Peptide Glossary: 120 Terms in Pharmacology, Dosing, and Safety

Pharmacology

25 terms in this category.

Agonist

A compound that binds to a receptor and activates it. Most peptide drugs are receptor agonists. Contrast antagonist.

Antagonist

A compound that binds to a receptor and blocks activation.

Partial agonist

A compound that binds and activates a receptor but with reduced maximal effect compared to a full agonist.

Inverse agonist

A compound that binds and produces the opposite biological effect of an agonist.

Receptor

A protein on or in a cell that recognizes a specific molecule and triggers a downstream signal.

GLP-1 receptor

The receptor activated by glucagon-like peptide-1 and by GLP-1 class drugs (semaglutide, tirzepatide, retatrutide).

Half-life

The time required for a compound's plasma concentration to fall by 50 percent. Semaglutide ~1 week, tirzepatide ~5 days, BPC-157 minutes.

Cmax

The peak plasma concentration of a compound after administration.

Tmax

The time after dosing at which Cmax is reached.

AUC

Area under the plasma concentration vs time curve. A measure of total drug exposure.

Bioavailability

The fraction of an administered dose that reaches systemic circulation unchanged.

First-pass metabolism

Hepatic metabolism that reduces oral drug bioavailability. Peptides are typically injected to bypass this.

Subcutaneous

Subcutaneous (subQ) injection delivers drug into the fatty layer just below the skin. The default route for most peptides.

Intramuscular

Intramuscular (IM) injection delivers drug into muscle tissue. Faster absorption than subQ.

Pharmacokinetics

Pharmacokinetics (PK) is the study of how a compound is absorbed, distributed, metabolized, and excreted.

Pharmacodynamics

Pharmacodynamics (PD) is the study of what a compound does to the body, including potency and effect duration.

Titration

Gradual dose escalation to minimize side effects. Standard for GLP-1 class drugs.

Steady state

The point at which drug input equals drug elimination, producing stable plasma levels. Typically reached after 4 to 5 half-lives.

Depot formation

Localized accumulation of injected drug that slowly releases over time, extending half-life.

Secretagogue

A compound that triggers release of an endogenous hormone. Ipamorelin is a GH secretagogue.

Analog

A structurally modified compound retaining the parent's core activity. Semaglutide is a GLP-1 analog.

Fragment

A truncated peptide retaining some activity of the parent. BPC-157 is a 15-amino-acid fragment of body protection compound.

kDa

Kilodalton, a molecular weight unit. Peptides are typically 1 to 5 kDa, proteins 10+ kDa.

Pulsatile

Pulsatile release means hormone is secreted in bursts (e.g., GH at night) rather than continuously.

Tachyphylaxis

Diminishing response to a drug after rapid repeated dosing. Mitigated by titration or cycling.

Dosing

20 terms in this category.

mcg

Microgram. 1,000 mcg = 1 mg. BPC-157 doses are usually 250 to 500 mcg.

mg

Milligram. 1 mg = 1,000 mcg. GH-axis peptides are usually 1 to 2 mg/day.

IU

International unit. A potency-based unit; conversion to mg varies by compound. Not interchangeable with syringe units.

U-100 syringe

A 100-unit insulin syringe. Each unit = 0.01 mL. The standard syringe for research peptide dosing.

U-40 syringe

A 40-unit insulin syringe (less common). Each unit = 0.025 mL.

U-500 syringe

A 500-unit syringe used for concentrated insulin. Not standard for peptide dosing.

Units

Syringe markings. Not interchangeable with IU. With a U-100 syringe, 1 unit = 0.01 mL of solution.

BID

Twice daily (bis in die). BPC-157 dosing is often BID.

QD

Once daily (quaque die). GHK-Cu is typically QD.

TIW

Three times weekly. CJC-1295/Ipamorelin sometimes dosed TIW.

QW

Once weekly. GLP-1 class drugs are typically QW.

Loading dose

A higher initial dose used to rapidly reach therapeutic concentrations. TB-500 protocols often use loading.

Maintenance dose

The ongoing lower dose used after loading or after titration is complete.

Titration ladder

A defined sequence of increasing weekly doses, used for GLP-1 class drugs to minimize GI side effects.

Cycle

A defined period of consecutive dosing followed by a break. Research compounds often cycled 4 to 8 weeks on, 4 to 8 weeks off.

On-cycle

Active dosing period.

Off-cycle

Rest period during which the compound is not administered.

Weeks per vial

A calculation: vial mg divided by weekly dose mg. Drives cost per month.

ED50

The dose producing 50 percent of maximal effect.

ED90

The dose producing 90 percent of maximal effect.

Reconstitution

15 terms in this category.

Bacteriostatic water

Bacteriostatic water for injection. Sterile water containing 0.9 percent benzyl alcohol as a preservative. Standard diluent for multi-use peptide vials.

Benzyl alcohol

The preservative in bacteriostatic water. Inhibits bacterial growth in multi-use vials.

Vial

A small glass bottle with a rubber stopper, sealed under vacuum. Most peptides ship as a lyophilized powder in vials.

Diluent

The liquid used to dissolve a lyophilized peptide. Bacteriostatic water is the standard diluent.

Reconstitution

The process of dissolving a lyophilized peptide in bacteriostatic water to create an injectable solution.

Swirl

Gentle agitation method used to mix peptide powder with diluent. Peptides should be swirled, not shaken, to preserve structure.

Recon volume

The volume of bacteriostatic water added to a vial. Determines concentration and units-per-vial math.

Units per vial

Calculated as (vial mg / dose per unit). With a 20 mg vial in 2 mL bac water, units-per-vial = 200.

27G needle

27-gauge syringe needle. Common for subQ peptide injection.

29G needle

29-gauge needle. Thinner than 27G; reduces injection-site discomfort.

31G needle

31-gauge needle. Among the thinnest available. Standard for insulin and increasingly for peptides.

Insulin syringe

A small-volume syringe (typically 0.3 to 1 mL) marked in U-100 units. Standard for research peptide dosing.

0.5 mL syringe

A 0.5 mL insulin syringe. Holds up to 50 units of solution.

1 mL syringe

A 1 mL insulin syringe. Holds up to 100 units of solution.

Lyophilized

Freeze-dried. Most peptide vials ship as a lyophilized powder cake that requires reconstitution.

Safety

25 terms in this category.

Adverse event

Adverse event (AE). Any unfavorable medical occurrence during drug use, whether causally related or not.

Serious adverse event

Serious adverse event (SAE). An AE that results in death, hospitalization, persistent disability, or is life-threatening.

CTCAE grading

Common Terminology Criteria for Adverse Events. A 5-grade severity scale (Grade 1 mild to Grade 5 death) used in oncology and increasingly in peptide trials.

Contraindication

A condition or factor that makes a drug inappropriate to use.

Absolute contraindication

A condition under which a drug must never be used. Example: Wilson disease for GHK-Cu.

Relative contraindication

A condition under which a drug should be used with caution or monitoring.

Black-box warning

The FDA's strongest prescription drug label warning. Tirzepatide and semaglutide both carry one for thyroid C-cell tumors.

Nausea

The reported adverse event with the highest incidence on GLP-1 class drugs (around 30 percent in Phase 3 trials).

Emesis

Vomiting. A frequent GI adverse event on GLP-1 class drugs.

Lipohypertrophy

Localized accumulation of fat at repeated injection sites. Mitigated by site rotation.

Injection-site reaction

Localized redness, itching, swelling, or pain at the injection site. The most common adverse event for non-GLP-1 research peptides.

Erythema

Redness of the skin, often at an injection site.

Pruritus

Itching, often at an injection site or as part of a systemic reaction.

Hypoglycemia

Low blood glucose. A risk on GLP-1 class drugs especially when combined with insulin or sulfonylureas.

Hyperglycemia

Elevated blood glucose.

Pancreatitis

Inflammation of the pancreas. A rare reported adverse event on GLP-1 class drugs.

Gastroparesis

Delayed gastric emptying. Reported with semaglutide, less common with tirzepatide.

MTC

Medullary thyroid carcinoma. A rare thyroid cancer linked to C-cell tumors. Black-box concern for GLP-1 class drugs.

MEN2

Multiple endocrine neoplasia type 2. A hereditary syndrome that includes risk of MTC. Absolute contraindication for tirzepatide and retatrutide.

Retinopathy

Damage to the retinal blood vessels. Risk in diabetics on GH-axis peptides; semaglutide also carries a documented retinopathy signal in SUSTAIN-6.

IGF-1

Insulin-like growth factor 1. Downstream marker of GH-axis activity. Elevated levels are monitored on CJC-1295/Ipamorelin protocols.

Water retention

Edema. A common reported effect on GH-axis peptides, typically transient.

Wilson disease

A genetic disorder of copper metabolism. Absolute contraindication for GHK-Cu and any copper-containing peptide.

Angiogenesis

Formation of new blood vessels. Pro-angiogenic activity in tissue-repair peptides raises a theoretical (not human-confirmed) tumor concern.

Pharmacovigilance

Ongoing safety monitoring of a drug after release. FDA-approved drugs report through MedWatch; research compounds rely on user-reported registries.

Regulatory

15 terms in this category.

FDA-approved

Cleared by the US Food and Drug Administration for a specific indication after Phase 3 trials. Examples: Mounjaro (tirzepatide), Ozempic (semaglutide).

Phase 1

First-in-human safety trials, typically n=20 to 100, healthy volunteers.

Phase 2

Dose-finding and efficacy trials, typically n=100 to 500, target population.

Phase 3

Pivotal efficacy and safety trials, typically n=1,000 to 10,000+. Required for FDA approval.

Phase 4

Post-marketing surveillance after a drug is approved.

IND

Investigational New Drug application. The FDA submission required to begin human trials.

NDA

New Drug Application. The FDA submission required for marketing approval.

503A

A US compounding pharmacy that prepares patient-specific compounded drugs. Was the source of compounded semaglutide during shortages.

503B

A US outsourcing facility that prepares larger-batch compounded drugs.

Research compound

A peptide intended for laboratory research only and not approved for human consumption. BPC-157, TB-500, KLOW Combo, MOTS-c, SLU-PP-332, and others fall in this category.

Prescription

Drugs that require a licensed prescriber's authorization. All FDA-approved peptides are prescription only.

COA

Certificate of Analysis. A document from an independent lab confirming the purity and identity of a peptide batch. Peptara publishes COAs on request.

HPLC

High-performance liquid chromatography. The standard purity test for peptides.

Mass spectrometry

Mass spectrometry. Confirms peptide identity by measuring molecular weight.

NMR

Nuclear magnetic resonance. Confirms peptide structure.

Mechanism

20 terms in this category.

GLP-1

Glucagon-like peptide-1. An endogenous incretin hormone that triggers insulin release, slows gastric emptying, and reduces appetite.

GIP

Glucose-dependent insulinotropic polypeptide. The second incretin hormone. Tirzepatide and retatrutide activate the GIP receptor in addition to GLP-1.

Glucagon

A pancreatic hormone that raises blood glucose. Retatrutide is a glucagon receptor agonist in addition to GLP-1 and GIP.

GH

Growth hormone. The pituitary hormone targeted indirectly by GH-axis peptides.

GHRH

Growth-hormone-releasing hormone. A hypothalamic peptide that triggers GH release. CJC-1295 is a GHRH analog.

GHRP

Growth-hormone-releasing peptide. A class of synthetic peptides that mimic ghrelin to trigger pulsatile GH release. Ipamorelin is a GHRP.

mTOR

Mechanistic target of rapamycin. A central regulator of cell growth and metabolism. Inhibition is linked to longevity research.

AMPK

AMP-activated protein kinase. A cellular energy sensor activated by exercise and by some peptides (notably MOTS-c).

Mitochondrial biogenesis

The formation of new mitochondria within cells. Driven by MOTS-c, exercise, and some pharmacological agents.

Thymosin beta-4

A 43-amino-acid peptide involved in actin sequestration, angiogenesis, and tissue repair. TB-500 is a synthetic fragment of thymosin beta-4.

BPC

Body Protection Compound. A 15-amino-acid peptide derived from human gastric juice, studied for tissue repair and gut healing.

Copper peptide

A peptide complexed with a copper ion. GHK-Cu is the canonical copper peptide used for skin and wound healing.

KPV

Lys-Pro-Val. A tripeptide with anti-inflammatory activity, included in the KLOW Combo blend.

Melanocortin

A class of peptide hormones (alpha-MSH, ACTH) that activate melanocortin receptors. PT-141 (bremelanotide) and MT-2 (melanotan-2) are melanocortin agonists.

BDNF

Brain-derived neurotrophic factor. A neuroplasticity protein elevated by some nootropic peptides (e.g., Semax).

VEGF

Vascular endothelial growth factor. A pro-angiogenic signaling protein upregulated by some tissue-repair peptides.

Nitric oxide

A vasodilatory signaling molecule involved in BPC-157's pro-angiogenic activity and in some vasodilator peptide effects.

Collagen synthesis

The cellular process of producing collagen. Upregulated by GHK-Cu and to a lesser extent by BPC-157.

Fibroblast

A connective-tissue cell that produces collagen and other extracellular matrix proteins. Targeted by GHK-Cu.

Incretin

A class of hormones (GLP-1, GIP) that trigger insulin release in response to nutrients. The GLP-1 class drug family is built on incretin biology.

Next steps

Educational only. Not medical advice. Glossary definitions are aggregated from peer-reviewed literature, trial registries, and FDA labeling. Consult a qualified healthcare provider before any peptide use.