Peptide Research Glossary

The building blocks of proteins and peptides. There are 20 standard amino acids. Peptides are chains of amino acids linked by peptide bonds. A dipeptide has 2 amino acids, a tripeptide has 3, and so on. Most research peptides contain between 2 and 100 amino acids.

Sterile water preserved with 0.9% benzyl alcohol, which inhibits bacterial growth in multi-use vials. The standard diluent for reconstituting peptides. Extends the shelf life of reconstituted peptides to approximately 4-6 weeks when refrigerated. Do not use regular sterile water — it has no preservative and allows bacterial growth.

A neurotrophin that supports neuronal survival, promotes synaptic plasticity, and drives neurogenesis. Low BDNF is associated with depression, cognitive decline, and neurodegeneration. Several nootropic peptides (Semax, P21) work primarily by upregulating BDNF expression.

The fraction of an administered dose that reaches systemic circulation unchanged. IV = 100%. SubQ peptides typically have 60-90% bioavailability. Oral peptides usually have very low bioavailability (<1-5%) because they are degraded in the GI tract — except for some that are engineered for oral use (semaglutide oral, MK-677).

A selective semipermeable border between the blood and the central nervous system that restricts passage of most substances. Most peptides cannot cross the BBB due to their size and polarity. Intranasal delivery bypasses the BBB via the olfactory nerve pathway, making it the preferred route for nootropic peptides.

Chemical Abstracts Service Registry Number — a unique numerical identifier assigned to every chemical compound. Used to unambiguously identify a specific chemical regardless of naming conventions. Example: BPC-157 CAS number is 137525-51-0. Useful for verifying that a vendor is supplying the correct compound.

A document from an accredited third-party laboratory certifying the identity, purity, and potency of a compound. For research peptides, a COA should confirm: correct compound identity (HPLC/MS analysis), purity ≥98%, and absence of contaminants. Always request a current COA from any peptide vendor.

The amount of peptide per unit volume of solution, expressed as mg/mL or mcg/mL. Calculated as: (vial size in mg) ÷ (mL of BAC water added). Example: 5mg vial + 1mL BAC water = 5mg/mL = 5000mcg/mL concentration.

A peptide analog modification where the sequence is reversed and all amino acids are replaced with their D-form (mirror image) counterparts. This renders the peptide nearly completely resistant to enzymatic degradation while preserving the 3D pharmacophore structure. FOXO4-DRI is an example.

A chemical modification on CJC-1295 that causes it to bind to albumin in the bloodstream, dramatically extending its half-life from ~30 minutes to ~8 days. CJC-1295 with DAC provides continuous GH elevation; without DAC (Mod GRF 1-29), it produces pulsatile GH release when co-administered with a GHRP.

Any compound that stimulates growth hormone secretion from the pituitary. Includes both GHRP-type compounds (act via ghrelin receptor) and GHRH-type compounds (act via GHRH receptor). MK-677 is an orally active, non-peptide GH secretagogue that mimics ghrelin.

A hypothalamic hormone that stimulates the pituitary to release growth hormone. Synthetic GHRH analogs (Sermorelin, CJC-1295, Tesamorelin) mimic this signal with extended half-lives. When combined with a GHRP, GHRH analogs amplify GH pulse amplitude synergistically.

A class of peptides that stimulate growth hormone release by binding to the ghrelin receptor (GHS-R1a) in the pituitary. Examples: Ipamorelin, GHRP-6, GHRP-2, Hexarelin. GHRPs work synergistically with GHRH analogs (like CJC-1295) to produce amplified GH pulses.

An incretin hormone secreted by intestinal K-cells that stimulates insulin secretion and adipogenesis. Tirzepatide is a dual GIP/GLP-1 agonist. GIP agonism amplifies the appetite-suppressing effects of GLP-1 through different signaling pathways in the hypothalamus.

A naturally occurring incretin hormone secreted by intestinal L-cells in response to food. Stimulates insulin secretion, suppresses glucagon, slows gastric emptying, and — most relevant for weight loss — activates GLP-1 receptors in the brain to reduce appetite. The target of semaglutide, tirzepatide, liraglutide, and retatrutide.

A compound that binds to and activates the GLP-1 receptor. The GLP-1 receptor is found in the pancreas, brain, gut, heart, and kidneys. Agonism produces insulin secretion, appetite suppression, gastric slowing, and cardiovascular protection. Class includes semaglutide, tirzepatide, liraglutide, retatrutide, and dulaglutide.

The time it takes for the concentration of a compound in the body to reduce by 50%. Determines dosing frequency. Peptides generally have short half-lives (minutes to hours) because they are degraded by peptidases. Modifications like PEGylation, albumin binding (e.g., semaglutide), or DAC attachment (CJC-1295) can dramatically extend half-life.

An analytical technique used to separate, identify, and quantify components in a mixture. For peptide testing, HPLC is used to determine purity (% of the sample that is the target compound) and to verify compound identity. Mass spectrometry (MS) is often combined with HPLC for definitive compound identification.

A hormone produced primarily in the liver in response to growth hormone. Directly stimulates muscle protein synthesis, cell growth, and tissue repair. The primary mediator of GH's anabolic effects. IGF-1 LR3 and IGF-1 DES are modified analogs with extended half-lives used in research.

Injection directly into muscle tissue. Produces faster absorption than subcutaneous due to higher vascularity. Used for some peptides including TB-500, certain IGF-1 variants, and Cerebrolysin. Typically administered into the deltoid, vastus lateralis, or gluteus.

Administration via nasal spray. Absorbed through the nasal mucosa and can cross directly into the CNS via the olfactory nerve pathway, bypassing the blood-brain barrier. Used for nootropic peptides (Semax, Selank), PT-141, and oxytocin. Typically 1-2 drops per nostril.

Direct injection into a vein, producing immediate systemic bioavailability (100%). Reserved for NAD+, Cerebrolysin, L-Glutathione, and other compounds requiring rapid systemic distribution. Requires sterile technique and is higher risk than SubQ.

Freeze-dried. Peptides are typically shipped as lyophilized (freeze-dried) white powder because this form is stable at room or refrigerator temperature for extended periods. Before use, lyophilized peptides must be reconstituted with bacteriostatic water or another appropriate solvent.

A class of neuropeptides derived from POMC (pro-opiomelanocortin) that bind to melanocortin receptors. MC1R activation stimulates melanin production (tanning). MC4R activation regulates sexual arousal and appetite. PT-141 and Melanotan 2 are melanocortin agonists targeting multiple MC receptors.

A protein (TGF-beta superfamily member) that inhibits muscle growth. Acts as a natural "brake" on muscle development. Peptides like Follistatin-344 and ACE-031 inhibit myostatin, effectively raising the ceiling for muscle mass. Loss-of-function mutations in myostatin produce extraordinary muscle development.

Addition of an acetyl group to the N-terminus of a peptide. This modification protects the peptide from N-terminal degradation by aminopeptidases, increasing its stability and potency. N-Acetyl Semax and N-Acetyl Selank are 2-3x more potent than their unmodified counterparts.

The process of attaching polyethylene glycol (PEG) chains to a peptide molecule. PEGylation increases molecular size, reduces immunogenicity, and dramatically extends half-life by reducing kidney filtration and peptidase degradation. PEG-MGF is the PEGylated version of Mechano Growth Factor.

A covalent chemical bond formed between the carboxyl group of one amino acid and the amino group of another. Forms the backbone of peptide and protein chains. Peptide bonds are hydrolyzed (cleaved) by peptidase enzymes, which is why most peptides have short half-lives and cannot be taken orally.

PubChem Compound Identifier — a unique integer assigned to every chemical compound in the NCBI PubChem database. Used to retrieve molecular structure images, physical properties, safety data, and bioactivity information. Can be used to verify compound identity and access scientific data.

The process of dissolving a lyophilized (freeze-dried) peptide powder in a liquid solvent — typically bacteriostatic water — to create an injectable solution. The ratio of peptide (mg) to solvent (mL) determines the concentration (mg/mL), which is then used to calculate injection volumes.

A compound that selectively induces apoptosis (programmed cell death) in senescent ("zombie") cells — cells that have stopped dividing but resist cell death and secrete inflammatory factors (SASP). Senescent cell accumulation is a hallmark of aging. FOXO4-DRI is a peptide senolytic.

An injection delivered into the layer of fat and connective tissue beneath the skin. The most common route for research peptides. Typically administered with a 28-31 gauge insulin syringe at a 45-90° angle. Provides steady, gradual absorption into the bloodstream.

An enzyme that extends telomeres — the protective caps on the ends of chromosomes that shorten with each cell division. Telomere shortening is considered a major driver of cellular aging. Epithalon (Epitalon) is the only peptide with human data demonstrating telomerase activation and measurable telomere lengthening.

The standard insulin syringe calibrated in units where 100 units = 1mL. The most common syringe for peptide injection. A dose of 10 units = 0.1mL. Needle gauges for SubQ injection typically range from 28G to 31G, with higher numbers being thinner.

International organization that sets the prohibited list for competitive sports. Many peptides are on the WADA prohibited list, including GH secretagogues (GHRPs, GHRH analogs), IGF-1 analogs, and others. Athletes subject to anti-doping rules should check the current WADA prohibited list before using any research peptide.