Peptide Glossary
Plain-English definitions of every term you'll see in a peptide protocol — so you can read research papers, COAs, and dosing instructions with confidence.
Peptide
A short chain of amino acids (typically 2–50) that acts as a signaling molecule in the body. Larger chains are called proteins.
Reconstitution
Mixing a lyophilized (freeze-dried) peptide with a sterile liquid (usually bacteriostatic water) so it can be drawn into a syringe.
Bacteriostatic Water (BAC water)
Sterile water containing 0.9% benzyl alcohol. The alcohol inhibits bacterial growth so a vial can be used over multiple weeks.
mcg / mg
Micrograms and milligrams. 1 mg = 1,000 mcg. Most peptides are dosed in mcg; some larger ones (GLP-1s, retatrutide) in mg.
IU (International Unit)
Old labeling for insulin syringes. A U-100 syringe has 100 IU per 1 mL — every 10 'units' = 0.1 mL.
Subcutaneous (SubQ / SC)
Injection just under the skin into the fat layer — the most common research route for peptides. Typically uses a small 29–31g insulin syringe.
Intramuscular (IM)
Injection into a muscle. Used for some larger peptides; less common for short peptides.
Half-Life
The time it takes for half of a dose to be eliminated from the body. Determines how often you dose.
Lyophilized
Freeze-dried form of a peptide. Stable at room temperature for weeks; long-term storage should be cold.
GHRH / GHRP
Growth Hormone Releasing Hormone and Growth Hormone Releasing Peptide — two classes of compounds that stimulate the pituitary to release growth hormone.
GLP-1 / GIP / Glucagon Agonist
Receptor classes targeted by modern fat-loss peptides. Activating them suppresses appetite, slows gastric emptying, and improves glucose handling.
IGF-1
Insulin-Like Growth Factor 1. The downstream anabolic mediator of growth hormone. IGF-1 LR3 is a modified, long-acting form.
Cycle
A period of time you dose a peptide, followed by a break. Cycling helps maintain receptor sensitivity and is standard in long-running protocols.
Loading Dose
A higher-than-maintenance initial dose used in the first 1–2 weeks of a protocol to reach steady state faster.
Stack
Two or more peptides used together for a synergistic effect (e.g., BPC-157 + TB-500 for healing).
COA (Certificate of Analysis)
A lab report verifying the identity, purity, and quality of a peptide. Atlas Labs publishes a COA for every product.
HPLC
High-Performance Liquid Chromatography — the gold-standard test for measuring peptide purity. We require ≥99% HPLC purity.
Mass Spectrometry (MS)
Test that confirms a peptide's molecular weight matches its declared sequence.
Endotoxin
A toxin from the outer membrane of certain bacteria. Peptides intended for injection research should test low for endotoxin (LAL test).
Receptor Desensitization
When chronic dosing causes a receptor to respond less to the same signal. The reason most peptides are cycled.