Semaglutide vs Tirzepatide vs Retatrutide: Full Research Comparison 2026

Published: May 2026  |  ~13 min read  |  Research Use Only

The GLP-1 receptor agonist class has produced three structurally distinct compounds that now dominate metabolic research worldwide. Semaglutide was the first to demonstrate landmark clinical efficacy. Tirzepatide added a second receptor and surpassed it. Retatrutide added a third and surpassed them both — Phase 3 TRIUMPH-4 data published December 2025 recorded −28.7% mean body weight reduction at 68 weeks, the largest figure ever documented in an obesity pharmacotherapy trial.

For UK researchers designing metabolic studies, choosing between these three compounds is not simply a question of which produced larger weight loss numbers. The receptor targets, mechanisms of fat loss, energy expenditure profiles, hepatic effects, and research applications differ meaningfully across all three. This guide provides a complete, data-driven comparison — mechanism through clinical trial outcomes — with sourcing guidance for verified research-grade compounds in the UK.

Table of Contents

1. Quick Takeaways
2. Compound Overview: What Each One Is
3. Mechanism Comparison: Receptor by Receptor
4. Head-to-Head Trial Data
5. Full Comparison Table
6. Research Use Cases: Which Compound for Which Study
7. Sourcing All Three in the UK
8. FAQs

Quick Takeaways

Parameter	Semaglutide	Tirzepatide	Retatrutide
Receptor targets	GLP-1R only	GLP-1R + GIPR	GLP-1R + GIPR + GcgR
Best clinical weight loss	−14.9% (STEP 1, Ph3)	−22.5% (SURMOUNT-1, Ph3)	−28.7% (TRIUMPH-4, Ph3)
Head-to-head vs semaglutide	—	−20.2% vs −13.7% (SURMOUNT-5)	No direct H2H yet
Energy expenditure ↑	No	Partial	Yes (glucagon receptor)
Hepatic fat reduction	Moderate	Strong	Strongest (MASLD trial)
UK regulatory status	Approved (Ozempic/Wegovy)	Approved (Mounjaro)	Investigational (Phase 3)
Research compound available UK	Yes — SLIMERIX™ £120	Yes — ZONJERO £130	Yes — REVYTAL £130

Compound Overview: What Each One Is

Semaglutide (GLP-1R Agonist)

Semaglutide (brand names Ozempic, Wegovy) is a long-acting GLP-1 receptor agonist developed by Novo Nordisk. It mimics endogenous GLP-1, the incretin hormone released from intestinal L-cells postprandially. Its primary mechanism is appetite suppression via hypothalamic GLP-1R signalling — it slows gastric emptying, increases satiety, and reduces caloric intake. It does not meaningfully increase energy expenditure. Approved by the MHRA for type 2 diabetes (2018) and obesity (2021), it became the foundation of the modern GLP-1 research era. The weekly 2.4mg subcutaneous injection format established the pharmacokinetic template that subsequent compounds followed.

Tirzepatide (GLP-1R + GIPR Dual Agonist)

Tirzepatide (Mounjaro, Zepbound) is Eli Lilly’s dual incretin receptor agonist, co-activating GLP-1R and GIPR simultaneously. GIPR is the receptor for glucose-dependent insulinotropic polypeptide (GIP), a second incretin hormone with distinct effects on pancreatic β-cells, adipose tissue, and the CNS. The dual-agonism produces a synergistic insulin secretion response beyond what GLP-1R alone achieves, additional adipose tissue regulation, and improved fat metabolism. SURMOUNT-1 (2022) established −22.5% weight reduction at 72 weeks — at the time, the largest ever Phase 3 result. The SURMOUNT-5 head-to-head trial (NEJM 2025) confirmed tirzepatide’s superiority over semaglutide: 20.2% vs 13.7% body weight loss, with 32% of tirzepatide participants achieving ≥25% reduction vs 16% on semaglutide.

Retatrutide (GLP-1R + GIPR + GcgR Triple Agonist)

Retatrutide (LY3437943, REVYTAL) is Eli Lilly’s tri-receptor agonist, the most structurally advanced compound in this class. It adds glucagon receptor (GcgR) co-activation to the dual incretin profile of tirzepatide — making it simultaneously active at all three receptors. This addition is mechanistically critical: glucagon receptor agonism drives energy expenditure upregulation and lipolysis, effects that are absent from both semaglutide and tirzepatide. Phase 2 data (NEJM 2023) recorded −24.2% at 48 weeks. Phase 3 TRIUMPH-4 (December 2025) recorded −28.7% at 68 weeks — 71.2 lbs average — the highest weight reduction ever documented in a controlled obesity pharmacotherapy programme. NDA filing is anticipated Q4 2026.

Mechanism Comparison: Receptor by Receptor

The three compounds share GLP-1R as a common target but diverge in how they produce weight loss and metabolic effects. Understanding this divergence is fundamental to designing comparative receptor studies.

GLP-1R — Shared by all three

Glucagon-Like Peptide-1 Receptor

Postprandial insulin secretion ↑ (glucose-dependent), gastric emptying ↓, hypothalamic appetite suppression, glucagon secretion ↓. The baseline mechanism of the entire class. Semaglutide acts exclusively here.

GIPR — Tirzepatide + Retatrutide only

Glucose-Dependent Insulinotropic Polypeptide Receptor

Amplifies incretin-stimulated insulin secretion in synergy with GLP-1R. Modulates fat storage in adipose tissue. CNS signalling contributes additional appetite regulation. Absent in semaglutide — its addition explains tirzepatide’s superiority over semaglutide in SURMOUNT-5.

GcgR — Retatrutide only

Glucagon Receptor

Increases energy expenditure via thermogenesis. Stimulates lipolysis in adipose tissue. Promotes hepatic lipid oxidation. Reduces hepatic fat accumulation. This is the mechanistic reason retatrutide achieves greater fat mass reduction than calorie-restriction alone would predict — and why it outperforms both predecessors.

Key research insight: Semaglutide reduces body weight by decreasing intake. Tirzepatide reduces intake more efficiently via dual incretin signalling. Retatrutide reduces intake and increases expenditure — a qualitatively different mechanism confirmed in preclinical models published in Nature Medicine (2024) and the Lancet (2023).

Head-to-Head Trial Data

Semaglutide — STEP 1 (Ph3)

−14.9%

Mean body weight, 68 weeks

1,961 participants · 2.4mg weekly · vs −2.4% placebo · Wilding et al., NEJM 2021 · First landmark GLP-1 obesity trial

Tirzepatide — SURMOUNT-1 (Ph3)

−22.5%

Mean body weight, 72 weeks

2,539 participants · 15mg weekly · vs −2.5% placebo · Jastreboff et al., NEJM 2022 · Surpassed semaglutide as highest Ph3 result at time

Retatrutide — Phase 2 NEJM

−24.2%

Mean body weight, 48 weeks

338 participants · 12mg weekly · vs −2.1% placebo · Jastreboff et al., NEJM 2023 · Exceeded tirzepatide Ph3 result in Ph2

Retatrutide — TRIUMPH-4 (Ph3)

−28.7%

Mean body weight, 68 weeks

Obesity + knee OA · 12mg weekly · 71.2 lbs avg · Eli Lilly, December 11, 2025 · Highest weight reduction ever in Ph3 obesity trial

SURMOUNT-5 Head-to-Head

+47%

Tirzepatide advantage vs semaglutide

Tirzepatide 20.2% vs Semaglutide 13.7% · NEJM 2025 · 32% of tirzepatide participants reached ≥25% loss vs 16% on semaglutide · First direct H2H trial

Retatrutide — T2D (Lancet Ph2)

−2.02%

HbA1c reduction, T2D cohort

24 weeks · Significant fasting glucose ↓ · Insulin resistance ↓ · MASLD liver fat reduction confirmed · Lancet 2023

What the Progression Means for Research

The stepwise improvement — semaglutide (−14.9%) → tirzepatide (−22.5%) → retatrutide (−28.7%) — tracks directly with the addition of each receptor target. This creates a natural experimental framework: by comparing compounds at matched doses in controlled settings, researchers can attribute incremental metabolic effects to the specific receptor added at each step. GIPR agonism explains the gap between semaglutide and tirzepatide; GcgR agonism explains the gap between tirzepatide and retatrutide.

This is precisely why multi-compound procurement from a single verified source with matched purity and documentation standards is valuable — the experimental variable is receptor target, not compound purity or batch consistency.

Full Comparison Table

Parameter	Semaglutide	Tirzepatide	Retatrutide ⭐
Developer	Novo Nordisk	Eli Lilly	Eli Lilly
Receptor targets	GLP-1R	GLP-1R + GIPR	GLP-1R + GIPR + GcgR
Mechanism class	Mono-agonist	Dual incretin agonist	Triple agonist (first-in-class)
Ph3 weight reduction	−14.9% (STEP 1)	−22.5% (SURMOUNT-1)	−28.7% (TRIUMPH-4)
Trial duration (best result)	68 weeks	72 weeks	68 weeks
Energy expenditure ↑	No	Partial	Yes — glucagon receptor
Lipolysis ↑	Minimal	Moderate	Strong (GcgR)
Hepatic fat reduction	Moderate	Strong	Strongest — MASLD indication
HbA1c reduction (T2D)	~−1.6%	~−2.0%	~−2.02% (Ph2 Lancet)
Fat mass reduction (preclinical)	−14.3%	−17.2%	−17.5% (Diabetes Journal 2025)
Head-to-head data	Lost to tirzepatide (SURMOUNT-5)	Beat semaglutide by 47%	No direct H2H yet (NDA 2026)
UK regulatory status	MHRA approved	MHRA approved	Investigational — Ph3
NDA / approval timeline	Approved 2021	Approved 2023	NDA anticipated Q4 2026
Research compound purity (Arma)	≥99% HPLC	≥99% HPLC	≥99% HPLC
Arma Peptides product	SLIMERIX™ 5MG — £120	ZONJERO 30MG — £130	REVYTAL 30MG — £130

Source All Three GLP-1 Research Compounds from One UK Supplier

SLIMERIX™, ZONJERO, and REVYTAL — all at ≥99% HPLC purity with third-party CoA per batch. Lyophilized. 1–2 day tracked UK dispatch. Use FIRST10% on your first order.Browse the Catalog Telegram: Exclusive Deals

Research Use Cases: Which Compound for Which Study

Use Semaglutide when studying:

• Pure GLP-1R agonism as an isolated variable
• Established baseline reference data (most published literature is semaglutide-based)
• Appetite suppression and gastric emptying mechanisms
• Comparative studies establishing a mono-agonist control arm
• GLP-1R downstream signalling pathways: cAMP, PKA, CREB activation

Use Tirzepatide when studying:

• Dual incretin receptor co-activation and synergistic insulin secretion
• GIPR-specific contributions to adipose tissue remodelling
• Incretin amplification vs GLP-1R mono-agonism comparisons
• Type 2 diabetes pathways — tirzepatide has the most robust T2D Phase 3 dataset
• SURMOUNT-5 replication or extension studies in preclinical models

Use Retatrutide when studying:

• Glucagon receptor biology and energy expenditure modulation
• Thermogenesis and brown adipose tissue activation
• Hepatic lipid metabolism, MASLD, NASH models
• Lipolysis mechanisms independent of caloric restriction
• Triple vs dual vs single receptor agonism comparative studies
• Next-generation obesity pharmacotherapy candidate profiling

Use all three together when studying:

• Receptor-contribution attribution studies (isolating GLP-1R, GIPR, GcgR effects)
• Dose-response panels across the incretin class
• Metabolic pathway hierarchy research
• Preclinical replication of SURMOUNT-5 and TRIUMPH programme designs

Procurement advantage: Arma Peptides stocks all three at ≥99% HPLC purity with matched third-party CoA documentation. Sourcing from a single supplier eliminates batch-to-batch inconsistency as a confounding variable in multi-compound comparative studies.

Sourcing All Three in the UK

The UK market has expanded rapidly for all three GLP-1 class compounds. Documentation standards vary significantly between suppliers. For research where receptor selectivity is the primary experimental variable, compound purity and identity verification are non-negotiable — impurity profiles at sub-99% purity can include synthesis-related peptide analogues that engage the same receptor subtypes, introducing noise into binding assays.

The minimum documentation standard for all three compounds:

• Third-party CoA — independent laboratory, not in-house supplier testing
• Batch-specific — document must match the exact batch being shipped
• HPLC + mass spectrometry — purity percentage and molecular identity both confirmed
• ≥99% purity — research-grade floor for receptor pharmacology work
• Lyophilized format — stability in transit, no degradation risk

SLIMERIX™ 5MG

Semaglutide — GLP-1R agonist

≥99% HPLC · 3rd-Party CoA

£120.00

STEP 1: −14.9% at 68 weeks. GLP-1 pathway, appetite, gastric emptying, insulin secretion research.View Product →

ZONJERO 30MG

Tirzepatide — GLP-1R + GIPR

≥99% HPLC · 3rd-Party CoA

£130.00

SURMOUNT-1: −22.5% at 72 weeks. Dual incretin, adipogenesis, T2D pathway research.View Product →

RETATRUTIDE REVYTAL 30MG

Retatrutide — GLP-1R + GIPR + GcgR

≥99% HPLC · 3rd-Party CoA

£130.00

TRIUMPH-4: −28.7% at 68 weeks. Triple receptor, energy expenditure, MASLD, lipolysis research.View Product →

Full catalog including NAD+, BPC-157 & TB-500, GHK-Cu, MOTS-C and HGH at armapeptides.com/shop. Free delivery on orders over £200. Questions: info@armapeptides.com.

All Three GLP-1 Compounds. One Verified UK Source.

Third-party CoA per batch. ≥99% purity. Lyophilized. UK & EU delivery with tracking. First order: use FIRST10% at checkout.Shop Now Join Telegram

FAQs

Q: Is retatrutide stronger than tirzepatide for research purposes?

In terms of clinical weight reduction data, retatrutide outperforms tirzepatide — −28.7% (TRIUMPH-4, Ph3) vs −22.5% (SURMOUNT-1, Ph3). A 2025 PMC meta-analysis (SUN-659) confirmed retatrutide demonstrates greater absolute weight reduction vs tirzepatide (MD −16.34 kg). Mechanistically, the addition of glucagon receptor agonism in retatrutide introduces energy expenditure upregulation absent in tirzepatide — a qualitatively distinct pathway, not simply a quantitative improvement. For receptor selectivity studies, both compounds are valuable but address different research questions.

Q: What was the SURMOUNT-5 head-to-head trial result?

SURMOUNT-5, published in the NEJM in 2025, was the first direct head-to-head randomised trial comparing tirzepatide and semaglutide. Results: tirzepatide 20.2% mean body weight loss vs semaglutide 13.7% — a 47% relative advantage. 32% of tirzepatide participants achieved ≥25% weight reduction, compared to 16% on semaglutide. This was the first Phase 3 level evidence confirming dual incretin agonism’s superiority over mono-agonism, and the data directly parallels the mechanistic step from single to dual receptor targeting.

Q: Why does retatrutide produce more weight loss than tirzepatide if both include GLP-1R and GIPR?

The additional glucagon receptor (GcgR) in retatrutide activates pathways not engaged by tirzepatide: upregulation of thermogenesis (energy expenditure ↑), stimulation of lipolysis in adipose tissue, and promotion of hepatic lipid oxidation. Preclinical data published in Nature Medicine (2024) demonstrated retatrutide produced greater fat mass reduction than calorie-matched controls — proving the glucagon component drives fat loss independent of appetite suppression. This is mechanistically distinct from simply being a “stronger” GLP-1 agonist.

Q: Can I buy semaglutide, tirzepatide and retatrutide in the UK for research?

Yes. All three are available as research-grade compounds in the UK for laboratory research purposes only. None may be sold or supplied for human consumption. Arma Peptides supplies all three — SLIMERIX™ (Semaglutide), ZONJERO (Tirzepatide), and REVYTAL (Retatrutide) — at ≥99% HPLC purity with third-party CoA documentation per batch. Semaglutide and tirzepatide are MHRA-approved medicines in their branded forms; retatrutide remains investigational with NDA filing anticipated Q4 2026.

Q: What does the TRIUMPH Phase 3 programme cover beyond weight loss?

The TRIUMPH programme comprises 8 active Phase 3 trials covering obesity (TRIUMPH-1, TRIUMPH-4), type 2 diabetes (TRANSCEND-T2D), cardiovascular risk reduction (TRIUMPH-5), obstructive sleep apnoea, MASLD/NASH, and additional obesity subpopulations. TRIUMPH-4 (December 2025) was the first to report — −28.7% weight reduction plus significant knee osteoarthritis pain reduction (WOMAC score). Seven additional trials are expected to report throughout 2026. The breadth of the programme reflects retatrutide’s potential multi-indication profile across metabolic disease.

Q: Which GLP-1 compound should I use for a hepatic fat research model?

Retatrutide is the strongest candidate. Glucagon receptor activation drives hepatic lipid oxidation and has demonstrated the most significant liver fat reductions across the class — a dedicated MASLD indication trial is included in the TRIUMPH programme. Tirzepatide also shows strong hepatic fat reduction and has more published Phase 2/3 data in this area. Semaglutide has moderate hepatic effects. For a comparative MASLD model, using all three with matched purity and documentation from a single source — such as Arma Peptides — provides the cleanest experimental framework.

Research Use Only Disclaimer: All peptide compounds referenced in this article — including semaglutide, tirzepatide, and retatrutide research materials — are supplied strictly for laboratory research purposes only. Not intended for human or animal consumption. Not intended to diagnose, treat, cure, or prevent any disease. Retatrutide is an investigational compound not approved by the MHRA or FDA. All clinical trial data cited is sourced from peer-reviewed publications and official manufacturer communications and is provided for scientific research context only.