Quick Answer
GLP-1 (glucagon-like peptide-1) receptor agonists are a class of peptides studied for their action on a natural gut hormone pathway, including gastric emptying, appetite signalling, and insulin secretion. Licensed versions include semaglutide (Ozempic, Wegovy) and tirzepatide (Mounjaro). Research analogues such as retatrutide are studied in unlicensed research contexts. In the UK, licensed GLP-1 medications require a prescription.
GLP-1 receptor agonists represent some of the most researched peptides in metabolic science. This article summarises the mechanism of action, receptor biology, and published trial data across the class.
What is GLP-1?
GLP-1 (Glucagon-Like Peptide-1) is a naturally occurring incretin hormone studied for its role in glucose metabolism and appetite signalling. GLP-1 receptor agonists are synthetic peptides designed to mimic these receptor interactions.
Key Mechanisms
- Stimulates insulin secretion in a glucose-dependent manner
- Suppresses glucagon release
- Slows gastric emptying
- Modulates appetite signalling through central nervous system pathways
- Studied for cardiovascular and neuroprotective receptor activity
The Three Main Compounds
Semaglutide (Single Agonist)
- Mechanism: Pure GLP-1 receptor agonist
- Half-life: ~7 days
Tirzepatide (Dual Agonist)
- Mechanism: GLP-1 + GIP receptor agonist
- Half-life: ~5 days
Key characteristics: dual receptor mechanism studied for combined metabolic pathway effects in trial data. Generally shows greater trial endpoint effects than single agonists. The GIP pathway adds a complementary insulin-secretion mechanism.
Retatrutide (Triple Agonist)
- Mechanism: GLP-1 + GIP + Glucagon receptor agonist
- Half-life: ~6-7 days
Key characteristics: newest and most complex receptor mechanism. The glucagon pathway adds metabolic versatility studied in trial data. Early trial data shows pronounced effects but a less established research base than the other two compounds. Full specifications, published purity results and factory-direct pricing are on the Retatrutide research page.
Comparing the Three
Trial Endpoint Hierarchy (Published Data)
- Retatrutide: largest body-weight reduction trial endpoint reported in metabolic studies
- Tirzepatide: substantial trial endpoint effects, well-studied
- Semaglutide: established trial endpoint data, most established research base
Note: differences in trial endpoint magnitude do not establish superiority for a given research application; applications vary by study design.
Adverse Events Reported in Published Trials
All three compounds show similar adverse event patterns in published trial data:
- Gastrointestinal findings (most common)
- Nausea (especially during dose-escalation phases of trials)
- Reduced appetite signalling
- Injection-site reactions
Trial design note: published trials of all GLP-1 agonists use gradual dose-escalation designs; rapid escalation is associated with markedly higher adverse event rates in the literature.
Dose-Escalation Designs in the Published Literature
Published trials of all three compounds use gradual dose-escalation designs rather than starting at maximum exposure, and report that escalation rate is the main determinant of gastrointestinal tolerability in trial cohorts. Specific amounts, schedules and escalation guidance are outside the scope of research-use-only material.
Storage & Handling
Lyophilised (Powder) Form
- Store at -20°C (freezer) for long-term storage
- Stability: 2-3 years when properly stored
- Protect from light
Reconstituted Form
- Store at 2-8°C (refrigerator); do not freeze
- Use within 28-30 days
- Protect from light (amber vials recommended)
Research Considerations by Compound
Semaglutide Research Applications
- Studies requiring the most established published research base
- Single-mechanism receptor studies
- Cost-conscious research designs
Tirzepatide Research Applications
- Dual-mechanism receptor research
- Studies examining the GIP pathway specifically
- Research models where larger trial endpoint effects are of interest
Retatrutide Research Applications
- Triple-mechanism receptor research questions
- Cutting-edge metabolic pathway research
- Studies examining glucagon-pathway receptor activity
Adverse Event Profile Across the Class
All three compounds show comparable adverse event patterns in published research settings:
- Most adverse events reported in trials are dose-dependent and transient
- Slower dose-escalation trial designs are associated with markedly fewer adverse events
- Gastrointestinal findings typically resolve within 2-4 weeks in trial cohorts
- No significant differences in trial-reported adverse event rates between the three
Research model exclusions: published trial protocols typically exclude models with a history of pancreatitis, medullary thyroid carcinoma, multiple endocrine neoplasia type 2, or severe gastrointestinal disease.
Future of GLP-1 Research
- Oral formulations under development
- Longer-acting variants under investigation
- Combination-therapy trial designs being explored
- Novel receptor targets under investigation
Conclusion
GLP-1 receptor agonists represent a significant area of metabolic research. Semaglutide offers the most established published profile, tirzepatide a dual receptor mechanism, and retatrutide a triple-agonist mechanism still progressing through clinical trials.
Administration guidance is outside the scope of research-use-only material.