Reference

Peptides and metabolic health glossary

Plain-English UK definitions for terms used across PeptideClear. Marked up with DefinedTermSet schema for AI search. 131 terms.

GLP-1: Glucagon-Like Peptide-1. A hormone the gut releases after eating. GLP-1 medications mimic this hormone to slow gastric emptying, increase insulin sensitivity, and reduce appetite.
GIP: Glucose-dependent Insulinotropic Polypeptide. A second gut hormone. Mounjaro is a dual GIP and GLP-1 agonist. Wegovy is GLP-1 only.
Tirzepatide: The active molecule in Mounjaro. A weekly injection developed by Eli Lilly. Approved in the UK for type 2 diabetes (2022) and weight management (2024).
Semaglutide: The active molecule in Wegovy and Ozempic. A weekly injection developed by Novo Nordisk. Wegovy is the weight-management licensed product in the UK; Ozempic is the diabetes brand of the same molecule at lower doses.
NICE TA1026: NICE Technology Appraisal 1026. The 2024 NICE guidance on tirzepatide for managing overweight and obesity. Defines the BMI thresholds, comorbidity requirements, and ethnicity-adjusted thresholds for NHS access.
Cohort 1 and 2: The first two published phases of NHS England Mounjaro access. Cohort 1 (BMI 40+, 4+ comorbidities) live since June 2025. Cohort 2 (BMI 35 to 39.9, 4+ comorbidities) launches 23 June 2026. Later cohorts extend eligibility progressively over up to 12 years; criteria for phases beyond June 2026 have not yet been finalised by NHS England.
NHS Cohort 1: BMI 40+ (37.5+ ethnicity-adjusted), 4 or more weight-related comorbidities. Live since June 2025.
NHS Cohort 2: BMI 35 to 39.9 (32.5+ ethnicity-adjusted), 4 or more weight-related comorbidities. Launches 23 June 2026.
NHS cohorts beyond June 2026: NHS England extends Mounjaro eligibility progressively in later phases after Cohort 2, prioritised by clinical need, over a period of up to 12 years. The criteria and timing for these later cohorts have not yet been finalised by NHS England.
ICB: Integrated Care Board. The 42 NHS England regional bodies that commission services in their area. Mounjaro rollout pace varies by ICB.
QOF: Quality and Outcomes Framework. NHS England primary-care contract framework. April 2026 update added GLP-1-relevant indicators.
Aftercare: Maintenance phase after reaching goal weight on a GLP-1. 82% regain at least 25% of lost weight within 12 months of stopping (Oxford analysis, January 2026).
High-touch route: Private clinic with app, coach, monthly check-in. Numan, Voy, Manual, Juniper. £200 to £300 per month.
Low-touch route: Online pharmacy with questionnaire then ship. Phlo, Pharmacy2U, SimplyMeds, Boots Online Doctor, Asda Online Doctor. £150 to £200 per month.
Maintenance dose: A continued lower or steady GLP-1 dose at goal weight, intended to prevent regain rather than drive further loss. Some clinics offer this; pharmacy-direct routes typically do not.
GLP-1 face: Colloquial term for facial volume loss after rapid weight loss on GLP-1. Mechanism is normal facial fat reduction; effect is more pronounced after age 35 because skin elasticity has declined.
SURMOUNT-1: The pivotal Eli Lilly tirzepatide trial. 72 weeks, average 22% weight loss at maximum dose.
STEP-1: The pivotal Novo Nordisk semaglutide trial. 68 weeks, average 15% weight loss at maximum dose.
SELECT: The Wegovy cardiovascular outcomes trial. Showed 20% reduction in major cardiovascular events. Underpins the July 2024 UK CV indication.
GHK-Cu: Glycyl-histidyl-lysine bound to copper. The most studied cosmetic peptide. Discovered by Pickart 1973. Used in serums for collagen support, barrier repair, skin firming.
Matrixyl 3000: A branded blend by Sederma combining palmitoyl tripeptide-1 and palmitoyl tetrapeptide-7. Most commercially recognised cosmetic peptide complex.
Argireline: Acetyl hexapeptide-8. Cosmetic peptide marketed for fine line reduction by inhibiting muscle contraction at the skin surface. Topical only.
INCI: International Nomenclature of Cosmetic Ingredients. The standardised ingredient list on every cosmetic product. Ingredient position correlates loosely with concentration.
Palmitoyl tripeptide-1: A signal peptide. One of the two peptides in Matrixyl 3000. Stimulates collagen and glycosaminoglycan synthesis in skin.
Palmitoyl tetrapeptide-7: A signal peptide. The second peptide in Matrixyl 3000. Reduces inflammation by limiting interleukin-6 production.
Snail mucin: Snail secretion filtrate. K-beauty staple, often paired with peptides. Hydrating and barrier-supportive.
Hydrolysed collagen: Collagen broken down (typically by enzymes) into smaller peptides for better gut absorption. Most marketed at 3 to 6 kDa molecular weight.
Type I collagen: The main collagen type in skin, hair, nails, tendons, and bone. Marine collagen is mostly Type I. Bovine collagen is Type I and III combined.
Type II collagen: The main collagen type in cartilage. Sourced from chicken sternum. Dosed in milligrams (40 mg undenatured / UC-II) not grams. Different absorption profile from Type I.
Type III collagen: The collagen type in skin elasticity, gut lining, and blood vessels. Almost always present alongside Type I in bovine collagen.
UC-II: Undenatured Type II collagen. The form retained from chicken cartilage that preserves immune-modulating activity. Used at 40 mg/day for joint support.
Marine collagen: Collagen sourced from fish skin and scales. Almost entirely Type I. Smallest molecular weight typically (1 to 3 kDa). Strong absorption.
Bovine collagen: Collagen sourced from cow hide. Type I + III combined. Most affordable per gram. Standard for skin and gut goals.
Vegan collagen: Misnomer. No plant supplement contains collagen. "Vegan collagen" products contain amino acid precursors (lysine, proline, glycine) plus vitamin C and assume your body builds collagen from them.
kDa: Kilodalton. Unit of molecular weight. Hydrolysed collagen at 3 to 6 kDa is small enough for efficient gut absorption.
Bolke 2019: Industry-funded RCT showing skin elasticity improvement with 10 g/day hydrolysed collagen over 90 days. Among the trials supporting collagen efficacy.
Choi 2019: Systematic review of 11 collagen RCTs concluding short-term effects on skin elasticity and hydration. Industry funding declared in source studies.
Shaw 2017: RCT showing 15 g hydrolysed collagen + 50 mg vitamin C, 60 minutes pre-exercise, doubled collagen synthesis at the tendon. The protocol behind tendon-recovery dosing.
BPC-157: Body Protection Compound 157. Synthetic peptide derived from a protein found in human gastric juice. Animal data only, no human RCTs. Sold under "research use only" framing in the UK.
TB-500: Synthetic fragment of thymosin beta-4. Research peptide with rodent data on tissue repair and anti-inflammatory effects. No published human RCTs. UK regulatory status same as BPC-157.
MOTS-c: Mitochondrial Open Reading frame of the Twelve S rRNA-c. Mitochondrial-derived peptide with mouse data on metabolic regulation and late-life intervention.
Ipamorelin: Growth-hormone secretagogue developed by Novo Nordisk. Phase II discontinued for postoperative ileus. No marketing authorisation. Research use only in the UK.
Tesamorelin: Growth-hormone-releasing-hormone analogue. The only peptide on this list with an FDA approval (HIV-associated lipodystrophy, EGRIFTA WR). Not NHS-prescribed. Research use only via UK retailers.
CoA: Certificate of Analysis. Document from a third-party lab confirming purity and identity of a chemical sample. Not a sterility certificate. Not a biological-activity certificate.
HPLC: High-Performance Liquid Chromatography. Lab technique that separates the components of a sample by chemical property. Used to measure peptide purity. Does not prove biological activity.
Mass spectrometry: Lab technique that identifies a molecule by its mass-to-charge ratio. Used alongside HPLC to confirm the named peptide is what is in the vial. Stronger than HPLC alone.
Research use only: The UK regulatory framing under which research peptides are sold. Products are marketed without health claims, not for human or animal consumption, sitting outside the medicines regulatory tier.
WADA: World Anti-Doping Agency. Maintains the prohibited list for tested athletes. Several research peptides (BPC-157, TB-500, MOTS-c, ipamorelin) are on it.
GPhC: General Pharmaceutical Council. The UK regulator of pharmacies and pharmacists. A legitimate UK online pharmacy holds a GPhC registration number.
POM: Prescription Only Medicine. Cannot be sold or dispensed without a prescription from a qualified prescriber. All GLP-1 weight management medications in the UK are POM.
MHRA: Medicines and Healthcare products Regulatory Agency. UK medicines regulator. Issues marketing authorisations and enforces against unlicensed medicinal products.
MHRA Yellow Card: The UK system for reporting adverse drug reactions. Anyone can submit a report at yellowcard.mhra.gov.uk.
ASA: Advertising Standards Authority. UK regulator of advertising. Issued enforcement notice on consumer-facing GLP-1 advertising in September 2025.
CAP code: Committee of Advertising Practice code. The set of rules ASA enforces. Restricts advertising of POM products to the public.
PIL: Patient Information Leaflet. The leaflet inside every UK medication box. The authoritative source on dosing, side effects, and missed-dose advice.
BNF: British National Formulary. The UK reference for prescribers on medicines, doses, and indications. Authoritative on every licensed UK medicine.
Medicines Act 1968: The primary UK statute governing the sale and supply of medicines. Sets the framework for what counts as a medicinal product.
Human Medicines Regulations 2012: The implementing regulations under the Medicines Act 1968. Day-to-day rules on UK medicines, including advertising, supply, and licensing.
Misuse of Drugs Act 1971: Controls drugs of abuse in the UK. Most research peptides are NOT controlled under this act.
Psychoactive Substances Act 2016: Bans novel psychoactive substances. Research peptides are NOT scheduled under this act.
Ethnicity-adjusted BMI: NICE-recommended BMI threshold reduction of 2.5 kg/m² for South Asian, Chinese, Black African, and African-Caribbean populations, reflecting higher metabolic risk at lower BMI.
Comorbidity: A weight-related health condition that counts toward NICE TA1026 eligibility. Includes type 2 diabetes, hypertension, dyslipidaemia, sleep apnoea, cardiovascular disease.
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Mounjaro KwikPen: Eli Lilly's multi-dose pre-filled pen device for tirzepatide. UK rollout from 2024. Replaces single-use vials with a 4-dose pen.
Dose titration: The structured ramp-up from starting dose to maintenance dose. Mounjaro typically titrates monthly: 2.5 mg, 5 mg, 7.5 mg, 10 mg, 12.5 mg, 15 mg.
Stopping rule (NHS): NICE TA1026 continuation criterion. Patients must achieve at least 5 percent weight loss from baseline by month 6 for NHS Mounjaro to continue.
Plateau: Period of stalled weight loss on a GLP-1 despite continued use at the same dose. Common at 9 to 12 months. Prescriber options: hold, titrate, or maintenance pivot.
Cohort: Phased rollout group in the NHS Mounjaro plan. Cohort 1 (BMI 40+, 4+ comorbidities) live since June 2025. Cohort 2 June 2026. Later cohorts extend eligibility progressively over up to 12 years; criteria beyond June 2026 have not yet been finalised by NHS England.
TA875: NICE Technology Appraisal 875 (March 2023). The NHS appraisal of semaglutide for weight management (the separate pathway from tirzepatide weight management TA1026).
TA664: NICE Technology Appraisal 664. The 2017 NHS approval of liraglutide (Saxenda) for weight management. Largely superseded by Mounjaro and Wegovy in 2024 to 2025 prescribing.
SmPC: Summary of Product Characteristics. The detailed prescriber-facing document on a UK licensed medicine. Authoritative on indication, dosing, contraindications, side effects.
SELECT trial: The Novo Nordisk semaglutide cardiovascular outcomes trial. 17,604 participants over 5 years. 20% reduction in major cardiovascular events. Underpins July 2024 UK CV indication.
SURMOUNT-4: Eli Lilly tirzepatide trial on weight maintenance after initial loss. Demonstrated continued use maintains loss; discontinuation drives regain.
REDEFINE: Novo Nordisk semaglutide trial published December 2025. Compared higher-dose semaglutide outcomes.
STEP-3: Novo Nordisk semaglutide trial with intensive behavioural therapy added to medication. Demonstrated additive effect of structured coaching alongside the drug.
C-cell hyperplasia: Thyroid C-cell proliferation observed in rodent studies with GLP-1 agonists. Drives the boxed warning against use in patients with personal or family history of medullary thyroid carcinoma or MEN 2.
Gastroparesis: Delayed gastric emptying. Already a feature of how GLP-1 medications work; can become clinically problematic at higher doses or in susceptible patients.
Compounded GLP-1: Custom-mixed semaglutide or tirzepatide from non-licensed sources. Common in the US through 2024. Not legal for routine UK supply. MHRA enforcement focus.
Bariatric pathway: The NHS surgical route (gastric sleeve, gastric bypass) for severe obesity. GLP-1 access (NICE TA1026) does not exclude future bariatric referral.
Specialist Weight Management Service (SWMS): NHS tier-3 service providing multi-disciplinary support for severe obesity. The commissioning route through which NHS Mounjaro is delivered in most ICBs.
Acetyl tetrapeptide-9: A cosmetic peptide marketed in some UK serums for collagen-supportive effect. Less commercially recognised than Matrixyl 3000 or GHK-Cu.
Acetyl octapeptide-3: Marketed as SNAP-8. Cosmetic peptide positioned as a longer-chain Argireline alternative.
Acetyl dipeptide-3 aminohexanoate: Marketed in some lash-growth serums under "peptide" claims. Disputed efficacy.
Stratum corneum: The outermost skin layer (15 to 20 cells thick). The barrier topical peptides must cross to reach the dermis.
Transepidermal water loss (TEWL): Rate of water loss through skin. A common skin-barrier integrity measure in cosmetic trials.
Fibroblast: Dermal cell that produces collagen and extracellular matrix. The target cell type for topical peptide signalling.
Elastin: Skin protein responsible for elastic recoil. Decline with age contributes to skin laxity. Topical peptides have mixed evidence for elastin synthesis.
Glycosaminoglycan (GAG): Long unbranched polysaccharide. Includes hyaluronic acid. Component of skin extracellular matrix that peptides can upregulate.
Niacinamide: Vitamin B3. The cosmetic peptide stack-mate that is most reliably compatible across formulations and pH.
Peptide-retinoid stacking: Using a peptide serum and a retinoid (retinol, retinaldehyde, tretinoin) in the same routine. Time-separated (peptide AM, retinoid PM) is the standard approach.
Peptide-vitamin C stacking: Using a peptide serum (especially copper peptide) and L-ascorbic acid vitamin C in the same step. Generally avoided: low-pH vitamin C destabilises copper peptide.
Glycine: The smallest amino acid. Roughly one-third of every collagen molecule. The amino acid the body needs more of than diet typically provides.
Proline: Cyclic amino acid. Roughly 15 percent of collagen. Provides structural rigidity to the triple helix.
Hydroxyproline: Modified proline. Vitamin C-dependent. The marker amino acid used to quantify collagen in tissue and blood.
Lysine: Essential amino acid. Combines with proline to form the crosslinks in mature collagen fibres.
Crowley 2009: RCT in osteoarthritis patients showing UC-II 40 mg/day outperformed glucosamine + chondroitin on joint function over 90 days.
Lugo 2016: RCT in active adults with knee pain showing UC-II 40 mg/day improved knee comfort during exercise.
Cult Beauty: UK premium beauty retailer. Major UK distribution channel for collagen and cosmetic peptide brands.
LookFantastic: UK beauty retailer. Major UK distribution for global collagen brands including Vital Proteins.
Holland and Barrett: UK high-street health retailer. Mid-tier collagen and supplement distribution.
Beauty Pie: UK members-only beauty subscription. Houses own-brand peptide products at member-only pricing.
GHRP: Growth Hormone Releasing Peptide. Class of synthetic peptides (Ipamorelin, GHRP-2, GHRP-6, hexarelin) that act at the ghrelin receptor.
GHRH: Growth Hormone Releasing Hormone. Endogenous hypothalamic 44-amino-acid hormone. Synthetic analogues include Sermorelin, Tesamorelin, CJC-1295.
GHSR-1a: Growth Hormone Secretagogue Receptor type 1a. The ghrelin receptor at which GHRPs (Ipamorelin, hexarelin) act.
DAC linker: Drug Affinity Complex linker. The chemical group attached to CJC-1295 that binds albumin and extends half-life from 30 minutes to 8+ days.
EGRIFTA: US brand name for tesamorelin. FDA-approved for HIV-associated lipodystrophy. The only UK-relevant peptide on this list with any major-market marketing authorisation.
Sikiric group: Research group at the University of Zagreb led by Predrag Sikiric. Origin of most BPC-157 preclinical literature from 2003 onwards.
Thymosin beta-4: Naturally occurring 43-amino-acid peptide present in most mammalian cells. TB-500 is a synthetic fragment.
Mitochondrial-derived peptide: Short peptides encoded by mitochondrial DNA rather than nuclear DNA. MOTS-c is the best-studied. Class of putative metabolic regulators.
mTOR: Mammalian target of rapamycin. Cellular pathway central to growth and longevity research. Some peptides modulate it indirectly.
AMPK: AMP-activated protein kinase. Cellular energy sensor. Activated by MOTS-c and other metabolic peptides in preclinical models.
Lyophilised: Freeze-dried. The standard delivery form for research peptides in glass vials. Stable at room temperature for short periods.
Bacteriostatic water: Sterile water with 0.9 percent benzyl alcohol added, a solvent referenced in research-peptide chemistry. Reconstituted solutions are far less stable than the lyophilised powder, and handling falls outside the scope of this editorial encyclopedia.
UKAD: UK Anti-Doping. The national anti-doping organisation. Enforces WADA prohibited list across UK competitive sport.
KPV: Lysine-Proline-Valine. Synthetic tripeptide corresponding to the C-terminal fragment of alpha-MSH. Preclinical IBD and wound-healing literature only. No human RCTs. Sold under "research use only" framing in the UK.
GHRP-2: Growth Hormone Releasing Peptide-2. Older synthetic hexapeptide ghrelin receptor agonist developed in the late 1980s. Human pharmacokinetic data only; no body-composition or anti-ageing RCTs. WADA prohibited. Research use only in the UK.
DSIP: Delta Sleep-Inducing Peptide. Synthetic nine-amino-acid peptide first isolated by Schoenenberger and Monnier in 1977. Older Russian and German EEG sleep-architecture literature only. Mechanism contested, no specific receptor identified. Research use only in the UK.
Cerebrolysin: Porcine brain-derived preparation containing a complex mixture of low-molecular-weight neuropeptides and free amino acids. Prescription-only medicine in Russia, Austria, Germany, Poland, and several other jurisdictions for stroke and dementia indications. No UK MHRA marketing authorisation. Larger Western RCTs and Cochrane reviews report mixed or modest effects with high heterogeneity. Research compound in the UK context.
Hexarelin: Synthetic hexapeptide growth hormone releasing peptide (GHRP), developed in the early 1990s. Ghrelin receptor (GHSR-1a) agonist with distinctive additional binding at the CD36 cardiovascular receptor in cardiac tissue. No body-composition RCTs published. WADA prohibited. Research use only in the UK.
GHRP-6: Growth Hormone Releasing Peptide-6. One of the earliest synthetic GHRPs, developed in the late 1980s. Ghrelin receptor agonist distinguished within the GHRP family by pronounced appetite stimulation via the ghrelin pathway. No body-composition RCTs published. WADA prohibited. Research use only in the UK.
GMC: General Medical Council. UK regulator of doctors. Every prescriber at a UK GLP-1 clinic holds a GMC registration.
CQC: Care Quality Commission. Regulator of UK health and social care services. Most UK longevity clinics are CQC-registered for the clinical interpretation component.
FSA: Food Standards Agency. Regulator of UK food supplements (including collagen and vitamins). Distinct from MHRA.
EAMS: Early Access to Medicines Scheme. MHRA route for unlicensed medicines to reach UK patients pre-approval. Not used for any current GLP-1.
Named-patient supply: UK route for prescribing an unlicensed medicine to a specific named patient. Outside the scope of routine GLP-1 supply.
Unlicensed medicinal product: A medicine without UK MHRA marketing authorisation. Includes any GLP-1 imported from outside the UK supply chain. MHRA enforcement target.
Specials: UK term for unlicensed medicines manufactured specifically for a UK patient by a registered specials manufacturer. Distinct from imported unlicensed.
Off-label: Use of a licensed medicine outside its UK MHRA indication. Legal when prescriber-initiated and clinically justified. Common for some GLP-1 uses.

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