Peptide glossary

The 40 terms the peptide atlas and the guides lean on, each defined so it stands on its own. Definitions describe; none of them is a dose recommendation.

Amylin analog: An amylin analog is a drug that mimics amylin, a hormone the pancreas releases alongside insulin that promotes fullness and slows stomach emptying. Cagrilintide is studied mainly with semaglutide as CagriSema; petrelintide and eloralintide are being tested on their own for weight loss; amycretin combines amylin and GLP-1 activity in one molecule. Every amylin analog in the atlas is investigational.; In the atlas: Cagrilintide, Petrelintide, Eloralintide; Read: CagriSema: A Tracking Guide for a Cagrilintide and Semaglutide Combination; See also: GLP-1 receptor agonist
Aromatase inhibitor (AI): An aromatase inhibitor (AI) is a drug that blocks aromatase, the enzyme that converts testosterone and other androgens into estrogen. Anastrozole, letrozole and exemestane are prescription breast-cancer medicines in this class. In androgen protocols they are used to control estrogen, which is why the atlas pairs them with estradiol bloodwork: driving estrogen too low harms joints, libido, mood, lipids and bone density.; In the atlas: Anastrozole, Letrozole, Exemestane; Read: Anastrozole: A Tracking Guide for the Aromatase Inhibitor; See also: SERM, Titration
Bacteriostatic water also BAC water: Bacteriostatic water is sterile water for injection containing 0.9% benzyl alcohol, a preservative that inhibits bacterial growth after the vial stopper has been punctured. It is the standard liquid for reconstituting multi-dose peptide vials. Plain sterile water and saline contain no preservative, so they suit a single immediate preparation, not a vial drawn from over weeks. An opened vial is commonly kept for about 28 days.; Read: Bacteriostatic Water: Why It Matters and How to Use It · How to Calculate Peptide Reconstitution: The Simple Math · Reconstitution calculator; See also: Reconstitution, Peptide stability
Baseline: A baseline is a set of measurements taken before a protocol starts, used as the reference point for judging whether anything changed. It usually means daily scores logged for at least a week before the first dose, plus a blood panel drawn one to two weeks before it. Without one, the first week on a compound becomes the comparison by accident, which makes later weeks look more dramatic than they are.; Read: Build Your First Peptide Protocol: A 5-Step Framework · Bloodwork During a Peptide Cycle: What to Watch; See also: Cycle, Washout
Bioavailability: Bioavailability is the fraction of an administered dose that reaches the bloodstream unchanged. An intravenous dose is 100% bioavailable by definition; every other route delivers less. Most peptides have very low oral bioavailability because digestive enzymes break them down, which is why they are injected. Oral exceptions are engineered: oral semaglutide is formulated with an absorption enhancer, and orforglipron is a small molecule rather than a peptide.; In the atlas: Oral Semaglutide, Orforglipron; Read: Oral Semaglutide 25 mg: A Tracking Guide for the Wegovy Pill; See also: Subcutaneous (SC), Intranasal
Blend: A blend is a single vial containing two or more peptides premixed at a fixed ratio, such as BPC-157 with TB-500. It saves injections but locks the ratio: neither compound can be adjusted on its own, and an effect or side effect cannot be pinned to one ingredient. Ratios vary by vendor, and a "proprietary blend" with no per-peptide amounts cannot be dosed or logged accurately.; In the atlas: BPC-157 / TB-500 blend, Wolverine blend; Read: KLOW and Other Multi-Peptide Blends: The Attribution Problem; See also: Stack, Certificate of analysis (COA)
Certificate of analysis (COA): A certificate of analysis (COA) is a document reporting laboratory test results for one specific manufacturing batch of a compound. For peptides it usually states identity, often confirmed by mass spectrometry, and purity, commonly measured by high-performance liquid chromatography (HPLC). A COA covers only the batch number printed on it and is only as trustworthy as the laboratory that issued it; independent third-party testing carries more weight than a seller's own paperwork.; In the atlas: AOD-9604, Wolverine blend; Read: KLOW and Other Multi-Peptide Blends: The Attribution Problem; See also: Research chemical
Clinical trial phases also Preclinical, Phase 1, Phase 2, Phase 3: Clinical trial phases are the stages a drug passes through in human testing before it can be approved. Preclinical work comes first, in cells and animals. Phase 1 tests safety and dosing in a small group, Phase 2 looks for efficacy and the right dose, and Phase 3 confirms benefit and safety in large populations to support a regulatory filing. Many atlas entries rest mainly on preclinical or early-phase evidence.; In the atlas: Retatrutide, Petrelintide; Read: Retatrutide: Tracking a Triple-Agonist Weight-Loss Compound; See also: Off-label use, Research chemical
Cycle: A cycle is a defined block of time during which a compound is taken, followed by a planned stop. Its length, dose frequency and dose range are fixed before the first dose and not changed midway, so the result can be judged cleanly. A cycle is usually followed by a washout of equal or longer length. Cycle lengths in the atlas and guides describe what is reported, not what to do.; Read: Build Your First Peptide Protocol: A 5-Step Framework · BPC-157: A Beginner's Guide to Dosing and Tracking; See also: Protocol, Washout, Baseline
Desensitization: Desensitization is the fading response that develops when a receptor is stimulated too often or too strongly, so the same dose produces a smaller effect over time. It is well documented for the growth-hormone-releasing peptides, fastest with hexarelin, and for sustained high doses of HCG or gonadorelin on the reproductive axis. It is the usual reason those compounds are run in short cycles rather than continuously.; In the atlas: Hexarelin, Ipamorelin; Read: Hexarelin: A Tracking Guide With a Desensitization Warning; See also: Ghrelin mimetic, Cycle
Ester: An ester is a chemical group attached to a steroid hormone such as testosterone that controls how quickly the hormone is released from an oil injection into the blood. Enzymes cleave the ester off to free the active hormone. Short esters such as propionate and acetate release quickly and are injected often; long esters such as enanthate, cypionate and decanoate release slowly, so injections are spaced further apart.; In the atlas: Testosterone Propionate, Testosterone Enanthate, Testosterone Cypionate; Read: Testosterone Propionate: A Tracking Guide for the Short Ester; See also: Half-life, Intramuscular (IM)
GH secretagogue also Growth hormone secretagogue, GHS: A growth hormone secretagogue (GHS) is a compound that makes the pituitary gland release more of the body's own growth hormone, instead of supplying growth hormone directly. Used broadly, as on this site, it covers GHRH analogs such as sermorelin and CJC-1295 and ghrelin mimetics such as ipamorelin and MK-677; narrower usage means ghrelin-receptor agonists only. Raising growth hormone raises IGF-1, the marker bloodwork follows.; In the atlas: Ipamorelin, MK-677, Sermorelin; Read: Ipamorelin and CJC-1295: A Practical Tracking Guide; See also: GHRH analog, Ghrelin mimetic, IGF-1
Ghrelin mimetic also GHRP, Growth-hormone-releasing peptide: A ghrelin mimetic is a compound that activates the ghrelin receptor (GHS-R1a) on the pituitary to trigger a pulse of growth hormone. The injectable peptides in this group are called growth-hormone-releasing peptides (GHRPs): GHRP-2, GHRP-6, hexarelin and ipamorelin. MK-677 is an oral, non-peptide member. The older GHRPs also raise appetite, cortisol and prolactin; ipamorelin is valued for being more selective.; In the atlas: GHRP-2, GHRP-6, Ipamorelin, MK-677; Read: GHRP-6: Tracking the Appetite-Forward GH Secretagogue; See also: GH secretagogue, GHRH analog, Desensitization
GHRH analog: A GHRH analog is a synthetic version of growth-hormone-releasing hormone, the signal from the hypothalamus that tells the pituitary to release growth hormone. Sermorelin, tesamorelin and both forms of CJC-1295 belong to this class. CJC-1295 No-DAC (Mod GRF 1-29) acts for about half an hour, while CJC-1295 with DAC binds to albumin in the blood and lasts about a week. They are often paired with a ghrelin mimetic.; In the atlas: Sermorelin, Tesamorelin, CJC-1295 No-DAC (Mod GRF 1-29), CJC-1295 with DAC; Read: CJC-1295 with DAC: Tracking the Long-Acting GHRH Analog; See also: GH secretagogue, Ghrelin mimetic, Half-life
GLP-1 receptor agonist also GLP-1 agonist, GLP-1RA: A GLP-1 receptor agonist is a drug that mimics glucagon-like peptide-1, a gut hormone released after eating, to slow stomach emptying, reduce appetite and improve blood-sugar control. Semaglutide, liraglutide and dulaglutide are approved examples. Newer agents add targets: tirzepatide is a dual GLP-1/GIP agonist, and the investigational retatrutide a GLP-1/GIP/glucagon triple agonist. Doses are raised in steps to keep stomach side effects tolerable.; In the atlas: Semaglutide, Tirzepatide, Retatrutide; Read: Tracking Semaglutide: Dose Titration and Side Effects; See also: Titration, Amylin analog
Half-life also Elimination half-life: Half-life is the time it takes for the amount of a compound in the blood to fall by half. Atlas entries list the approximate elimination half-life because it sets dosing cadence: a half-life of minutes means several doses a day, one of about a week means weekly dosing. After about five half-lives roughly 97% of a dose has cleared, the window that matters for washouts, bloodwork and surgery.; In the atlas: Semaglutide, BPC-157; Read: The peptide atlas; See also: Steady state, Washout, PEGylation
HPG axis also HPTA, Hypothalamic-pituitary-gonadal axis: The HPG axis is the hypothalamic-pituitary-gonadal hormone chain: the hypothalamus releases GnRH, the pituitary answers with LH and FSH, and the testes or ovaries produce sex hormones and, in men, sperm. Rising testosterone or estrogen feeds back to slow the chain. That feedback is why anabolic steroids and most SARMs suppress natural testosterone and fertility, and what restart protocols try to reverse.; In the atlas: Gonadorelin (GnRH), Kisspeptin-10, HCG; Read: Gonadorelin (GnRH): A Tracking Guide for HPG Axis Support; See also: Post-cycle therapy (PCT), SERM, SARM
IGF-1 also Insulin-like growth factor 1: IGF-1 (insulin-like growth factor 1) is a hormone made mainly by the liver in response to growth hormone, and it carries out many of growth hormone's effects on muscle, bone and other tissue. Because growth hormone is released in brief pulses, serum IGF-1 is the standard blood test for following GH-raising compounds. IGF-1 LR3 and IGF-1 DES are modified synthetic variants of the hormone itself.; In the atlas: IGF-1 LR3, Somatropin (HGH); Read: Bloodwork During a Peptide Cycle: What to Watch; See also: GH secretagogue, Titration
Injection site rotation: Injection site rotation is the practice of moving each injection to a different spot instead of reusing the same one. Repeated injections in one place can cause lumps and scar tissue under the skin that make absorption less predictable. Common subcutaneous sites are the abdomen away from the navel, the outer thighs, the upper outer arms and the flanks. Logging the site of every dose makes rotation easy to follow.; Read: Subcutaneous vs Intramuscular: A Practical Comparison; See also: Subcutaneous (SC), Intramuscular (IM)
Insulin syringe units: Insulin syringe units are the markings on a U-100 insulin syringe, on which 100 units equal 1 ml, so one unit is 0.01 ml. They measure volume, not amount of compound: what one unit contains depends on the concentration after reconstitution. The same 250 mcg is 10 units from a 5 mg vial mixed with 2 ml of water, and 5 units if mixed with 1 ml. They are unrelated to international units (IU).; Read: How to Calculate Peptide Reconstitution: The Simple Math · Reconstitution calculator; See also: Reconstitution, Microgram (mcg) and milligram (mg), International unit (IU)
International unit (IU): An international unit (IU) is a measure of a substance's biological activity rather than its mass, defined separately for each substance against a reference standard. Somatropin (HGH), HCG and oxytocin are commonly dosed in IU. Because the definition differs from substance to substance, IU cannot be converted to milligrams without that substance's own conversion factor, and it has nothing to do with the unit markings on an insulin syringe.; In the atlas: Somatropin (HGH), HCG, Oxytocin; See also: Insulin syringe units, Microgram (mcg) and milligram (mg)
Intramuscular (IM): Intramuscular (IM) injection delivers a compound into muscle tissue, with a longer needle than subcutaneous injection, typically 1 to 1.5 inches. Muscle tolerates larger volumes, which is why oil-based steroid esters are usually injected IM while most peptides are given subcutaneously. The outer thigh and the deltoid are the sites usually described for self-injection, and IM technique carries more risk than subcutaneous injection without training.; In the atlas: Testosterone Cypionate; Read: Subcutaneous vs Intramuscular: A Practical Comparison; See also: Subcutaneous (SC), Ester, Injection site rotation
Intranasal: Intranasal administration delivers a compound as a spray or drops absorbed through the lining of the nose, avoiding both injection and digestion. In the atlas it is the typical route for small neuropeptides such as Semax, Selank and oxytocin, and the listed route for salmon calcitonin. Absorption is less complete and less consistent than with injection, and the amount delivered depends on spray technique.; In the atlas: Semax, Selank, Oxytocin; Read: Oxytocin: A Tracking Guide for a Social Neuropeptide; See also: Bioavailability, Subcutaneous (SC)
Lyophilized also Lyophilised, Freeze-dried: Lyophilized means freeze-dried: the peptide is frozen and its water removed under vacuum, leaving a dry powder or cake in a sealed vial. Most research peptides ship this way because the dry form is far more stable than a solution, keeping for long periods when stored cold and away from light. It must be reconstituted with a sterile liquid such as bacteriostatic water before injection, and the stability clock starts then.; Read: Peptide Storage 101: Lyophilized vs Reconstituted; See also: Reconstitution, Peptide stability
Microgram (mcg) and milligram (mg) also mcg, mg, µg: A milligram (mg) is one thousandth of a gram and a microgram (mcg, also written µg) is one thousandth of a milligram, so 1 mg equals 1,000 mcg. Peptide vials are usually labelled in milligrams while single doses are often discussed in micrograms, so converting correctly is the first step of reconstitution math: 250 mcg is 0.25 mg, one twentieth of a 5 mg vial.; Read: How to Calculate Peptide Reconstitution: The Simple Math · Reconstitution calculator; See also: Insulin syringe units, International unit (IU)
Off-label use: Off-label use is prescribing an approved drug for a condition, dose, age group or route that its official approval does not cover. It is legal for doctors in many countries and common in practice, but the evidence behind the approval does not directly support it. Several atlas compounds, including rapamycin, metformin and tesamorelin, are discussed mainly in off-label contexts such as longevity or body composition.; In the atlas: Rapamycin (Sirolimus), Metformin; Read: Rapamycin (Sirolimus): A Tracking Guide for an mTOR Inhibitor; See also: Clinical trial phases
PEGylation also PEGylated: PEGylation is the chemical attachment of polyethylene glycol (PEG) chains to a peptide or protein to extend how long it stays in the body. The larger molecule is cleared more slowly by the kidneys and resists breakdown by enzymes, so dosing can move from daily to weekly. It does not change what the molecule does at its receptor, and antibodies against PEG itself can develop with repeated exposure.; In the atlas: PEG-MGF; Read: PEGylated Peptides: What PEG- Means and Why It Changes Tracking; See also: Half-life, Steady state
Peptide: A peptide is a short chain of amino acids joined by peptide bonds; chains longer than roughly 50 amino acids are usually called proteins. Many hormones are peptides, including oxytocin and GLP-1, and most peptide drugs are injected because digestion breaks them down. The Peptid AI atlas also covers compounds that are not peptides, such as anabolic steroids, SARMs and small molecules, because they appear in the same protocols.; Read: The peptide atlas · Build Your First Peptide Protocol: A 5-Step Framework; See also: Bioavailability, Lyophilized
Peptide stability: Peptide stability is how long a peptide keeps its intended structure and potency before it degrades. Lyophilized powder stored frozen or refrigerated and out of the light stays stable for long periods; once reconstituted, most peptides are kept refrigerated and used within about 30 days. Heat, light, shaking, freezing a reconstituted vial and a contaminated stopper all speed degradation, and a cloudy solution is a sign to discard.; Read: Peptide Storage 101: Lyophilized vs Reconstituted · Bacteriostatic Water: Why It Matters and How to Use It; See also: Lyophilized, Reconstitution
Post-cycle therapy (PCT) also PCT: Post-cycle therapy (PCT) is a period after anabolic steroid or SARM use in which drugs are taken to help restart the body's own testosterone production, which the cycle suppressed. It typically relies on SERMs such as clomiphene, enclomiphene or tamoxifen, sometimes preceded by HCG, and is judged by follow-up bloodwork. The atlas treats an exit plan, PCT or ongoing medical replacement, as part of the decision to start.; In the atlas: Clomiphene (Clomid), Tamoxifen, Enclomiphene; Read: Clomiphene (Clomid): A Tracking Guide for the Fertility SERM; See also: HPG axis, SERM, SARM
Protocol: A protocol is the complete written plan for using a compound: the goal, route, dose range, dose frequency, cycle length, washout and what will be measured before, during and after. Writing it down before the first dose is what keeps the result interpretable. In Peptid AI the protocol is also the unit of tracking: every logged dose, reminder and journal entry attaches to one.; Read: Build Your First Peptide Protocol: A 5-Step Framework · Why Spreadsheets Fail for Peptide Protocols; See also: Cycle, Baseline, Titration
Reconstitution: Reconstitution is dissolving a lyophilized (freeze-dried) peptide in a sterile liquid, usually bacteriostatic water, so it can be drawn into a syringe. The volume of water added sets the concentration, which decides how many insulin syringe units hold a given dose. The water is run gently down the inside wall of the vial and swirled, never shaken, and the date is logged because the stability clock starts then.; Read: How to Calculate Peptide Reconstitution: The Simple Math · Bacteriostatic Water: Why It Matters and How to Use It · Reconstitution calculator; See also: Bacteriostatic water, Insulin syringe units, Lyophilized
Research chemical also Research use only, Not for human consumption: A research chemical is a compound sold for laboratory research, typically labelled "not for human consumption" or "research use only", that is not an approved medicine. It is not made or inspected under pharmaceutical quality rules, so its identity, purity and dose are unverified, and independent testing repeatedly finds mislabeled or contaminated products. Many peptides, SARMs and nootropics in the atlas reach consumers only this way.; In the atlas: MK-677, Ostarine (MK-2866); Read: MK-677 (Ibutamoren): A Tracking Guide for an Oral GH Secretagogue; See also: Certificate of analysis (COA), Clinical trial phases
SARM also Selective androgen receptor modulator: A SARM (selective androgen receptor modulator) is an oral compound designed to activate androgen receptors in muscle and bone while sparing tissues such as the prostate and skin. None is an approved medicine anywhere. Despite a "non-suppressive" reputation, most suppress natural testosterone, several are liver-toxic, and products are frequently mislabeled. Some compounds sold alongside them, such as MK-677 and cardarine, work by different mechanisms.; In the atlas: Ostarine (MK-2866), Ligandrol (LGD-4033), RAD-140 (Testolone); Read: Ostarine (MK-2866): A Tracking Guide for the Most-Studied SARM; See also: HPG axis, Post-cycle therapy (PCT), Research chemical
SERM also Selective estrogen receptor modulator: A SERM (selective estrogen receptor modulator) is a drug that blocks estrogen's effect in some tissues while mimicking it in others. Tamoxifen and raloxifene block estrogen at breast tissue; clomiphene and enclomiphene block it at the hypothalamus and pituitary, which raises LH and FSH and, in men, the body's own testosterone production. That second effect is why SERMs are the core of post-cycle therapy.; In the atlas: Tamoxifen, Clomiphene (Clomid), Raloxifene; Read: Tamoxifen: A Tracking Guide for the SERM; See also: Post-cycle therapy (PCT), Aromatase inhibitor (AI), HPG axis
Stack: A stack is two or more compounds run during the same period, each from its own vial and dosed separately, such as BPC-157 with TB-500. Unlike a blend, each one can be adjusted or stopped on its own. Stacking makes it harder to tell which compound caused an effect or a side effect, which is why the site's protocol guide suggests a single compound for a first cycle.; In the atlas: TB-500 + BPC-157 stack; Read: TB-500 + BPC-157: When to Stack and When to Cycle Separately · Build Your First Peptide Protocol: A 5-Step Framework; See also: Blend, Cycle
Steady state also Peak and trough: Steady state is the point during regular repeated dosing at which the amount of a compound eliminated between doses equals the amount taken in, so levels swing between the same high (peak) and low (trough) each interval instead of climbing. It is reached after roughly four to five half-lives, which is why a weekly long-acting compound can take a month or more to settle.; Read: PEGylated Peptides: What PEG- Means and Why It Changes Tracking · Exenatide (Byetta and Bydureon): Tracking the Original GLP-1; See also: Half-life, Titration
Subcutaneous (SC) also SubQ: Subcutaneous (SC or subQ) injection delivers a compound into the fat layer just under the skin, usually through a short insulin syringe needle of 6 to 8 mm. It is the default route for most peptides in the atlas, including BPC-157, ipamorelin and the GLP-1 agonists, because it is simpler and less painful than intramuscular injection and absorption is gradual. Volumes are typically under 1 ml.; In the atlas: BPC-157, Semaglutide; Read: Subcutaneous vs Intramuscular: A Practical Comparison; See also: Intramuscular (IM), Injection site rotation
Titration: Titration is raising a dose in planned steps over weeks rather than starting at the full amount, so the body adapts and side effects stay tolerable. It is standard for GLP-1 medicines, whose prescribing information steps the weekly dose up at intervals of about four weeks. The word is also used for adjusting a dose against bloodwork, as with growth hormone and IGF-1, or aromatase inhibitors and estradiol.; In the atlas: Semaglutide, Tirzepatide; Read: Tracking Semaglutide: Dose Titration and Side Effects; See also: GLP-1 receptor agonist, Protocol
Washout: A washout is a planned period without a compound after a cycle, long enough for it to leave the body and for measurements to show what persists and what reverts. Clearance takes about five half-lives, when roughly 97% of a dose is gone, so a washout runs from about a day for short-acting peptides to weeks for long-acting or PEGylated ones. It also keeps one experiment from blurring into the next.; Read: Build Your First Peptide Protocol: A 5-Step Framework · PEGylated Peptides: What PEG- Means and Why It Changes Tracking; See also: Half-life, Cycle, Baseline

Peptid AI is an educational and self-tracking tool — not a medical service, and not a vendor. Nothing here is medical advice, a prescription, or an endorsement. Doses reflect what is commonly reported in research literature; they are not recommendations. Many compounds listed are experimental, not approved for human use, and/or controlled substances that are illegal to possess without a prescription in many countries. Always consult a qualified physician before starting, changing, or stopping any protocol.