In under a decade the incretin peptide class has moved from a niche corner of endocrinology to the most heavily studied territory in modern metabolic research. Three peptides now define the current generation: Semaglutide, a selective GLP-1 receptor agonist; Tirzepatide, a dual GIP/GLP-1 agonist; and Retatrutide, a triple GLP-1 / GIP / glucagon agonist.
They are often lumped together as "GLP-1 peptides," but the receptor coverage, potencies, and downstream biology diverge in ways that matter for study design. This guide walks through what each compound is, how they compare, and how to think about them from a research perspective.
The incretin system in one paragraph
Incretins are gut-derived hormones released after a meal that potentiate glucose-stimulated insulin secretion. GLP-1 (glucagon-like peptide-1) and GIP (glucose-dependent insulinotropic polypeptide) are the two dominant incretins in humans. Both act through G-protein-coupled receptors on pancreatic beta cells, and both also have significant activity in the brain, adipose tissue, and gastrointestinal tract. Modern incretin peptides are engineered analogues that resist rapid degradation by DPP-4 and stretch the natural signalling window from minutes to days.
Semaglutide — selective GLP-1 agonism
Semaglutide is a long-acting GLP-1 receptor agonist carrying a fatty-acid modification that supports albumin binding and extends the plasma half-life from minutes into days. Its receptor profile is effectively single-target: high-affinity, selective GLP-1 activation.
- Receptor targets: GLP-1 only.
- Approximate elimination half-life: ~7 days (once-weekly research dosing).
- Prominent research applications: glucose homeostasis, insulin sensitivity, appetite regulation, and central-nervous-system effects of GLP-1 activation.
Tirzepatide — dual GIP/GLP-1 agonism
Tirzepatide is a synthetic peptide engineered to activate GLP-1 and GIP receptors from a single molecule. The dual profile is significant because GIP and GLP-1 signal through overlapping but non-identical pathways; adding GIP activity appears to amplify effects on adipose tissue and energy expenditure beyond what pure GLP-1 agonism produces in comparable models.
- Receptor targets: GLP-1 and GIP (dual agonist).
- Approximate elimination half-life: ~5 days.
- Prominent research applications: comparative incretin signalling studies, adipose-tissue metabolism, and dual-pathway insulin sensitivity research.
Retatrutide — triple GLP-1 / GIP / glucagon agonism
Retatrutide takes the multi-receptor design one step further by adding glucagon receptor activation to the GLP-1 / GIP profile. Glucagon activity is classically associated with raising blood glucose, which sounds counterproductive in a metabolic peptide — but its effects on hepatic energy expenditure and lipolysis, balanced against concurrent GLP-1 activity, have made it one of the most closely watched compounds in current metabolic research.
- Receptor targets: GLP-1, GIP, and glucagon (triple agonist).
- Approximate elimination half-life: ~6 days.
- Prominent research applications: energy expenditure and body-composition studies, hepatic lipid metabolism, and comparative multi-receptor signalling research.
The three side by side
Choosing between them for a study
Three questions usually decide which of the three fits a given protocol.
- Which pathway is the research question actually about? A study designed to isolate GLP-1 biology should use Semaglutide; multi-receptor questions call for Tirzepatide or Retatrutide, with the additional receptors becoming variables to control rather than eliminate.
- What dosing frequency does the protocol tolerate? All three are long-acting, but research schedules that involve repeated tissue sampling may prefer Tirzepatide's slightly shorter half-life to Semaglutide's.
- How closely does the study need to align with existing literature? Semaglutide has by far the largest published research corpus; Tirzepatide is well characterised; Retatrutide is the newest and still building its published record.
Bench handling — applies to all three
- All three are supplied lyophilised. Reconstitute with bacteriostatic water using the standard protocol in the dedicated reconstitution guide.
- Store lyophilised vials at −20 °C in the dark; hold reconstituted vials at 2–8 °C for up to four weeks in BAC water.
- Aliquot for long protocols. Repeated freeze-thaw cycles degrade all three peptides regardless of their in-vivo stability.
- Only source material from suppliers that publish batch-specific HPLC data at ≥99% purity — impurity load is amplified by the very long dosing intervals these peptides use.
