Peptide Glossary

May 9, 2026

Common terms you’ll see across peptide protocols and product descriptions.

Aspirate: Pulling back on the syringe plunger to check for blood before injecting. Standard for IM, not needed for subQ.
Bacteriostatic water (bac water): Sterile water with 0.9% benzyl alcohol added as a preservative. Standard solvent for reconstituting most peptides; allows ~28 days of refrigerated storage after mixing.
BDNF: Brain-derived neurotrophic factor. A protein critical for learning, memory, and neuroplasticity. Several peptides (Semax, Selank) elevate BDNF.
Bioregulator: Class of short peptides (2-4 amino acids) developed in Russian gerontology research. Tissue-specific signaling. Used in courses, not continuously. Examples: Epitalon, Cortagen.
Cycle: A period of taking a compound followed by a period off it. Most peptide protocols use 4-12 week cycles with 2-4 week breaks.
DAC: Drug Affinity Complex. A chemical modification (added to CJC-1295 with DAC) that binds the peptide to albumin and extends half-life from minutes to days.
Downregulation: The cellular response of pulling receptors off the surface when they’re overstimulated. Reduces a peptide’s effect. Cycling prevents this.
GHRH: Growth hormone releasing hormone. The body’s natural signal to release GH. Sermorelin, CJC-1295, and Tesamorelin are all GHRH analogs.
GHRP: Growth hormone releasing peptide. A class that mimics ghrelin to trigger GH release. Ipamorelin, GHRP-2, GHRP-6, Hexarelin.
GLP-1: Glucagon-like peptide 1. A gut hormone that slows digestion and increases satiety. The “GLP-1 drugs” (semaglutide, tirzepatide, retatrutide) all activate this receptor.
HGH / GH: Human growth hormone (somatropin). The actual hormone, vs. the secretagogues that stimulate its release.
IGF-1: Insulin-like growth factor 1. The downstream hormone GH causes the liver to produce. Most of GH’s effects are actually IGF-1’s effects.
IM: Intramuscular injection. Into muscle tissue. Used for some hormones, NAD+ at higher doses.
IU: International Unit. A measure of biological activity used for HCG, HMG, HGH. Not the same as mg or mcg.
Lyophilized: Freeze-dried. The state most peptides ship in — a small puck of powder at the bottom of the vial.
mcg / µg: Microgram. 1/1,000 of a milligram. Most peptide doses are in mcg.
Melanocortin receptors: MC1R, MC3R, MC4R, etc. Activated by Melanotan II and PT-141. MC1R drives skin tanning; MC4R drives sexual arousal pathways.
NNMT: Nicotinamide N-methyltransferase. An enzyme overexpressed in obese fat tissue. 5-Amino-1MQ inhibits it.
PCT: Post-cycle therapy. Protocols (typically HCG, SERMs) used to restore natural hormone production after androgen cycles.
Pulse: A discrete release event of a hormone. GH is normally released in pulses, especially during deep sleep. CJC + Ipa enhances pulse amplitude.
Reconstitution: Mixing lyophilized peptide powder with a sterile solvent (usually bac water) to create an injectable solution.
Receptor agonist: A compound that binds and activates a receptor (the natural signal does this). Most peptide drugs are agonists. Antagonists block.
Sharps container: Puncture-resistant container for used needles and syringes. Required for safe disposal.
SubQ / SC: Subcutaneous injection. Into the fat layer just below the skin, typically with an insulin syringe.
Stack: Running multiple compounds simultaneously, ideally with synergistic mechanisms.
Telomere / telomerase: Telomeres are the protective caps on chromosome ends; they shorten with each cell division. Telomerase is the enzyme that lengthens them. Epitalon research suggests telomerase activation.
Tonicity: How concentrated a solution is relative to body fluid. Isotonic = matches; hypertonic = saltier; hypotonic = more dilute. Hypertonic injections sting.
Titration: Gradually increasing dose over time, usually to manage side effects. Standard for GLP-1s.
U-100 syringe: Insulin syringe where 100 units = 1 mL. The standard for peptide subQ injection.

For pages where these come up in context, see the blog or the beginner’s guide.