The leading peptides researched for weight loss in the UK in 2026 are semaglutide, tirzepatide, retatrutide, CagriSema, AOD-9604, MOTS-c, and somatropin. Each operates through a distinct mechanism, from GLP-1 (glucagon-like peptide-1) receptor agonism to amylin analogue signalling. This guide explains how each compound works, what the research shows, and how to select the right one for your protocol.
You will learn:
- How GLP-1 agonists, dual agonists, and triple agonists differ mechanistically and in research outcomes
- Which peptides suit short-term versus extended research timelines
- Current UK pricing, formats, and availability for each compound
CagriSema delivered a mean body-weight reduction of 22.7% over 68 weeks in the REDEFINE-1 phase 3 programme (topline results announced 20 December 2024), compared with 16.1% for semaglutide 2.4 mg alone and 12.0% for cagrilintide alone. That gap shows how combination peptide research has moved beyond single-agonist approaches.
The peptides covered in this guide, ranked by current research depth:
- Semaglutide, GLP-1 receptor agonist; the most extensively trialled compound in this category
- Tirzepatide, dual GIP (glucose-dependent insulinotropic polypeptide)/GLP-1 agonist; a 2026 UK cost-to-target analysis found lower annual pharmacy cost per patient than subcutaneous semaglutide 1 mg in type 2 diabetes care
- CagriSema, fixed combination of cagrilintide 2.4 mg + semaglutide 2.4 mg; phase 3 data published 2024
- Cagrilintide, long-acting amylin analogue; standalone arm in REDEFINE-1 produced 12.0% mean weight reduction
- Retatrutide, triple GLP-1/GIP/glucagon agonist; phase 2 data available, phase 3 ongoing
- AOD-9604, growth hormone fragment 176–191; research-grade compound
- MOTS-c, mitochondrial-derived peptide; early-stage research
- Somatropin, recombinant human growth hormone; available in licensed and research formats in the UK
GLP-1 Receptor Agonists: Semaglutide & Tirzepatide
Semaglutide and tirzepatide are the two most extensively researched GLP-1-based peptides for weight loss currently available in the UK. Semaglutide acts on a single receptor; tirzepatide targets two.
Key differences:
- Semaglutide, selective GLP-1 receptor agonist; slows gastric emptying, suppresses appetite via hypothalamic signalling, and modulates postprandial glucose
- Tirzepatide, dual GIP/GLP-1 agonist; adds GIP receptor activation, which appears to amplify fat-cell lipolysis beyond GLP-1 agonism alone
- Research format (semaglutide), available as a 6-week prefilled pen, suited to shorter observation windows
- Research format (tirzepatide), available in 30-dose and 60-dose pen configurations, covering both short-term and extended research timelines
A 2026 peer-reviewed cost-to-target analysis found tirzepatide at 5 mg, 10 mg, and 15 mg carried a lower annual pharmacy cost per patient reaching composite treatment endpoints than subcutaneous semaglutide 1 mg in UK type 2 diabetes care.
How GLP-1 Agonism Works
GLP-1 is an incretin hormone released from intestinal L-cells in response to food intake. Synthetic GLP-1 receptor agonists mimic this signal with a longer half-life than the endogenous peptide. The result is slowed gastric emptying, reduced caloric intake driven by central appetite suppression, and improved postprandial insulin secretion. Semaglutide shares approximately 94% amino acid homology with native GLP-1 and is modified to resist dipeptidyl peptidase-4 degradation.
Semaglutide vs. Tirzepatide: What the Research Shows
Semaglutide's weight-loss profile is well-characterised across the STEP trial programme, which established it as the reference compound in this category. Tirzepatide's SURMOUNT programme subsequently reported larger mean weight reductions at the highest doses, consistent with the additive effect of dual receptor engagement. The 2026 UK cost analysis puts tirzepatide in a cost-competitive position for structured research settings.
For researchers sourcing these compounds in the UK, the HD Semaglutide 10 Pen offers a ready-to-use format without reconstitution. Those comparing formats across the dual-agonist category can review available configurations on the Tirzepatide hub page. Both are supplied as research-grade compounds and are not presented here as prescription medications or licensed treatments.
Retatrutide: The Next-Generation Triple Agonist
Retatrutide targets GLP-1, GIP, and glucagon receptors simultaneously, making it the most mechanistically complex compound in this category as of 2026. Where tirzepatide engages two receptors, retatrutide adds glucagon receptor agonism to the combination.
Why Glucagon Agonism Matters
The glucagon component is what separates retatrutide from dual agonists. Glucagon receptor activation drives hepatic glucose output and, at the doses used in research settings, increases fatty acid oxidation and thermogenesis. The hypothesis is that glucagon agonism mobilises stored fat more directly than GLP-1 or GIP signalling alone, both of which operate primarily through appetite suppression and insulin secretion. This additive mechanism explains why retatrutide has attracted significant research interest, though the evidence base remains thinner than for semaglutide or tirzepatide given its later stage of development.
Phase 3 Status and Research Timelines
Retatrutide entered phase 3 trials in 2024–2025, with registration studies listed on ClinicalTrials.gov. Phase 2 data published in 2023 reported substantial mean weight reductions at the highest doses over 48 weeks, but phase 3 primary endpoints had not been reported at the time of writing. Treat retatrutide as a compound with a promising but still-maturing evidence base compared with the completed STEP and SURMOUNT programmes behind semaglutide and tirzepatide.
Because phase 3 timelines are extended, retatrutide suits longer research protocols. The 32-dose pen (8 mg total) works for 6–8 week studies, while the 64-dose pen (16 mg total) supports 12-week-plus protocols where sustained receptor engagement is the research objective. Both formats are available in the UK as research-grade compounds.
Researchers already familiar with the dual-agonist category can review the Tirzepatide hub page for format comparisons before deciding whether the additional glucagon axis justifies moving to a triple agonist. Those using GLP-1 single agonists as a baseline reference may find the HD Semaglutide 10 Pen useful for establishing a comparator within the same research programme.
Triple agonism is newer and less widely studied than GLP-1 agonism alone. The glucagon receptor component introduces a distinct metabolic pathway, but that also means the long-term tolerability profile is less characterised than for compounds with decade-long clinical datasets.
Mitochondrial & Metabolic Peptides: MOTS-c and AOD-9604
Not every weight-loss peptide works through appetite suppression. MOTS-c and AOD-9604 operate via distinct metabolic pathways, which makes them relevant to researchers who want mechanistic diversity rather than a second GLP-1 agonist.
MOTS-c: Mitochondrial-Derived Metabolic Signalling
MOTS-c is a 16-amino-acid mitochondrial-derived peptide encoded within the mitochondrial genome and the only known mitochondria-derived peptide with documented effects on cellular energy metabolism. Rather than reducing caloric intake, MOTS-c activates AMPK (adenosine monophosphate-activated protein kinase) signalling and improves mitochondrial substrate utilisation, a mechanism studied in the context of exercise physiology and metabolic flexibility. Research published in Cell Metabolism and Molecular Metabolism between 2023 and 2024 characterised its role in skeletal muscle glucose uptake and fatty acid oxidation under energy-deficit conditions. The UK research format is a 32-dose pen, suited to protocols examining metabolic adaptation over 6–8 weeks.
AOD-9604: HGH Fragment Targeting Lipolysis
AOD-9604 is a synthetic HGH (human growth hormone) fragment corresponding to amino acids 176–191 of the human growth hormone sequence. It retains the lipolytic signalling properties of the parent molecule without activating the IGF-1 (insulin-like growth factor 1) axis or producing systemic growth-hormone effects, which is the primary reason it attracts interest as a research compound distinct from full-sequence somatropin. Mechanistic studies from 2023 confirmed its interaction with beta-adrenergic receptors in adipose tissue, stimulating lipolysis signalling without the proliferative downstream effects associated with intact hGH. The UK format is a 2 mg vial, typically used in short-duration lipolysis-focused protocols.
Positioning Within a Research Programme
Both compounds are complementary to GLP-1 agonists rather than substitutes. A researcher using the HD Semaglutide 10 Pen as a primary intervention could incorporate MOTS-c to examine whether mitochondrial pathway activation produces additive metabolic effects, or use AOD-9604 to isolate lipolysis signalling as a separate variable. Researchers already working with dual agonists can review the Tirzepatide hub page to assess whether adding a mitochondrial or lipolytic compound introduces meaningful mechanistic contrast within the same protocol.
These compounds are less mainstream than the GLP-1 and GIP agonist categories, and the clinical evidence base is correspondingly earlier-stage. Their value in a research context lies precisely in that mechanistic separation from appetite-centred pathways.
Combination Peptides: CagriSema & Thermogenic Stacks
CagriSema is a fixed-dose combination of cagrilintide 2.4 mg (a long-acting amylin analogue) and semaglutide 2.4 mg, delivering dual-mechanism action through amylin receptor agonism alongside GLP-1 receptor agonism within a single subcutaneous pen. REDEFINE-1 topline data published 20 December 2024 reported a mean body-weight reduction of 22.7% at 68 weeks for CagriSema 2.4/2.4 mg, compared with 16.1% for semaglutide 2.4 mg alone and 3.3% for placebo. The gap between the combination and the single agent reflects the additive contribution of amylin-pathway satiety signalling on top of GLP-1-mediated appetite suppression.
CagriSema as a Research Format
The Body Pharm CagriSema pen consolidates both compounds into one device, removing the need to source and administer two separate injections. For researchers already familiar with the HD Semaglutide 10 Pen, the CagriSema format is a mechanistic step up rather than a category change. An open-label phase 3 comparison cited in 2026 reporting placed CagriSema at 23.0% weight loss versus 25.5% for tirzepatide, suggesting the two approaches are broadly comparable in magnitude, though direct head-to-head data should be interpreted cautiously given the open-label design. Researchers evaluating dual agonists can review the Tirzepatide hub page for context on the GLP-1/GIP mechanism as a comparator.
Thermogenic Stacks: A Separate Mechanism
Thermogenic combinations such as the BP CYT3 (clenbuterol 40 mcg, yohimbine 10 mg, T3) operate through entirely different pathways: beta-2 adrenergic stimulation, alpha-2 adrenergic blockade, and thyroid hormone elevation. These compounds target basal metabolic rate and thermogenesis rather than appetite or incretin signalling, making them mechanistically distinct from GLP-1 or amylin agonists. The clinical evidence base for thermogenic stacks in structured obesity research is considerably thinner than for CagriSema or tirzepatide, and the cardiovascular and thyroid-axis implications require careful consideration within any research protocol.
CagriSema is the exception among combination approaches, with phase 3 data now available; thermogenic stacks remain earlier-stage by comparison.
Growth Hormone & Recovery: Somatropin for Metabolic Support
Somatropin (recombinant human growth hormone) is a metabolic and recovery support agent, not a primary weight-loss compound. Its role in body-composition research centres on lean-mass retention and lipolysis rather than appetite suppression or incretin signalling, which puts it in a different category from the GLP-1 agonists discussed above.
What the Research Shows
Growth hormone stimulates lipolysis via hormone-sensitive lipase and promotes nitrogen retention, both of which support lean-mass preservation during caloric restriction. A 2023 analysis published in the Journal of Clinical Endocrinology & Metabolism found that GH replacement in GH-deficient adults reduced fat mass and improved lean body mass, though effects in non-deficient populations were more modest and dose-dependent. In structured research protocols, somatropin is frequently paired with GLP-1 agonists to offset the lean-mass losses that accompany aggressive caloric restriction, rather than being used as a standalone fat-loss agent.
UK Formats Available
Body Pharm somatropin is available through JCSG UK in three formats, each suited to different research requirements:
- 40 IU pen, a lower-dose prefilled option; no reconstitution required, suited to protocols where precise low-range dosing is the priority
- 100 IU pen, higher-dose prefilled format for longer research windows without the need for aseptic mixing
- 100 IU reconstitution kit, lyophilised format requiring sterile diluent; preferred where researchers need granular dose titration or are running extended multi-compound protocols
The reconstitution kit demands strict aseptic technique and refrigerated storage post-mixing, which adds procedural complexity compared with the pen formats. Researchers already sourcing GLP-1 compounds such as the HD Semaglutide 10 Pen or reviewing dual-agonist options via the Tirzepatide hub will find somatropin most relevant as a complementary agent within a broader protocol rather than a first-line selection.
Comparison Table: Peptides, Mechanisms & UK Formats
The seven peptides covered in this article span four distinct mechanistic categories: GLP-1 agonism, dual and triple receptor agonism, mitochondrial signalling, and growth hormone activity. The table below maps each one to its UK format, typical research dosing, and key differentiator.
Key facts at a glance:
- Semaglutide is a GLP-1 receptor agonist available via the HD Semaglutide 10 Pen with a well-established phase 3 evidence base
- Tirzepatide is a GLP-1/GIP dual agonist; full format options are listed on the Tirzepatide hub page
- CagriSema produced a 22.7% mean body-weight reduction at 68 weeks in REDEFINE-1 (topline data, 20 December 2024), versus 16.1% for semaglutide 2.4 mg alone
- Prices marked † are supplier-reported and subject to change; verify current figures on the relevant JCSG UK product page before ordering
Quick-Reference Table
| Peptide | Mechanism | UK Format(s) | Typical Research Dosing | Research Timeline | Approx. UK Price | Key Advantage |
|---|---|---|---|---|---|---|
| Semaglutide | GLP-1 receptor agonist | 6-week prefilled pen | 0.25–1 mg/week, titrated | 6+ weeks | See product page† | Largest phase 3 dataset in class |
| Tirzepatide | GLP-1 + GIP dual agonist | 30-dose and 60-dose pens | 2.5–15 mg/week, titrated | 6–12 weeks | See product page† | Dual-receptor mechanism; 2026 UK cost-to-target analysis favoured it over semaglutide 1 mg |
| Retatrutide | GLP-1 + GIP + glucagon triple agonist | 32-dose and 64-dose pens | 0.5–8 mg/week, titrated | 12+ weeks | See product page† | Only triple agonist in this comparison |
| MOTS-c | Mitochondrial-derived peptide; AMPK activation | 32-dose pen | 10 mg/day | 6–12 weeks | See product page† | Fat-metabolism pathway independent of appetite suppression |
| AOD-9604 | HGH fragment 176–191; lipolysis stimulation | 2 mg lyophilised vial | 0.3–0.5 mg/day | 8–12 weeks | See product page† | Targeted lipolytic action without full HGH receptor binding |
| CagriSema | Amylin analogue (cagrilintide) + GLP-1 agonist (semaglutide) fixed combination | Single prefilled pen | 0.5–2.4 mg/week per component, titrated | 6–12 weeks (phase 3 ran 68 weeks) | See product page† | REDEFINE-1 showed superior weight loss vs. either monotherapy at 68 weeks |
| Somatropin | Recombinant human growth hormone; IGF-1 axis activation | 40 IU pen, 100 IU pen, 100 IU reconstitution kit | 2–4 IU/day | 12+ weeks | See product page† | Lean-mass preservation; most relevant as a complement to GLP-1 protocols |
Notes on Reading This Table
Dosing figures reflect ranges reported in published research protocols, not prescriptive guidance. Research timelines indicate the minimum window typically used in structured studies; longer durations are common for HGH-axis compounds. Prices are not fixed in this table because UK supplier pricing changes; the JCSG UK product pages carry live figures. CagriSema's 68-week timeline reflects the REDEFINE-1 phase 3 programme; shorter exploratory windows have been used in earlier phase 2b work.
How to Choose the Right Peptide for Your Research Protocol
The right peptide for a weight-loss research protocol depends on four variables: the intended study duration, the mechanism you want to isolate, the format your workflow supports, and the cost per dose across that timeline. No single best option exists; the compounds in this list serve different research questions.
Research Timeline
Shorter protocols of six to eight weeks suit prefilled pen formats. An eight-week appetite-suppression study maps cleanly onto the HD Semaglutide 10 Pen, which provides a fixed dose count without reconstitution. A sixteen-week or longer protocol justifies the 64-dose Retatrutide pen, where the titration schedule requires enough doses to reach and sustain the target weekly amount. Lyophilised kits such as the AOD-9604 2 mg vial suit researchers who need precise sub-milligram dosing flexibility that prefilled pens do not offer.
Mechanism Preference
Appetite suppression via GLP-1 receptor agonism points toward semaglutide or, for dual GLP-1/GIP activity, tirzepatide. Researchers isolating fat-metabolism pathways without appetite effects should consider MOTS-c, which activates AMPK independently of the incretin axis. AOD-9604 targets lipolysis specifically, without engaging the full growth hormone receptor. Where lean-mass retention is a co-primary endpoint alongside weight reduction, somatropin is the most relevant addition, typically run alongside a GLP-1 agonist rather than as a standalone compound.
Format and Practical Workflow
Prefilled pens remove reconstitution steps and reduce handling variables, which matters in tightly controlled protocols. Reconstitution kits give greater dose granularity and are often more cost-efficient per milligram at higher quantities. CagriSema's single prefilled pen combines cagrilintide and semaglutide in a fixed ratio, which simplifies a dual-mechanism protocol but removes the ability to adjust each component independently.
Budget and Cost Per Dose
Cost per dose varies significantly across formats and suppliers. A 32-dose MOTS-c pen at a fixed daily dose of 10 mg covers roughly one month; a 64-dose Retatrutide pen at a titrated weekly schedule spans three to four months. Calculate cost per week of active dosing, rather than cost per unit, to compare budgets accurately across compounds with different dose frequencies. JCSG UK product pages carry current pricing for each format.
Combination Approaches
REDEFINE-1 topline data reported a 22.7% mean body-weight reduction for CagriSema 2.4/2.4 mg at 68 weeks, versus 16.1% for semaglutide monotherapy and 12.0% for cagrilintide monotherapy. That gap is why combination protocols are increasingly the reference point in obesity research. A somatropin-plus-GLP-1 stack addresses a different question: preserving lean mass during a caloric-deficit protocol, rather than maximising total weight reduction.
UK Availability, Pricing & Ordering
JCSG stocks all compounds covered in this article and ships from the UK, with current pricing listed directly on each product page. Because prices shift with batch availability and format, the figures below reflect approximate ranges rather than fixed retail prices. Check the live pages before ordering.
GLP-1 and Dual Agonists
The HD Semaglutide 10 Pen is available as a prefilled 6-week pen; pricing sits in the £180–£220 range depending on current stock. Tirzepatide is offered in two pen formats: a 30-dose pen (approximately £190–£240) and a 60-dose pen (approximately £320–£380), with the higher-count format offering a lower cost per dose for longer protocols.
Triple Agonists and Mitochondrial Peptides
Retatrutide is available in 32-dose and 64-dose prefilled pens, priced at approximately £220–£270 and £380–£440 respectively. MOTS-c 32-dose pens sit in the £160–£200 range. AOD-9604 2 mg kits are typically the most accessible entry point in this category, priced at approximately £60–£90 per unit.
HGH Formats
Somatropin is available across three formats with meaningfully different price points:
- 40 IU prefilled pen: approximately £120–£160
- 100 IU prefilled pen: approximately £240–£290
- 100 IU reconstitution kit: approximately £200–£260
The kit format generally offers a lower per-IU cost at higher quantities, though it requires sterile diluent and aseptic handling. Prefilled pens remove that variable for researchers prioritising consistency over cost efficiency.
Lead Times and Storage
JCSG dispatches UK orders typically within one to three working days, though lead times are supplier-reported and subject to stock levels. Confirm at point of order. All peptide formats require refrigerated storage between 2°C and 8°C; reconstitution kits should be used promptly once prepared. Prices shown above are indicative as of mid-2026; visit JCSG product pages for real-time availability and current pricing.
Safety, Storage & Research Considerations
Every peptide listed in this article is a research-grade compound and should be handled according to laboratory protocols, not treated as a consumer supplement or self-administered therapeutic.
Storage Requirements
Most peptides in this category require refrigerated storage between 2°C and 8°C. This applies to prefilled pen formats including the HD Semaglutide 10 Pen and Tirzepatide pens, as well as lyophilised reconstitution kits. Peptides stored outside this range risk degradation that may not be visually apparent.
Reconstitution and Aseptic Technique
Reconstitution kits, such as the somatropin 100 IU format, require sterile bacteriostatic water and strict aseptic technique throughout preparation. Contamination at the mixing stage compromises the integrity of the compound entirely. Researchers should work in a clean environment, use fresh needles and syringes for each preparation, and discard any reconstituted solution that appears cloudy or particulate.
Following Published Protocols
Draw dosing and administration guidance for these compounds from published clinical trial protocols. The STEP, SURMOUNT, and RECOMP-GLP programmes provide the most detailed administration frameworks currently available for GLP-1 and dual-agonist peptides. CagriSema's REDEFINE-1 phase 3 programme ran over 68 weeks, which illustrates that meaningful research timelines extend well beyond short-term observation periods.
For mechanistic context on how these compounds interact at the receptor level, JCSG's resources on protein-peptide interactions and cellular function provide useful foundational reading before beginning any research protocol. Browse the full range of research-grade peptides available for UK delivery on the JCSG peptides hub.
Key Takeaways
- GLP-1 agonists (semaglutide, tirzepatide) remain the most extensively researched category; tirzepatide's dual-receptor mechanism produces larger mean weight reductions and lower cost per dose in 2026 UK analyses
- Triple agonists (retatrutide) add glucagon-driven thermogenesis and lipolysis but carry a thinner evidence base; suited to longer protocols where phase 3 data maturation is acceptable
- Combination peptides (CagriSema) show superior outcomes to monotherapy; REDEFINE-1 reported 22.7% weight loss versus 16.1% for semaglutide alone
- Metabolic peptides (MOTS-c, AOD-9604) operate independently of appetite suppression and suit researchers seeking mechanistic diversity
- Somatropin is most valuable as a lean-mass-preservation adjunct to GLP-1 protocols rather than a standalone weight-loss agent
- Format selection depends on study duration, dose granularity needs, and cost per dose; prefilled pens suit shorter protocols, reconstitution kits offer cost efficiency at scale
- UK pricing ranges from £60–£90 (AOD-9604) to £380–£440 (64-dose Retatrutide); verify current figures on JCSG product pages before ordering
Next Steps
Review the JCSG peptides hub to compare current UK pricing and availability across all formats. If your protocol prioritises appetite suppression with the largest evidence base, start with the HD Semaglutide 10 Pen. For dual-receptor engagement or cost-per-dose efficiency, explore the Tirzepatide hub page. If your research timeline exceeds 12 weeks and you want to evaluate triple agonism, contact JCSG directly to discuss Retatrutide pen configurations and phase 3 protocol alignment. For mechanistic contrast or lean-mass preservation, cross-reference MOTS-c, AOD-9604, or somatropin formats against your primary compound to ensure complementary rather than redundant pathways.