Glossary
Plain-language definitions of the terms behind peptide, GLP-1, and TRT research — each one linked to the guide that covers it in depth.
Agonist
A compound that binds a receptor and switches it on, as opposed to an antagonist, which blocks it. A dual agonist activates two receptor types; a triple agonist, three.
Aromatase
The enzyme that converts androgens (like testosterone) into estrogens. Aromatase inhibitors such as anastrozole block this enzyme.
Bacteriostatic water
Sterile water containing about 0.9% benzyl alcohol, a growth-inhibiting preservative that lets a vial be entered repeatedly over days or weeks. It is the standard diluent for reconstituting multi-use peptide vials.
Concentration (mg/mL)
How much compound is dissolved per millilitre of liquid, computed as mass divided by volume. Concentration is the bridge between vial size and syringe units — the same dose is a different number of units at different concentrations.
DAC (Drug Affinity Complex)
A modification that binds a peptide to albumin in the blood, dramatically extending its half-life. CJC-1295 with DAC lasts days; the no-DAC form (mod GRF 1-29) lasts minutes.
Ester
A fatty-acid chain attached to a hormone (such as testosterone) that slows its release after injection. The ester length tunes the half-life; the body cleaves it to release the active hormone.
Ghrelin / GHS agonist
A peptide that activates the ghrelin (growth-hormone secretagogue) receptor — the other lever on the growth-hormone axis. Ipamorelin, GHRP-6, and GHRP-2 are GHS agonists.
GHRH analog
A peptide that mimics growth-hormone-releasing hormone and activates its receptor — one of the two levers on the growth-hormone axis. Sermorelin, CJC-1295, and tesamorelin are GHRH analogs.
GLP-1
Glucagon-like peptide-1, an incretin hormone released after eating that is involved in glucose regulation and satiety. GLP-1 receptor agonists like semaglutide activate its receptor.
Half-life
The time it takes for the amount of a compound in the body to decrease by 50%. After about five half-lives, roughly 97% of a single dose has cleared. Half-life largely determines how often a compound is dosed.
Incretin
A class of hormones (including GLP-1 and GIP) released by the gut after eating, involved in glucose regulation. The GLP-1 and dual-agonist compounds work by engaging incretin receptors.
International Unit (IU)
A unit that measures a substance by its biological activity rather than its weight, defined separately for each substance. There is no universal IU-to-mg conversion. HCG, for example, is dosed in IU.
Intramuscular (IM)
An injection placed into muscle. Muscle is more vascular than subcutaneous fat, so IM tends to absorb faster.
Lyophilized
Freeze-dried into a stable powder. Peptides are supplied lyophilized because the dry state stores and ships better than a solution; the end user reconstitutes it before use.
Peptide
A short chain of amino acids — the same building blocks as proteins, just fewer of them. Many of the body’s signalling molecules are peptides, which is why synthetic peptides are studied.
PK-PD disconnect
A mismatch between pharmacokinetics (how the blood level rises and falls) and pharmacodynamics (how long the effect lasts). BPC-157 is the classic example: a short serum half-life but longer-lasting effects in research models.
Read: BPC-157 half-life: why effects outlast the serum level →
Reconstitution
The process of adding a liquid (usually bacteriostatic water) to a lyophilized peptide so it can be measured and injected. The amount of liquid added sets the concentration, not the dose.
Secretagogue
Something that triggers the release of another substance. Growth-hormone secretagogues stimulate the growth-hormone axis, either as GHRH analogs or as ghrelin-receptor agonists.
Steady-state
The point during repeated dosing at which the amount entering the body each interval equals the amount clearing, so levels plateau. It takes roughly five half-lives of consistent dosing to reach.
Subcutaneous (SubQ)
An injection placed into the fat layer beneath the skin. Less vascular than muscle, so absorption is typically slower and steadier than intramuscular.
U-100
The designation for an insulin syringe that holds 100 units per millilitre, so 1 unit equals 0.01 mL. A syringe "unit" is a mark of volume, not an amount of drug.
Zyra Labs is a research and educational utility. Nothing on this page is medical advice, a dosing recommendation, or an endorsement of any compound. We never sell or source compounds and refuse sourcing questions. Consult a qualified clinician for decisions about your health.