What's the difference between mcg and mg?

mg (milligram) and mcg (microgram) are both units of mass, but mg is 1,000 times larger. 1 mg equals 1,000 mcg. Peptide vials are usually labeled by total content in mg, but individual doses are almost always measured in mcg, so mixing the two up is one of the most common dosing mistakes.

What is bacteriostatic water used for?

Bacteriostatic water is sterile water with a small amount of preservative (usually benzyl alcohol) added. It's used to reconstitute lyophilized (freeze-dried) peptides into an injectable solution, and the preservative allows a single vial to be drawn from multiple times over its use period without bacterial growth, unlike plain sterile water.

What's the difference between GHRH and GHRP?

Both are classes of peptides that increase growth hormone release, but through different receptors. GHRH peptides, like CJC-1295 and Sermorelin, act on the GHRH receptor. GHRP peptides, like Ipamorelin, act on the ghrelin receptor instead. Because the pathways are different, GHRH and GHRP compounds are often stacked together on the theory that they produce a larger combined effect than either alone.

Why does peptide purity matter?

Purity describes what percentage of a vial's contents is actually the target peptide, as opposed to leftover solvents, synthesis byproducts, or other contaminants. Lower purity can mean a weaker or less predictable effect and introduces substances into the body that were never characterized. A Certificate of Analysis (COA) is how purity is verified for a given batch.

Is this glossary the same as the Peptide Encyclopedia?

No. The Peptide Encyclopedia covers individual compounds, like BPC-157 or CJC-1295, with the science, benefits, and research behind each one. This glossary covers the general vocabulary and units used around those compounds, like what mcg means, what reconstitution is, or what a COA verifies. The two are meant to be used together.

Peptide Glossary: Dosing, Injection & Regulatory Terms Explained

What This Glossary Covers

This page defines the vocabulary and units that show up across BioStackIQ's dosing guides, comparison articles, evidence reviews, and regulatory explainers, the kind of terms that get used constantly but rarely get their own explanation. It's a companion to the Peptide Encyclopedia, not a replacement for it: the Encyclopedia covers individual compounds like BPC-157 or CJC-1295, while this page covers the general terms used to talk about any of them, like what mcg means, what reconstitution is, or what a COA actually verifies.

Dosing & Measurement Preparation & Injection Mechanism & Biology Quality & Regulatory

Dosing & Measurement

mcg (microgram) #: One-millionth of a gram. The most common unit peptide doses are measured in.
mg (milligram) #: One-thousandth of a gram, equal to 1,000 mcg. Peptide vials are usually labeled by total content in mg, while individual doses are measured in mcg, which is one of the most common sources of dosing confusion. See the peptide dosage calculator for converting between the two.
mL (milliliter) #: A unit of liquid volume. mL measures how much liquid to draw into a syringe; it does not by itself tell you how much peptide that liquid contains, that depends on how the vial was reconstituted.
IU (International Unit) #: A standardized measure of biological activity rather than physical mass, used for a small number of compounds instead of mg or mcg. IU doses are not directly convertible to mg without knowing the specific compound's conversion factor.
Bioavailability #: The proportion of a compound that actually reaches systemic circulation and is able to have an effect. Bioavailability varies significantly by route of administration, which is a major reason most peptides are injected rather than taken orally.
Half-life #: The time it takes for a compound's concentration in the body to fall by half. A short half-life generally means more frequent dosing; a long half-life means less frequent dosing but a slower rise and fall in effect. See CJC-1295 With DAC vs Without DAC for a concrete example of how half-life changes a dosing schedule.
Pharmacokinetics #: How a compound moves through the body: absorption, distribution, metabolism, and elimination. Half-life and bioavailability are both pharmacokinetic properties.

Preparation & Injection

Lyophilized #: Freeze-dried. Research peptides ship as a lyophilized powder because it's far more stable than a liquid solution, and get reconstituted into a liquid only shortly before use.
Bacteriostatic water #: Sterile water with a small amount of preservative added, usually benzyl alcohol. It's used to reconstitute lyophilized peptides, and the preservative is what allows a single vial to be drawn from multiple times over its use period rather than needing to be used all at once.
Reconstitution #: The process of mixing a lyophilized peptide with a diluent, usually bacteriostatic water, to turn it back into an injectable liquid. See the peptide dosage calculator and reconstitution guide for the full step-by-step process.
SubQ (subcutaneous) injection #: Injection into the fatty tissue just beneath the skin. This is the most common injection method for research peptides, typically in the abdomen.
IM (intramuscular) injection #: Injection into muscle tissue, deeper than a subcutaneous injection. Less commonly used than subQ for most research peptides.

Mechanism & Biology

GHRH (growth hormone releasing hormone) #: A class of peptides that signal the pituitary gland to release growth hormone by acting on the GHRH receptor. CJC-1295 and Sermorelin are both GHRH analogs. See CJC-1295 vs Sermorelin for how two GHRH peptides can still differ significantly.
GHRP (growth hormone releasing peptide) #: A class of peptides that also stimulate growth hormone release, but through the ghrelin receptor instead of the GHRH receptor. Ipamorelin is the most commonly referenced example.
Secretagogue #: Any substance that prompts the body to release its own hormone, rather than supplying a synthetic version of that hormone directly. Both GHRH and GHRP peptides are growth hormone secretagogues.
IGF-1 (insulin-like growth factor 1) #: A hormone produced mainly in the liver in response to growth hormone. Because growth hormone itself is hard to measure reliably from a single blood draw, IGF-1 is commonly used as a downstream marker of GH-axis activity instead. See What Is IGF-1? Bloodwork & Peptides Explained.
GH pulse #: The burst-like pattern in which the body naturally releases growth hormone, mainly overnight, rather than a steady, continuous release. GHRH and GHRP peptides are generally discussed as amplifying these natural pulses rather than overriding the body's own rhythm.
Peptide sequence #: The specific order of amino acids that make up a peptide. The sequence determines the peptide's structure and function, and even a single amino acid change can produce a substantially different compound.

Quality & Regulatory

COA (Certificate of Analysis) #: A lab document verifying a specific peptide batch's purity and identity, typically produced using HPLC and mass spectrometry. See How to Read a Peptide COA for what to actually check on one.
Purity #: The percentage of a sample that is the target peptide itself, as opposed to residual solvents, synthesis byproducts, or other contaminants. Purity is what a COA is primarily used to verify.
503A #: The section of the Federal Food, Drug, and Cosmetic Act covering traditional pharmacy compounding. A peptide added to the FDA's 503A Bulk Drug Substances List may be legally compounded by a licensed 503A pharmacy. See What Is FDA's 503A Bulks List?.
Compounding pharmacy #: A pharmacy licensed to prepare customized medications, including certain peptides, under a valid prescription. See What Is a Compounded Peptide? for the full 503A vs 503B framework.

Looking for a specific compound instead of a general term? The Peptide Encyclopedia covers 21 individual compounds with their own science, benefits, and research pages.

Frequently Asked Questions

Disclaimer: This content is for informational purposes only and does not constitute medical or legal advice. Always consult a qualified healthcare provider before starting any peptide protocol.