GLP-1, GIP and Glucagon Receptor Agonists — Semaglutide vs Tirzepatide vs Retatrutide (Ireland 2026)

By the Peptides Lab Ireland research team · Updated July 2026

Modern metabolic research peptides fall into three generations distinguished by receptor engagement: GLP-1 mono-agonists, GLP-1/GIP dual agonists, and GLP-1/GIP/glucagon triple agonists. This guide compares the three lead compounds Irish research groups order most heavily , Semaglutide, Tirzepatide and Retatrutide — and explains the receptor pharmacology behind each.

Receptor engagement overview

Semaglutide . The GLP-1 reference compound

Semaglutide is a synthetic 31-amino acid analogue of native GLP-1 (7-37) with fatty-acid modification (γ-glutamyl-C18 di-acid) at Lys26 for albumin binding and extended half-life. It selectively activates the GLP-1 receptor.

Research focus areas:

• GLP-1 receptor pharmacology in vitro (β-cell insulin secretion, glucagon suppression)
• Central appetite regulation research (hypothalamic circuit studies)
• Gastrointestinal motility and emptying models
• Cardiovascular research (endothelial function, atherosclerosis models)
• Neuroprotection research (dopaminergic, neurodegeneration models)

See our Semaglutide Ireland research reference. Semaglutide is stocked as HPLC-verified research-grade lyophilised powder , see the product page.

Tirzepatide . Dual GLP-1/GIP receptor engagement

Tirzepatide is a 39-amino acid synthetic peptide with structural features derived from both GIP and GLP-1. It engages both receptor systems, with slightly higher potency at GIPR than at GLP-1R in most published receptor pharmacology.

Key research distinctions vs Semaglutide:

• Adds GIP receptor pathway affecting adipose tissue biology, insulin sensitivity and central appetite through a different circuit
• Combined pathway activation has been associated with different metabolic effects in animal models than either receptor engaged alone
• Different pharmacokinetic profile , half-life and steady-state kinetics differ from Semaglutide in preclinical models

See our Tirzepatide Ireland reference and the product page.

Retatrutide triple receptor engagement

Retatrutide adds glucagon receptor (GCGR) engagement to the GLP-1/GIP dual mechanism. The addition of GCGR agonism engages hepatic glucose output and energy expenditure pathways not activated by mono or dual agonists.

Key research distinctions:

• Engages hepatic energy expenditure via GCGR a fundamentally different pathway from insulin secretion
• Preclinical models suggest additive or synergistic effects across the three receptor systems
• Currently the most active area of metabolic peptide research literature

See our Retatrutide Ireland reference and the product page.

Choosing a compound for a research protocol

Semaglutide is the right choice when:

• The research question is specifically about GLP-1 receptor pharmacology in isolation
• You need to compare with the largest existing literature base for benchmark purposes
• Reference-standard compound for translational metabolic research

Tirzepatide is the right choice when:

• You’re studying combined GLP-1/GIP receptor engagement
• The research protocol involves adipose tissue biology or GIP-specific mechanisms
• Comparison is between mono and dual receptor engagement effects

Retatrutide is the right choice when:

• The protocol includes hepatic energy expenditure or glucagon-pathway biology
• You’re studying the current-generation triple agonist frontier
• The research is looking at receptor pharmacology at the edge of the class

Adjacent research compounds worth knowing

• Cagrilintide — amylin analogue often co-formulated with Semaglutide in research protocols
• Mazdutide dual GLP-1 / glucagon receptor agonist (a different dual profile from Tirzepatide)
• Survodutide . Dual GLP-1 / glucagon receptor agonist, another emerging research target

All available in the metabolic research peptide category.

Compliance and regulatory context

All three compounds are the current focus of HPRA enforcement in Ireland , with see our HPRA regulations guide. When ordering, ensure product pages, labelling and delivery documentation are consistent about in-vitro research-only positioning.

Continue on the topic

• Semaglutide Ireland , Research Reference
• Tirzepatide Ireland : Research Reference
• Retatrutide Ireland Research Reference
• Fat Loss research peptides category
• HPRA regulations and research peptides

All compounds supplied by Peptides Lab Ireland are for in-vitro laboratory research and educational use only. Not intended for human, veterinary or therapeutic use.