Glossary
A quick reference for terms used throughout the site, useful to skim before reading the dosing or reconstitution guides if any of this is new to you.
Administration & Routes
Subcutaneous (SubQ / SC): Injection into the fat layer just under the skin, using a short, thin needle. This is how most peptides discussed on this site are administered.
Intramuscular (IM): Injection into muscle tissue, deeper than subcutaneous. Less common for peptides than for other injectables, though a small number of compounds are dosed this way.
Injection site: The physical spot on the body where an injection is given, commonly the abdomen or outer thigh for subcutaneous doses. Rotating sites rather than reusing the same spot helps avoid local irritation over time.
Units & Measurement
Microgram (mcg): The most common unit peptide doses are expressed in. One-thousandth of a milligram.
Milligram (mg): 1 mg = 1,000 mcg. Vials are typically labeled by total peptide content in mg, even when individual doses are measured in mcg.
International unit (IU): A measure of biological activity rather than weight, used for a small number of peptides with a pharmaceutical history (mainly growth hormone products). IU doesn’t convert to mcg/mg by a fixed ratio: it’s compound-specific.
Concentration: How much peptide is present per unit of liquid volume after reconstitution, usually expressed as mcg/mL. Concentration is what lets you convert a target dose into an actual injection volume.
U-100 syringe: A standard insulin syringe marked in “units,” where 100 units = 1 mL. Most peptide doses are drawn on a U-100 syringe. Some syringes are U-40 instead or marked directly in mL. Check the syringe itself rather than assuming.
Reconstitution & Storage
Lyophilized: Freeze-dried. The powder form most peptides ship in before being mixed into a liquid solution.
Bacteriostatic water (BAC water): Sterile water with a small amount of benzyl alcohol added as a preservative, used to reconstitute peptide powder so a vial can be used more than once without bacterial growth taking hold.
Reconstitution: The process of adding liquid (almost always bacteriostatic water) to freeze-dried peptide powder to turn it into an injectable solution. See the reconstitution guide for the full process.
Cold chain: Keeping a peptide consistently refrigerated (or frozen, before mixing), since heat, light, and repeated freeze-thaw cycles all tend to degrade peptides faster.
Protocol & Pharmacology
Half-life: The time it takes for half of a substance to be cleared from the body. A major factor in how often a given peptide needs to be dosed to maintain a steady effect.
Titration: Starting a protocol at a lower dose and increasing gradually based on individual response, rather than starting at the eventual target dose.
EOD (every other day): A dosing schedule that alternates between dosing days and off days, rather than dosing daily.
Cycling: Alternating a period of active use with a period off, as opposed to continuous, indefinite use.
Analog: A synthetic compound structurally similar to a naturally occurring one, designed to mimic or modify its effect.
Receptor agonist: A compound that binds to and activates a specific receptor, triggering the same response a naturally occurring molecule binding to that receptor would.
Stack: A combination of multiple peptides used together as part of one protocol. See Stacks for common examples.