Peptide Glossary
Plain definitions for the 26 terms that actually come up when measuring, timing, and recording a routine — written to be useful rather than exhaustive.
Jump to: Measurement · Timing · Compounds · Administration
Measurement
Bacteriostatic water
Sterile water containing a preservative — typically 0.9% benzyl alcohol — which allows a reconstituted vial to be entered more than once. Distinct from plain sterile water, which contains no preservative. See how much to add.
Reconstitution
Dissolving a lyophilised (freeze-dried) powder in liquid to make it measurable. Reconstitution changes concentration, never the total amount in the vial. The reconstitution calculator handles the arithmetic.
Concentration
How much compound sits in a given volume of liquid, usually written mg/mL. Calculated as vial amount divided by water volume. Every unit count depends on it, which is why a unit figure is meaningless without the concentration it came from.
Unit
A graduation on an insulin syringe. On a standard U-100 syringe one unit is 0.01 mL. A unit measures volume, not amount — so the same unit mark holds different amounts at different concentrations.
U-100
An insulin syringe calibrated for 100 units per millilitre, making one unit 0.01 mL. The standard human insulin syringe and what nearly all peptide arithmetic assumes.
U-40
An insulin syringe calibrated for 40 units per millilitre, making one unit 0.025 mL — two and a half times a U-100 unit. Mostly veterinary. See U-100 vs U-40.
mcg and mg
Micrograms and milligrams. 1,000 mcg equals 1 mg. Mixing the two up is a 1,000-fold error, which is why most calculators ask you to state the unit explicitly rather than inferring it.
IU
International Unit — a measure of biological activity rather than mass. IU does not convert to milligrams by a universal factor; the ratio is compound-specific and has to come from the product documentation.
Lyophilised
Freeze-dried. Peptides are commonly supplied as a lyophilised powder for stability, and require reconstitution before they can be measured by volume.
Timing
Half-life
The time for the amount of a compound in the body to fall by half. A rate, not an expiry: after one half-life half remains, after two a quarter. See the half-life chart for 39 compounds.
Activity window
How long downstream effects are said to persist, which can be much longer than the half-life. A softer figure than an elimination half-life and worth treating with more caution.
Time to clear
Conventionally about five half-lives, at which point roughly 3% of the original amount remains. An estimate derived from a published figure, not a measurement of any individual.
Steady state
The point at which the amount entering matches the amount clearing, so levels stop climbing. Reached after roughly five half-lives of regular administration — days for short compounds, over a month for weekly ones.
Accumulation
What happens when the interval between administrations is shorter than the clearance time: each one lands on top of what remains. The reason a weekly compound's first month looks nothing like its third.
Titration
Adjusting an amount in steps over time rather than starting at a target. Relevant to recordkeeping because a log capturing only the first amount stops describing reality once steps begin.
Compounds
Peptide
A short chain of amino acids — shorter than a protein. Some compounds tracked alongside peptides are not peptides at all: MK-677 is a small molecule, for instance.
Secretagogue
A compound that prompts the body to release something it already makes, rather than supplying it directly. Growth hormone secretagogues act on the pituitary instead of introducing growth hormone.
GHRH analogue
A synthetic analogue of growth hormone-releasing hormone. CJC-1295 and sermorelin are examples. See growth hormone peptides.
GLP-1 agonist
A compound acting on the glucagon-like peptide-1 receptor. Semaglutide is the best known; dual and triple agonists such as tirzepatide act on additional receptors. See GLP-1 peptides.
DAC
Drug Affinity Complex — a modification binding a peptide to serum albumin so it clears far more slowly. CJC-1295 with DAC has a half-life around 8 days; without it, around 30 minutes.
Stack
Two or more compounds run in the same period. For recordkeeping the important point is that a stack is several separate series, not one — combining them into a single entry destroys the ability to read either back.
Cycle
A defined period of use followed by a break. Relevant to a log mainly because the boundaries need recording; a history without them is hard to interpret months later.
Administration
Subcutaneous
Into the fat layer beneath the skin, abbreviated SubQ or SC. The most common route for reconstituted peptides and the one insulin syringes are designed for.
Intramuscular
Into muscle tissue, abbreviated IM. Uses a longer needle than subcutaneous administration and is less common for peptides.
Site rotation
Varying where an injection is given rather than repeating one spot. Worth logging because the record is the only reliable way to know where the last several went.
Draw
Pulling liquid into the syringe. A draw is described in units or millilitres — both measures of volume — and only becomes an amount once concentration is known.
Put the terms to work
PepTrack keeps concentration, schedule, and history together so the vocabulary above turns into a record you can actually read back. Free on iPhone, no account required.
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