Glossary

Plain definitions of the peptide and reconstitution terms used across PepDialed. Definitions only — this page does not give medical advice, recommend doses, or make efficacy claims.

Peptide

A short chain of amino acids — smaller than a protein. Research and pharmaceutical peptides range from a few to a few dozen amino acids.

Reconstitution

Mixing a lyophilized (freeze-dried) peptide powder with a sterile liquid — usually bacteriostatic water — to form a liquid solution. FDA-approved products come ready-to-use and are not reconstituted by the user.

Bacteriostatic water (BAC water)

Sterile water with 0.9% benzyl alcohol added to inhibit bacterial growth, commonly used to reconstitute lyophilized peptides. Distinct from plain sterile water for injection.

Lyophilized

Freeze-dried into a dry powder for stability and shipping. Lyophilized material must be reconstituted with a liquid before it can be drawn into a syringe.

Half-life

The time for the blood concentration of a substance to fall by half. It is a published pharmacology value for some peptides (e.g. ~7 days for semaglutide) and unknown/uncharacterized for many research peptides.

Subcutaneous (SubQ)

Into the fatty layer just beneath the skin — one common injection route. Neutral definition only; this glossary does not advise on technique or use.

International Unit (IU)

A unit of measure based on a substance's biological activity rather than its weight. Note that insulin-syringe markings labeled 'units' are a volume scale, not IU.

U-100 syringe

An insulin syringe whose barrel is calibrated so that 100 units = 1 mL (1 unit = 0.01 mL). This is the standard, most common insulin syringe.

U-40 syringe

An insulin syringe calibrated so that 40 units = 1 mL (1 unit = 0.025 mL). Less common than U-100 and used with U-40-concentration insulin; the markings are not interchangeable with U-100.

mg vs mcg

A milligram (mg) equals 1,000 micrograms (mcg). Peptide vials are usually labeled in mg, while amounts are often discussed in mcg — a factor-of-1,000 difference to keep straight.

GLP-1 receptor agonist

A class of compounds that activate the GLP-1 receptor (for example semaglutide and tirzepatide). Several members are FDA-approved prescription medicines.

Research use only (RUO)

Labeling indicating a material is sold for laboratory research, not for human use or as a medicine. RUO material is not an FDA-approved product.

FDA-approved

A product the FDA has reviewed and authorized for a specific medical use. This is distinct from unapproved, compounded, or research-grade compounds, which have not been through that review. FDA — Drug approvals

503A / 503B compounding

US regulatory categories for pharmacy compounding: 503A covers patient-specific prescriptions from traditional pharmacies; 503B covers registered outsourcing facilities. Which peptides may be compounded depends on FDA bulk-substance lists. FDA — human drug compounding (503A)

Amino acid

One of the small molecular building blocks that link together to form peptides and proteins. The specific sequence of amino acids defines a given peptide.

Peptide bond

The chemical bond that joins two amino acids together. A chain held together by peptide bonds is what makes something a peptide.

Concentration (mg/mL)

The amount of peptide dissolved per millilitre of reconstituted solution — for example, 5 mg of powder in 2 mL of liquid gives 2.5 mg/mL. It is simply the vial's peptide amount divided by the volume of liquid added, and it is what a reconstitution calculator computes.

Growth hormone secretagogue

A neutral class term for compounds that stimulate the body's release of growth hormone, including GHRH analogs and growth-hormone-releasing peptides (GHRPs). A category label only — not a statement of safety, efficacy, or approval.

GHRH (growth hormone-releasing hormone)

A hormone made in the hypothalamus that signals the pituitary gland to release growth hormone. Several research and pharmaceutical peptides are GHRH analogs — synthetic molecules that mimic this signal — for example sermorelin and tesamorelin. Definitional only; not a statement of safety, efficacy, or approval.

GIP receptor

The receptor for glucose-dependent insulinotropic polypeptide (GIP), one of the body's incretin hormones. It is a separate target from the GLP-1 receptor; some compounds are 'dual agonists' that act on both — for example tirzepatide. A mechanism definition only — not a statement of safety, efficacy, or approval.

Intramuscular (IM)

Into a muscle — one of the routes by which injectable substances can be administered, as distinct from subcutaneous (beneath the skin). Neutral definition only; this glossary does not advise on route or technique.

Incretin

A class of gut hormones — the two main ones are GLP-1 and GIP — that the body releases after eating and that influence insulin. Several peptides are built to mimic them: GLP-1 receptor agonists (such as semaglutide and liraglutide) and dual GLP-1/GIP agonists (such as tirzepatide). A category definition only — not a statement of safety, efficacy, or approval.

Melanocortin receptor

A family of cell receptors (MC1R–MC5R) involved in processes such as pigmentation and, via the MC3/MC4 receptors, sexual-response and appetite signalling. Some peptides act on this system — for example PT-141 (bremelanotide). A mechanism definition only — not a statement of safety, efficacy, dosing, or approval.

Net peptide content

The actual mass of pure peptide in a vial, which is usually less than the labelled milligrams because lyophilized peptide also contains counter-ions (often acetate salt) and bound water. It's a chemistry/quality concept, not a dosing instruction — it simply explains why a vial's true peptide amount can be a bit below the number on the label.