Glossary: every term you'll see, explained

Every abbreviation, unit, and bit of jargon used across the site. Bookmark this.

Every abbreviation and bit of jargon you'll encounter on Pepdex. Grouped by what kind of thing it is. Bookmark and come back.

Units

mcg: Microgram. 1 mg = 1,000 mcg.; Microgram, the standard dose unit for most peptides. 1 milligram (mg) equals 1,000 micrograms (mcg). When a protocol says '250 mcg', that's 0.25 mg. Most peptide vials are dosed in mg total, but doses-per-injection are usually in mcg.
mg: Milligram. 1 mg = 1,000 mcg.; Milligram. The unit your peptide vial size is usually labeled in (e.g., 'BPC-157 5mg vial'). Doses are typically a fraction of that, expressed in mcg.

Delivery

Sub-q: Subcutaneous. Inject under the skin into the fat layer.; Subcutaneous injection. The needle goes into the fat layer just under the skin, not into muscle. Most peptides are sub-q. Common sites: lower abdomen (2 inches from the navel), love handles, outer thigh. Use a 29-31 gauge insulin syringe.
IM: Intramuscular. Injection into muscle.; Intramuscular injection. Deeper than sub-q, into the muscle tissue. Less common for peptides, more common for hormones. Uses a longer needle. TB-500 is sometimes given IM.
BAC water: Bacteriostatic water. Sterile water with 0.9% benzyl alcohol.; Bacteriostatic water. Sterile water mixed with 0.9% benzyl alcohol that prevents bacterial growth, letting you reuse the vial across multiple doses without contamination. This is what you mix lyophilized (freeze-dried) peptide powder with to reconstitute it.
Lyophilized: Freeze-dried powder form. Reconstitute before use.; Freeze-dried. The peptide is shipped as a fluffy white powder in a sealed vial, stable for months in the fridge or years in the freezer. To use it, you reconstitute (mix) with bacteriostatic water.
Reconstitution: Mixing dry peptide with BAC water to make it injectable.; The process of mixing a lyophilized peptide vial with bacteriostatic water so it becomes liquid and injectable. Done once per vial. See the Reconstitution guide for the step-by-step.
Insulin syringe: Tiny 29-31g needle; 1mL barrel = 100 'units'.; Standard insulin syringe. 1mL barrel total volume, marked in 100 'units' instead of mL — so 0.5mL = 50 units. The needle is 29-31 gauge, very thin, designed for sub-q injection. The Calculator converts your peptide dose into exact units to draw.

Schedule

EOD: Every other day.; Every other day. A common dosing frequency. Mon/Wed/Fri/Sun/Tue, etc. Used when daily would over-saturate the receptor or when the half-life is long enough to skip days.
Cycle: On-period of dosing followed by an off-period for receptor reset.; A defined on-period of dosing (e.g., 8 weeks) followed by an off-period (e.g., 4 weeks). Why: your receptors downregulate over time when constantly stimulated, so the same dose stops working. The break lets receptors upregulate back to baseline.
Loading phase: Higher / more frequent doses at the start of a cycle.; The opening 1-3 weeks of a cycle where doses are higher or more frequent than maintenance. Used to push tissue concentrations up faster. TB-500 and MT-1/2 are the classic examples.
Maintenance phase: Lower / less frequent doses to hold the effect.; The phase after loading where doses drop to a lower frequency or amount. Goal: hold the effect with less product and fewer side effects.
Titration: Slowly increasing dose over weeks to manage side effects.; Step-up dosing. Common with GLP/GIP class drugs (semaglutide, tirzepatide, retatrutide). You start at the lowest dose, hold it for 4 weeks, then increase if tolerated. Skipping titration spikes side effects badly.

Biology

Half-life: How long until 50% of a dose is cleared from your body.; The time it takes for half of a dose to be metabolized and cleared. Drives how often you dose. A 4-hour half-life peptide needs daily or twice-daily dosing; a 6-day half-life peptide is comfortably weekly. Steady-state (your level stops rising) is reached around 4-5 half-lives in.
GLP-1: Glucagon-like peptide-1 receptor. The main appetite-control receptor.; Glucagon-like peptide-1. A natural hormone your gut releases after eating that signals satiety to your brain. The 'GLP-1 drugs' (semaglutide, liraglutide) mimic and prolong this signal, suppressing appetite and slowing gastric emptying.
GIP: Second appetite-control receptor; Tirzepatide and Reta hit it.; Glucose-dependent insulinotropic polypeptide. A second appetite/insulin-related receptor. Adding GIP activation to GLP-1 (as Tirzepatide does) gives stronger weight-loss effect than GLP-1 alone.
DAC: Drug Affinity Complex. Extends a peptide's half-life dramatically.; Drug Affinity Complex. A modification that binds the peptide to albumin in your blood, dramatically extending half-life (CJC-1295 with DAC = ~8-day half-life vs ~30 min without). The 'no-DAC' version of CJC-1295 is the short-acting one used in peptide stacks.
Receptor downregulation: Receptors get less responsive when stimulated continuously.; When you stimulate a receptor too much for too long, your cells reduce the number of receptors or their sensitivity to compensate. This is why peptides need cycle breaks — your body adapts to the signal.
IGF-1: Insulin-like growth factor 1. Marker for GH-axis activity.; Insulin-like growth factor 1. The downstream hormone produced by your liver when GH hits it. Most GH effects are actually IGF-1 effects. Lab measurement of IGF-1 is the standard way to verify a GH-axis peptide is working.

Vendor

Vial: Sealed glass bottle holding the peptide.; The sealed glass bottle that ships from the vendor with peptide powder inside. Has a rubber septum top. You inject BAC water through the septum to reconstitute, then draw doses through the same septum.