Reference
140 terms covering peptide biology, pharmacology, regulatory status, clinical research methodology, and common peptide classes — cross-linked to our compound, mechanism, and condition pages.
Pharmacology
24 terms
Biochemistry
46 terms
Regulatory
17 terms
Clinical
19 terms
Administration
15 terms
Research Methods
12 terms
Peptide Classes
7 terms
503A compounding pharmacies prepare customized medications for individual patients based on prescriber orders. They are regulated by state boards of pharmacy and must comply with USP standards.
Related: FDA Compounding Category 2
503B facilities are registered with the FDA and subject to cGMP standards. They can prepare office-stock compounded drugs without patient-specific prescriptions — unlike 503A pharmacies.
Related: 503A Pharmacy, Compounding Pharmacy
Adverse events are tracked in clinical trials and post-market surveillance. Serious adverse events (SAEs) are those causing hospitalization, disability, or death.
Related: Side Effect, Pharmacovigilance
An agonist binds and activates a receptor. Full agonists produce the maximum possible response; partial agonists produce a submaximal response even at full receptor occupancy.
Related: Antagonist, GPCR
Amino acids are organic molecules containing both an amine (-NH2) and a carboxyl (-COOH) group, plus a side chain that defines each residue. Twenty standard amino acids are encoded by the human genome; several non-standard amino acids also appear in peptides (e.g., D-amino acids, 2-aminoisobutyric acid in CJC-1295).
AMPK is activated when cellular ATP drops, shifting metabolism toward energy production, glucose uptake, and mitochondrial biogenesis. MOTS-c and other peptides activate AMPK to improve metabolic flexibility.
Related: mots-c, Mitochondria
Amylin acts at calcitonin and amylin receptors to reduce postprandial glucose and food intake. Pramlintide is an FDA-approved amylin analog. Dual GLP-1/amylin agonists are in clinical development.
Related: GLP-1 Agonist
Angiogenesis is the growth of new capillaries from existing vessels. Healing peptides (BPC-157, TB-500) promote angiogenesis to improve tissue repair. VEGF is the central signaling molecule.
Related: VEGF, bpc-157, tb-500
Antagonists occupy receptors without triggering a signal, preventing endogenous or exogenous agonists from binding. Rare in therapeutic peptide design but common in traditional pharmacology.
Apoptosis removes damaged or excess cells without triggering inflammation. Dysregulated apoptosis contributes to cancer (too little) and neurodegeneration (too much). Several peptide mechanisms include pro- or anti-apoptotic signaling.
Related: Senescence, Autophagy
Autophagy clears dysfunctional mitochondria and misfolded proteins. It is upregulated by fasting and AMPK activation; suppressed by mTOR and growth signaling. Considered a candidate longevity mechanism.
Related: mTOR, AMPK, Senescence
Bacteriostatic water inhibits bacterial growth, making reconstituted peptides stable for multi-dose use over several weeks under refrigeration.
Related: Reconstitution
BDNF is a neurotrophin that promotes neuronal growth, differentiation, and synaptic plasticity. Nootropic peptides (Semax, Selank) upregulate BDNF and NGF.
Related: semax, selank, Nootropic
Biased agonists preferentially activate G-protein or β-arrestin pathways downstream of a GPCR. This selectivity can improve efficacy-to-side-effect ratios in modern peptide design.
Binding affinity measures the strength of the receptor-ligand interaction. Lower Kd/Ki values indicate tighter binding. High affinity means less drug is needed to occupy receptors, but affinity alone does not predict efficacy.
Oral bioavailability of peptides is generally very low due to GI degradation. Subcutaneous injection bypasses this. Semaglutide tablets (Rybelsus) achieve oral bioavailability using an absorption-enhancer formulation.
Related: Half-Life, Subcutaneous Injection (SC)
Breakthrough designation grants intensive FDA guidance and eligibility for rolling review. It has been granted to several peptide drugs in oncology and metabolic disease.
Related: Fast Track, Orphan Drug
Under Section 503A, compounding pharmacies may only use bulk substances that are on the FDA's approved list or are the subject of an FDA-approved drug. The FDA maintains nomination and review lists for candidate bulk substances.
Related: Compounding Pharmacy, 503A Pharmacy, FDA Compounding Category 2
CVOTs enroll high-risk patients and assess major adverse cardiovascular events (MACE) over several years. SUSTAIN-6, LEADER, and SELECT established cardiovascular benefits of GLP-1 agonists.
Related: GLP-1 Agonist
ClinicalTrials.gov registration is a prerequisite for publication in most medical journals. Each record has an NCT number, which is the canonical trial identifier. Peptide trials — semaglutide, tirzepatide, retatrutide — all have NCT numbers.
Related: Phase 3 Trial, IND Application
Temperature excursions degrade peptide drugs. Semaglutide, tirzepatide, and most lyophilized peptides require 2–8°C storage before reconstitution. Reputable suppliers document cold-chain compliance.
Related: Storage Temperature, Lyophilized
Collagen synthesis declines with age and is central to wound healing and skin appearance. Copper peptides (GHK-Cu) upregulate collagen gene expression in fibroblasts and are used for this property in dermatology.
Related: Fibroblast, ghk-cu
Compounding pharmacies combine ingredients to create patient-specific medications. 503A pharmacies serve individual prescriptions; 503B outsourcing facilities serve larger healthcare institutions.
Related: 503A Pharmacy, FDA Compounding Category 2
A 95% confidence interval gives a plausible range for the true effect. Narrow intervals indicate precise estimates; wide intervals indicate uncertainty. CIs that include zero (for differences) or 1 (for ratios) indicate non-significance.
Related: P-value, Randomized Controlled Trial
Copper peptides deliver Cu²⁺ to cells, acting as signaling molecules for collagen synthesis, antioxidant defense, and tissue remodeling. GHK-Cu is the best-characterized.
Related: ghk-cu, Angiogenesis
Cortisol mobilizes glucose and suppresses inflammation but chronically elevated cortisol impairs immune function, sleep, and lean mass. Older GHRPs (hexarelin, GHRP-6) mildly raise cortisol; ipamorelin is selective and does not.
Related: ipamorelin, GHRP
Crossover designs improve statistical power by letting each subject serve as their own control. They require stable conditions and no carryover between treatments — making them unsuitable for interventions with lasting effects.
Related: Washout Period, Randomized Controlled Trial
Cyclic peptides resist proteolytic degradation better than linear peptides because their termini are not exposed to exopeptidases. Cyclization methods include disulfide bridges, head-to-tail amide bonds, and side-chain lactamization.
Related: Proteolysis, Peptide
Cytokines include interleukins, interferons, and TNFs. They coordinate inflammation, immunity, and tissue repair. Several peptide therapeutics (thymosin alpha-1) modulate cytokine profiles.
Related: Inflammation, Thymic Peptide
Most biological amino acids are the L-enantiomer. Incorporating D-amino acids into synthetic peptides slows proteolytic breakdown, extending half-life. CJC-1295 uses D-alanine to resist DPP-4 cleavage.
Related: Half-Life, Proteolysis, cjc-1295
Bacteriostatic water (containing 0.9% benzyl alcohol) is the standard diluent for multi-dose peptide reconstitution. Sterile water is used for single-use vials. Saline is less common for peptides but appropriate for some formulations.
Related: Reconstitution, Bacteriostatic Water, Lyophilized
Disulfide bonds form between the thiol groups of cysteine side chains. They are critical for the structural stability of peptides like oxytocin, vasopressin, and insulin. Disulfide scrambling during manufacturing is a common peptide-drug impurity concern.
Related: Amino Acid, Sequence
Double-blinding prevents expectation bias from affecting outcome measurement. It is considered standard for Phase 2 and Phase 3 trials of most interventions.
Related: Placebo, Randomized Controlled Trial
DPP-4 cleaves peptides at the N-terminal second position after proline or alanine. Native GLP-1 has a half-life of ~2 minutes due to DPP-4. GLP-1 analogs (semaglutide, liraglutide) are engineered to resist DPP-4 cleavage.
Related: GLP-1 Agonist, Proteolysis
EC50 is the half-maximal effective concentration in a functional assay. Reported in molar units (nM, pM). Lower EC50 = higher potency. Reported alongside IC50 for antagonists.
Efficacy describes the size of the pharmacological effect a drug is capable of. Two peptides can both be potent but differ in efficacy — e.g., a partial agonist may have high affinity but lower maximum effect than a full agonist.
Related: Potency, Partial Agonist, Agonist
Primary endpoints are pre-specified and determine trial success. Secondary endpoints are exploratory or hypothesis-generating. Composite endpoints combine related outcomes (e.g., MACE = major adverse cardiac events).
Related: Randomized Controlled Trial, Primary Endpoint
Fast Track allows more frequent FDA interaction and may permit rolling submission of NDA sections. It is less intensive than Breakthrough Therapy designation.
Related: Breakthrough Therapy, IND Application
In 2023, the FDA placed multiple peptides on the Compounding Category 2 list (substances that may not be compounded due to serious safety risks). This effectively restricted U.S. compounding pharmacy sales of BPC-157, CJC-1295, ipamorelin, and several others.
Related: 503A Pharmacy, RFK Jr. Reclassification
Fibroblasts secrete collagen, elastin, and growth factors during wound healing. They are central to skin biology and the target of most topical peptide cosmeceuticals.
Related: Collagen, ghk-cu
Gastroparesis is delayed gastric emptying. GLP-1 agonists delay emptying as part of their appetite-suppressive mechanism; pathological gastroparesis is rare but reported.
Related: GLP-1 Agonist
Growth hormone is released in pulses rather than continuously. Pulsatility is thought to be essential for healthy GH signaling; GHRH analogs and ghrelin agonists preserve it, while exogenous GH does not.
Related: GHRH Receptor, Ghrelin Receptor (GHSR-1a), Pituitary
Ghrelin stimulates appetite and growth hormone release via GHSR-1a. GHRPs and MK-677 mimic ghrelin at this receptor to trigger GH pulses (and sometimes appetite).
Related: Ghrelin Receptor (GHSR-1a), GHRP, mk-677
GHSR-1a is a class A GPCR expressed in the pituitary and hypothalamus. Ghrelin agonists like ipamorelin and MK-677 stimulate GH release through a pathway distinct from GHRH, producing additive effects when co-administered.
Related: GPCR, GHRH Receptor, GH Pulsatility
GHRH analogs bind the GHRH receptor in the pituitary to stimulate pulsatile endogenous GH release. They preserve hypothalamic feedback, unlike exogenous GH.
Related: GHRH Receptor, sermorelin, cjc-1295
GHRHR is a class B GPCR on pituitary somatotrophs. Activation stimulates synthesis and pulsatile release of growth hormone.
Related: GPCR, Pituitary, GH Pulsatility
GHRPs are synthetic ghrelin receptor agonists that stimulate GH release. They are often stacked with GHRH analogs for additive effects.
Related: Ghrelin Receptor (GHSR-1a), ipamorelin
GIPR is a class B GPCR for the incretin hormone GIP. Its co-activation with GLP-1R (as in tirzepatide) produces superior weight loss and glycemic control compared to GLP-1 monotherapy.
Related: GPCR, Incretin, GLP-1 Receptor
GLP-1 receptor agonists mimic the incretin hormone GLP-1. Approved examples include semaglutide, liraglutide, dulaglutide, and exenatide. Newer dual and triple agonists add activation of GIP and glucagon receptors.
Related: GLP-1 Receptor, semaglutide, Incretin
The GLP-1 receptor (GLP-1R) is a class B G-protein coupled receptor expressed in pancreatic beta cells, the hypothalamus, the gut, and the cardiovascular system. Activation triggers insulin release, suppresses glucagon, slows gastric emptying, and reduces appetite. It is the pharmacological target of the GLP-1 agonist class.
Related: GPCR, Incretin, GLP-1 Agonist
GLP-2 is co-secreted with GLP-1 from intestinal L-cells. Unlike GLP-1, its primary action is on intestinal mucosal growth. Teduglutide (a GLP-2 analog) is FDA-approved for short bowel syndrome.
Related: GLP-1 Agonist, Incretin
Glucagon mobilizes hepatic glucose via its own receptor. Triple agonists like retatrutide activate the glucagon receptor in addition to GLP-1 and GIP, contributing to increased energy expenditure.
Related: Glucagon Receptor, retatrutide
The glucagon receptor (GCGR) opposes insulin action by promoting hepatic glucose production and lipolysis. Triple agonists add glucagon receptor activation to increase energy expenditure and accelerate hepatic fat oxidation.
Related: triple-agonism, GPCR
cGMP (current GMP) standards govern facility cleanliness, documentation, testing, and batch release. Research-grade peptides sold "for research only" are not manufactured to GMP standards.
Related: Research Peptide, 503B Facility
G-protein coupled receptors are the largest family of membrane receptors in the human genome. They transduce signals from outside the cell (including peptide binding) into intracellular responses via Gαs, Gαi, Gαq, or G12/13 signaling.
Related: GLP-1 Receptor, GHRH Receptor, Melanocortin 4 Receptor (MC4R)
Half-life determines dosing frequency. Unmodified peptides usually have short half-lives (minutes to hours); modifications like PEGylation or fatty-acid conjugation (as in semaglutide) extend half-life to days.
Related: Pharmacokinetics (PK), semaglutide
HbA1c reflects average blood glucose over ~3 months. It is the primary endpoint in diabetes trials; GLP-1 agonists typically reduce HbA1c by 1-2.4 percentage points.
Related: GLP-1 Agonist, type-2-diabetes
HSDD is characterized by persistently reduced or absent sexual interest causing personal distress. PT-141 (bremelanotide) was approved for premenopausal HSDD in 2019.
Related: pt-141, Melanocortin 4 Receptor (MC4R)
The hypothalamus integrates endocrine and autonomic function. GLP-1 and melanocortin peptides act on hypothalamic circuits to modulate appetite and sexual behavior.
Related: Pituitary, GLP-1 Receptor, Melanocortin 4 Receptor (MC4R)
IC50 is used to characterize antagonists or enzyme inhibitors. Reported in molar units. Strong correlation with Ki when assay conditions are standardized.
Related: EC50, Antagonist
IGF-1 is the principal mediator of GH's downstream effects on growth, tissue repair, and metabolism. It is commonly measured to assess the biological impact of GH-stimulating peptides.
Related: GH Pulsatility, GHRH Receptor
Incretins are hormones released from the gut after eating that amplify insulin release from pancreatic beta cells. GLP-1 and GIP are the two principal incretins. Incretin-mimicking peptides form the basis of modern diabetes and obesity therapy.
Related: GLP-1 Receptor, GIP Receptor
An IND submission includes preclinical safety data, manufacturing information, and proposed trial protocols. The FDA has 30 days to place a clinical hold; if silent, the sponsor may proceed.
Related: NDA, Phase 1 Trial
Acute inflammation resolves; chronic low-grade inflammation underlies cardiovascular disease, metabolic disease, and aging. Several peptides are investigated for anti-inflammatory effects including BPC-157, thymosin alpha-1, and GLP-1 agonists.
Related: Cytokine, bpc-157
Repeated injection at the same site increases risk of lipohypertrophy, induration, and variable absorption. Abdomen, thigh, and upper buttock are commonly rotated for subcutaneous peptides. Leave at least a thumb's-width between adjacent injections.
Related: Subcutaneous Injection (SC), Adverse Event
Insulin sensitivity declines with age, obesity, and inactivity, contributing to type 2 diabetes. Peptides that improve insulin sensitivity (GLP-1 agonists, tesamorelin, MOTS-c) are studied in metabolic disease.
Related: GLP-1 Agonist, HbA1c, mots-c
Insulin syringes — typically 29–31 gauge — are the standard for subcutaneous peptide injection because the thin needle minimizes tissue trauma. 0.3 mL and 0.5 mL sizes with 0.01 mL graduations are most common.
Related: Subcutaneous Injection (SC), Reconstitution
Intent-to-treat (ITT) analysis preserves the benefits of randomization even when participants drop out or deviate from protocol. It is the primary analysis in most regulated trials and produces conservative effect estimates.
Related: Randomized Controlled Trial, Endpoint
IM injection provides faster absorption than SC but is more painful and requires proper technique to avoid nerves and vessels. Less commonly used for peptides.
Related: Subcutaneous Injection (SC)
Intranasal administration delivers peptides directly to the systemic circulation (or, for some peptides, to the CNS via the olfactory pathway). Semax and Selank are commonly administered this way.
Related: Bioavailability, semax
Leptin rises with fat mass and acts at hypothalamic receptors to suppress appetite. Obesity is typically a leptin-resistant state, so leptin supplementation alone has failed as a weight-loss therapy. GLP-1 drugs partially bypass this circuit.
Related: Ghrelin, Hypothalamus
In pharmacology, "ligand" is the general term for anything that docks into a receptor. Peptide drugs are ligands designed to mimic or block the endogenous ligand for a given receptor.
Related: Receptor, Agonist, Antagonist
Lipidation is the dominant half-life extension strategy for approved GLP-1 peptides. Liraglutide (C16 palmitoyl) and semaglutide (C18 fatty diacid) both exploit albumin binding to slow renal clearance from minutes to days.
Related: Half-Life, semaglutide
Lipodystrophy describes abnormal body-fat distribution. HIV-associated lipodystrophy (truncal fat accumulation) is the FDA-approved indication for tesamorelin.
Related: tesamorelin, Visceral Fat
Lyophilization removes water under vacuum at low temperature, producing a stable powder. Most peptide products are lyophilized and require reconstitution before injection.
Related: Reconstitution, Bacteriostatic Water
Macrophages shift between pro-inflammatory (M1) and resolving/repair (M2) phenotypes. This polarization is central to wound healing. Several peptides are studied for their effect on macrophage polarization.
Related: Inflammation, Cytokine
MASH (formerly NASH) is a progressive form of fatty liver disease featuring inflammation and fibrosis. Incretin peptides reduce MASH in clinical trials; retatrutide Phase II showed ~80% MASH resolution.
Related: fatty-liver-disease, retatrutide
MC4R is a melanocortin family GPCR expressed in the hypothalamus. Activation drives satiety, thermogenesis, and sexual arousal. PT-141 (bremelanotide) is an MC4R agonist approved for HSDD.
Related: GPCR, pt-141
The melanocortin system includes five receptors (MC1R–MC5R) and ligands derived from POMC. Targeting MC4R regulates appetite and sexual behavior; MC1R governs pigmentation. PT-141 and melanotan II act here.
Related: Melanocortin 4 Receptor (MC4R), pt-141, melanotan-ii
A meta-analysis pools data from multiple studies to estimate an overall effect size. When high-quality RCTs are combined, meta-analyses sit at the top of the evidence hierarchy.
Related: Randomized Controlled Trial, Systematic Review
Micrograms (mcg, μg) are standard units for peptide dosing, especially for GHRH and GHRP peptides (typical doses 100-300 mcg).
Related: Milligram (mg), Units (IU)
Milligrams are standard units for dosing GLP-1 agonists (semaglutide 0.25-2.4 mg weekly) and oral peptides like MK-677.
Related: Microgram (mcg), Units (IU)
Mitochondria are semi-autonomous organelles with their own genome. Mitochondrial-derived peptides (MDPs) like MOTS-c and humanin signal from mitochondria to the rest of the cell and are emerging longevity targets.
Related: mots-c, AMPK
MDPs are small peptides encoded in the mitochondrial genome. They signal between mitochondria and the rest of the cell, influencing metabolism and longevity.
Related: mots-c, AMPK
mTOR integrates nutrient, growth factor, and energy signals. Chronic mTOR activation accelerates aging in model organisms; its inhibition is a major longevity target. Peptides that affect insulin and IGF-1 signaling indirectly modulate mTOR.
NAD+ is a central coenzyme in metabolism. NAD+ levels decline with age; precursors like NR and NMN aim to restore the pool to support sirtuin-dependent longevity signaling.
Related: Sirtuin, Mitochondria
Nanomolar concentrations (10⁻⁹ M) are typical for peptide receptor affinity measurements. Binding affinity (Ki or Kd) is often in the low-nM range for therapeutic peptides.
Related: GPCR
An NDA includes complete clinical trial data, manufacturing specifications, and proposed labeling. Approval typically requires Phase 3 efficacy and safety data. Biologics use a parallel BLA (Biologics License Application) process.
Related: IND Application, Phase 3 Trial
Needle gauge is inversely related to diameter: a 31 G needle is thinner than a 25 G needle. Subcutaneous peptide injection typically uses 29–31 G needles, 4–12 mm long, for minimal discomfort.
Related: Insulin Syringe, Subcutaneous Injection (SC)
Nootropic peptides modulate cognition, memory, or attention. Semax and Selank are the best-known peptide examples, with BDNF upregulation and monoaminergic effects.
Related: semax, selank, BDNF
NNT is the reciprocal of the absolute risk reduction. Smaller NNT = more effective treatment. It gives a clinically interpretable sense of trial-effect magnitude that relative measures can obscure.
Related: Endpoint, Randomized Controlled Trial
Off-label prescribing is legal and common in the US — e.g., semaglutide for weight loss before 2021 approval. Off-label promotion by manufacturers is prohibited.
Related: NDA
Orphan drug designation provides tax credits, FDA fee waivers, and market exclusivity to encourage development for rare diseases. Tesamorelin originally pursued orphan status for HIV lipodystrophy.
Related: tesamorelin
Oxidative stress damages lipids, proteins, and DNA. It contributes to aging and a wide range of diseases. Peptides like MOTS-c and GHK-Cu have documented antioxidant effects in preclinical models.
Related: Mitochondria, mots-c
A p-value below a pre-specified threshold (typically 0.05) is the conventional marker of statistical significance. It does not measure effect size, clinical importance, or probability that the hypothesis is true.
Partial agonists have lower intrinsic activity than full agonists. Some GLP-1 and dual agonists are biased partial agonists, selectively activating certain downstream pathways.
Related: Agonist, Antagonist
PEGylation increases hydrodynamic radius, reduces renal clearance, and masks protease cleavage sites. It trades off potency for duration of action. Used in several long-acting biologic drugs but less common in currently-approved peptide drugs.
Related: Half-Life, Lipidation
A peptide is a molecule composed of two or more amino acids joined by peptide bonds. Peptides are smaller than proteins (typically under 50 amino acids) and act as hormones, signaling molecules, and enzyme regulators. Therapeutic peptides exploit this signaling role to produce clinical effects — for example, insulin (51 AAs) and semaglutide (31 AAs).
Related: Amino Acid, Protein, Polypeptide
Peptide bonds form during translation when ribosomes catalyze a condensation reaction between the carboxyl group of one amino acid and the amine group of the next, releasing water.
Related: Amino Acid, Peptide
PD describes drug effect in relation to concentration. For peptides, PD includes receptor affinity, downstream signaling, and tissue-specific response.
Related: Pharmacokinetics (PK), Half-Life
PK describes what the body does to a drug. Key parameters include half-life, bioavailability, volume of distribution, and clearance. Peptides typically have short plasma half-lives unless chemically modified.
Related: Half-Life, Bioavailability
Pharmacovigilance systems (e.g., FAERS in the U.S.) collect reports of adverse events after a drug reaches market, allowing detection of rare or long-latency safety signals.
Related: Adverse Event
Phase 1 trials establish tolerability, dose range, and PK/PD. They typically do not evaluate efficacy. Duration is weeks to months.
Related: Phase 2 Trial, Pharmacokinetics (PK)
Phase 2 establishes whether a drug has a meaningful clinical effect and selects doses for Phase 3. Common duration 3–12 months. Failure rate at Phase 2 is high.
Related: Phase 1 Trial, Phase 3 Trial
Phase 3 trials are typically randomized, controlled, and designed to meet FDA-specified endpoints. Success here is the basis for an NDA. Obesity trials like SURMOUNT-1 (tirzepatide) and STEP (semaglutide) are Phase 3.
Related: Phase 2 Trial, NDA
Phase 4 commitments are often required by the FDA as part of approval. They detect rare adverse events and confirm effectiveness in broader populations.
Related: Pharmacovigilance, Adverse Event
The pituitary gland secretes GH, TSH, ACTH, LH, FSH, and prolactin. GHRH analogs and ghrelin agonists target pituitary somatotrophs to release endogenous GH.
Related: GHRH Receptor, Ghrelin Receptor (GHSR-1a), GH Pulsatility
Placebos allow blinding and control for the expectation effect. Placebo-controlled trials are required for most drug approvals.
Related: Randomized Controlled Trial
Polypeptides are amino acid chains longer than typical peptides but folded into functional proteins. The distinction between "peptide" and "polypeptide" is semantic; most authorities use 50 amino acids as a soft cutoff.
Potency reflects how much of a compound is needed to elicit a given response. A more potent peptide achieves the same effect at a lower dose. Potency should not be confused with efficacy.
Related: Efficacy, EC50, Binding Affinity
Primary endpoints must be declared before the trial starts. Moving or adding endpoints after unblinding invalidates the result. FDA approvals typically hinge on primary endpoint success.
Related: Endpoint, Randomized Controlled Trial
Proteases (endopeptidases, exopeptidases) include DPP-4, neprilysin, trypsin, and chymotrypsin. Peptide drug design frequently targets resistance to specific proteases — e.g., semaglutide's acyl chain shields it from DPP-4.
Related: Proteolysis, DPP-4
Proteins are folded polypeptide chains, often over 100 amino acids, performing structural, enzymatic, and signaling roles. Growth hormone (191 AAs) is a protein; semaglutide (31 AAs) is a peptide.
Related: Peptide, Polypeptide
Most therapeutic peptides have short native half-lives because they are rapidly cleaved by serum and tissue proteases. Structural modifications — D-amino acids, PEGylation, lipidation — are used to slow proteolysis.
RCTs randomly allocate participants to minimize selection bias. They are the gold standard for establishing causation between an intervention and an outcome. Most peptide evidence levels depend on RCT availability.
Related: Meta-Analysis, Placebo
ROS are byproducts of mitochondrial respiration and immune activity. At low levels they serve as signaling molecules; at high levels they drive oxidative damage. Often abbreviated ROS.
Related: Oxidative Stress, Mitochondria
Receptors are the molecular targets of peptide drugs. Binding at a receptor — typically on the cell surface for peptides — initiates intracellular signaling cascades (e.g., cAMP, MAP kinase). Selectivity for a particular receptor subtype largely determines a peptide's effect profile.
Most peptides are shipped as lyophilized (freeze-dried) powders and must be reconstituted with bacteriostatic water before use. Our reconstitution calculator helps with volume and dosing calculations.
Related: Bacteriostatic Water, Lyophilized
REMS can include medication guides, prescriber training, patient registries, or restricted distribution. Several FDA-approved peptides (e.g., certain testosterone formulations, bremelanotide) carry REMS-adjacent labeling requirements.
Related: Pharmacovigilance, Adverse Event
Research peptides are sold under labels stating "not for human consumption." Their quality, purity, and labeling are not regulated as pharmaceuticals and should not be used as medications.
Related: FDA Compounding Category 2
In 2026, HHS under RFK Jr. moved 14 peptides off Category 2 and onto the FDA bulk substance eligibility list, restoring legal compounding access. This is a significant regulatory shift for the peptide industry.
Related: FDA Compounding Category 2, 503A Pharmacy
Cellular senescence is an irreversible arrest that accumulates with age, driven by telomere shortening, DNA damage, and oxidative stress. Senescent cells secrete inflammatory factors (SASP) that contribute to aging pathology.
Related: Telomerase, Mitochondria
The amino acid sequence defines the identity and function of a peptide. Sequences are written from N-terminus to C-terminus using either single-letter (HGEGTFTSDVSSYLEGQAAKEFIAWLVKGR) or three-letter abbreviations.
Related: Amino Acid, Peptide
Side effects are expected adverse effects based on a drug's mechanism. For GLP-1 agonists, common side effects include nausea, constipation, and injection-site reactions.
Related: Adverse Event
Sirtuins (SIRT1-SIRT7) deacetylate target proteins using NAD+ as a substrate. They regulate DNA repair, metabolism, and stress response — and are central to caloric-restriction and NAD+ longevity theories.
Related: NAD+
Somatotrophs are GH-producing cells in the anterior pituitary. They are the target of GHRH analogs and ghrelin agonists.
Related: Pituitary, GH Pulsatility
Stacking is common in peptide use — for example, CJC-1295 + ipamorelin for amplified GH release. Evidence for specific stacks varies; many combinations lack controlled study.
Related: cjc-1295, ipamorelin
Adult stem cells maintain tissue renewal — e.g., satellite cells in muscle, mesenchymal stem cells in bone marrow. Some peptide mechanisms (TB-500, thymosin peptides) involve stem-cell mobilization in preclinical models.
Related: tb-500, Thymic Peptide
Lyophilized peptides are often stable at room temperature for limited periods but should be refrigerated after reconstitution. Freezing reconstituted peptides can denature them. Manufacturer labeling gives the definitive storage window.
Related: Cold Chain, Lyophilized, Reconstitution
Subcutaneous fat accumulates beneath the skin and is less associated with cardiometabolic disease than visceral fat. Most peptide weight-loss therapies reduce both depots.
Related: Visceral Fat
Subcutaneous injection delivers peptides to the fatty layer beneath the skin for slow absorption into systemic circulation. Insulin, semaglutide, tirzepatide, and most research peptides use this route.
Related: Intramuscular Injection (IM), Intranasal
Systematic reviews follow predefined methods to identify, appraise, and synthesize all relevant studies. Unlike narrative reviews, they are reproducible and transparent.
Related: Meta-Analysis, Randomized Controlled Trial
Telomerase is a ribonucleoprotein enzyme (hTERT) that extends telomeres — the protective caps at chromosome ends. Telomere shortening is a hallmark of aging. Peptides like Epithalon upregulate telomerase expression in preclinical and pilot human studies.
Related: epithalon, Senescence
Thymic peptides originate from thymus-derived proteins and modulate T-cell maturation, immune response, and tissue repair. Thymosin Alpha-1 and Thymosin Beta-4 are the most clinically studied.
Related: thymosin-alpha-1, tb-500
Titration is standard for GLP-1 agonists — semaglutide starts at 0.25 mg/week and increases monthly to 2.4 mg/week. Gradual titration reduces GI side effects.
Related: semaglutide, Side Effect
International Units express dose based on biological activity rather than mass. GH is often dosed in IU; most peptides are dosed in micrograms or milligrams.
Related: Microgram (mcg), Milligram (mg)
VEGF is a family of signaling proteins that induce endothelial cell proliferation and new vessel formation. Peptides like BPC-157 upregulate VEGF at injury sites.
Related: Angiogenesis, bpc-157
Visceral adipose tissue surrounds abdominal organs and contributes disproportionately to cardiometabolic risk. Tesamorelin and incretin agonists preferentially reduce visceral depots.
Related: tesamorelin, Lipodystrophy
WADA publishes an annually updated Prohibited List. Peptide hormones (GH, GHRPs, GHRHs), growth factors, and — since 2022 — BPC-157 appear on this list. Athletes subject to testing must comply.
Related: GH Pulsatility
Washout duration is chosen based on drug half-life — typically at least 5× the half-life to ensure >96% clearance. Insufficient washout biases crossover results.
Related: Crossover Trial, Half-Life