of it is published in Russian.

A side effect that comes from the whole family of drugs rather than one member of it. If a symptom appears across semaglutide, tirzepatide and retatrutide at different rates, it is a property of how these drugs work, not of any one of them.Useful in two directions. It tells you a symptom is probably not a bad vial or a bad batch. And it tells you switching to another drug in the same class may not fix it, which is the mistake people make most often.Abnormal skin sensation is a class effect across the incretin drugs: 0.4% on tirzepatide at its top dose, 4.9% on semaglutide tablets, and 12.5% to 20.9% on retatrutide.

Short for Drug Affinity Complex. An attachment added to a peptide so it grabs onto a blood protein and stays in the body for days instead of minutes.

An unpleasant or wrong sensation in the skin: burning, tingling, crawling, or the feeling people describe as sandpaper. It is the term the phase 3 retatrutide trials use, and it appears on both the Wegovy and Zepbound labels.Distinct from hyperesthesia, which is ordinary sensation turned up too high, and from allodynia, which is pain from something that should not hurt at all. Most people describing skin sensitivity on these drugs are describing dysesthesia or hyperesthesia rather than true allodynia.The useful thing to say to a clinician is "abnormal skin sensation" plus a description of what it feels like, rather than a label they may disagree with.

Burping. It is the word on the label, which is why you will find it in an adverse reactions table and nowhere in ordinary speech. It appears in the tirzepatide label at 4 to 5% by dose against 1% on placebo.What people call sulfur burps is eructation with a taste, generally attributed to food sitting longer in the stomach.

A short piece cut out of a larger natural protein. A fragment can behave very differently from the whole protein it came from, so evidence about one does not transfer to the other.

The hunger hormone. Some growth hormone compounds work by copying it, so they can make you noticeably hungrier.

A natural signal telling the pituitary gland to release growth hormone. Several compounds copy it.

A second, separate signal that also triggers growth hormone release, through a different door than GHRH. This is why the two types are often used together.

A natural gut hormone that lowers appetite and blood sugar. Drugs that copy it, like semaglutide, are used for weight loss.

A compound that nudges your body to release more of its own growth hormone, rather than injecting the hormone itself.

How long a compound stays active in your body. A longer half-life means you inject less often. See the half-life chart for every compound.

Ordinary sensation turned up too high. Touch registers as more intense than it should, so a shirt seam or a shower at a normal temperature becomes uncomfortable. The phase 2 retatrutide trial used this term; the phase 3 trials use dysesthesia.

A hormone released by the gut after eating that signals the pancreas and the brain. GLP-1 and GIP are incretins, and the drugs in this class are built to mimic them.The word is how you tell these drugs apart. Semaglutide acts on the GLP-1 receptor. Tirzepatide acts on GLP-1 and GIP. Retatrutide adds glucagon, which is a third pathway. More receptors has so far meant more weight loss and more side effects.Amylin is not an incretin, which is why combining an amylin drug with an incretin is a different proposition from combining two incretins.

A natural brake on muscle growth. Several compounds are built to block it, though human results have been far smaller than the animal work suggested.

A peptide is a short chain of amino acids. A few items here (like MK-677 or methylene blue) are small molecules, not true peptides, but people use them the same way.

A docking point on a cell that a compound attaches to. If a cell has no matching receptor, the compound does nothing to it.

An older class of diabetes tablet that makes the pancreas release insulin. Gliclazide and glipizide are examples.It appears on this site for one reason. Both the Wegovy and Zepbound labels scope their hypoglycaemia warning to people also taking insulin or a sulfonylurea. For someone on a GLP-1 alone without diabetes medication, low blood sugar is not the expected explanation for feeling shaky or tired, and it is the explanation forum replies reach for first.

The time after a dose at which the drug reaches its highest concentration in the blood. It is in section 12.3 of a label, under pharmacokinetics.It explains patterns people notice and cannot account for. Semaglutide reaches maximum concentration 1 to 3 days after the injection and tirzepatide 8 to 72 hours after, which is why the day after a shot comes up so often in accounts of fatigue.Not the same as half-life, which describes how long the drug takes to clear rather than how long it takes to peak.

Having too little fluid in the body, which is what the labels say rather than dehydration. It appears in the GLP-1 labels alongside warnings about kidney injury, because losing fluid through vomiting or diarrhea, or simply drinking much less, can reduce blood flow to the kidneys.Worth knowing because the label language does not sound like the everyday problem it describes. Eating much less means drinking much less, since food carries a substantial share of daily water.

Research done in rats, mice or other animals. Most findings do not repeat in people, so an animal result is a reason to keep looking. It is not a reason to act.

A study that gives a treatment to people under a written plan and measures what happens. It is the only kind of evidence that can show something works in humans.

One of two ways a trial can report its result. The efficacy estimand estimates what would have happened if everyone had stayed on the drug as directed. The treatment-regimen estimand reports what happened to everyone who was randomized, including those who stopped or switched.The gap between them can be large. In TRIUMPH-1, retatrutide's weight loss at 12 mg was 28.3% on the efficacy estimand and 25.0% on the treatment-regimen estimand. Neither figure is wrong. They answer different questions: the first is closer to "what if I take it properly", the second to "what happened to a group of real people".Which figure a company quotes in a press release is usually the higher one. Compound pages on this site show both where both are reported.

The result a trial said in advance that it would measure. A study can be reported as positive and still have missed the endpoint it set out to hit.

Done in a dish or a test tube, on cells outside a living body. It is the earliest kind of evidence there is.

Other scientists checking a paper before a journal publishes it. It filters out some bad work. It does not make a finding true.

A dummy treatment given for comparison. Without one it is very hard to tell a real effect apart from expectation and time passing.

A paper posted publicly before peer review. It has been written by researchers and made available, and it has not yet been checked by other researchers in the field or accepted by a journal.Preprints are not worthless and they are not finished. Findings can change between a preprint and publication, and some are never published at all. Where we cite one, we say so and we say what it does and does not establish.Two examples on this site: the finding that the GLP-1 receptor appears in human endometrium, and the study of self-reported retatrutide side effects on Reddit. Both are useful and neither is settled.

The one result a trial was designed to measure, chosen before it started. Everything else is a secondary endpoint, and the distinction decides how much weight a finding carries.A trial that hits its primary endpoint has shown what it set out to show. A finding from a secondary endpoint is weaker, because the trial was not built to test it and because testing many things raises the chance of one looking good by accident.This catches people out in comparisons. In Lilly's EloraTZP trial, the primary endpoint was the combination against placebo. The comparisons against tirzepatide, which are the numbers everyone quoted, were secondary.

Deciding by chance who gets which treatment, so the two groups are comparable. Studies that skip this are much easier to read the wrong way.

A company's summary of a trial's main findings, released before the full paper. Topline results are a press release, not peer-reviewed data. They give the headline numbers the company chose to report and usually omit the detail: the full adverse event table, the subgroup results, the things that did not work.The distinction matters on this site because trials in the same program are often at different stages. TRIUMPH-1 and TRIUMPH-2 are published papers. TRIUMPH-3 and TRIUMPH-4 are company announcements. We label which is which every time, because a figure from one is not the same grade of evidence as a figure from the other.Topline results are not unreliable. They are incomplete, and the parts omitted are chosen by the company.

The trial result that counts everyone who was randomized, including people who stopped the drug, switched to something else, or had rescue treatment. It is the more conservative of the two estimands and the one closer to what a population actually experiences.For retatrutide at 12 mg in TRIUMPH-1 it was 25.0%, against 28.3% on the efficacy estimand.Worth knowing when a trial had a high dropout rate, because that is where the two figures separate most.

The stages of human testing. Phase 1 checks safety in a small group, phase 2 looks for an effect, and phase 3 tests it against a comparison in a large group.

The two kinds of compounding pharmacy in US law. A 503A pharmacy prepares medicine for one named patient. A 503B outsourcing facility makes larger batches under stricter manufacturing rules.

Prohibited by the World Anti-Doping Agency (WADA); using it can disqualify a competing athlete.

The most serious warning the FDA puts on a drug label, printed inside a black border. It flags a risk considered severe enough to sit above everything else on the label.

The FDA's list of ingredients that compounding pharmacies are allowed to use. A substance can sit under review on it for years without anything being decided either way.

A licensed pharmacy preparing a medicine to order. Being allowed to compound something is not the same as the FDA approving it, and the two get mixed up constantly.

Reviewed by the FDA and cleared for a specific use, in a specific form, at a specific dose. Approval for one use is not approval for another, and approval in another country is not approval here.

Still being tested in clinical trials and not yet approved or legally sold for general use.

A doctor prescribing an approved drug for something other than its approved use. This is legal and common, and it is different from a compound having no approval at all.

A status given to treatments for rare conditions to make them worth developing. It is an incentive, not an approval, and a compound can hold it while being approved for nothing.

The FDA advisory committee that reviews compounding ingredients. It recommends. It does not approve, and the FDA does not have to follow what it says.

No approved dose or use in people. Sold for research and not reviewed by the FDA for safety or quality.

A lab report on a batch of product. It only means something if it names the batch you actually received, comes from an independent lab, and can be checked with that lab.

A lab method that separates out everything in a sample so the amounts can be measured. It shows how much of the main ingredient is there. It does not confirm that the main ingredient is the right molecule.

The loosely held copper in a copper peptide solution, as distinct from copper properly bound to the peptide. It matters because bound copper is the intended active and loose copper is the part that can irritate tissue and drive oxidation. A 2026 review in *Pharmaceutics* proposes it be measured and specified by route, with a ceiling of 1 mol% of total copper for injectable products and 5 mol% for topical, and reports that published delivery studies usually do not measure it at all. No seller's certificate of analysis reports it.

A lab method that weighs molecules to confirm what they are. HPLC answers how much is in the sample. This answers what it is.

How much of the copper in a copper peptide product is actually held by peptide, rather than loose. A product can show the correct total copper and still have poor occupancy. The same 2026 review proposes a target of 0.95 to 1.05 copper per peptide at lot release. It is the measurement that would distinguish a well-made copper peptide from a badly made one, and nothing in the research-peptide market reports it.

The share of a sample that is the intended compound, usually given as a percentage. A high purity number on the wrong molecule is still the wrong molecule.