Comparison / GLP-1 Class
Semaglutide vs Tirzepatide vs Retatrutide: the GLP-1 class, compared.
Three generations of incretin-axis peptides — single, dual, and triple-agonist — arranged side by side. A reference guide for Canadian researchers evaluating which compounds to keep on hand.
Over the last decade the metabolic-research toolbox has expanded from a single GLP-1 receptor target to a class of three increasingly multi-receptor peptides. Semaglutide acts on one receptor; tirzepatide on two; retatrutide on three. Each successive generation widens the receptor footprint and the questions it lets researchers ask. This guide compares the three by molecular target, observed potency, structural lineage, and where each fits in a metabolic-research workflow.
Receptor activity at a glance
- Semaglutide — GLP-1 receptor agonist. Developed from the human GLP-1(7-37) sequence with two key modifications (Aib at position 8, and an Arg-to-Lys C18 fatty-acid conjugation via a γ-Glu spacer) that confer albumin-binding and extended half-life.
- Tirzepatide — dual agonist at the GIP and GLP-1 receptors. A 39-residue synthetic peptide engineered from the GIP backbone; binds GIP receptors with native-like affinity while retaining GLP-1 activity.
- Retatrutide — triple agonist at GIP, GLP-1, and glucagon receptors. Adds the glucagon-receptor arm to the dual-agonist concept, recruiting hepatic glucagon signaling to the same molecule.
Side-by-side comparison
| Compound | Receptor targets | Approx. half-life | Reference price |
|---|---|---|---|
| Semaglutide | GLP-1 only | ~165 hours | $85 CAD (10 mg) |
| Tirzepatide | GIP + GLP-1 | ~120 hours | Not carried — reference only |
| Retatrutide | GIP + GLP-1 + glucagon | ~6 days | $60 CAD (5 mg) |
Half-life figures are from published pharmacokinetic studies in humans and may differ in in-vitro and animal models. All Pure North reference standards are lyophilized; storage at −20 °C is recommended for long-term use.
Why receptor breadth matters
GLP-1 receptor signaling alone (semaglutide) recapitulates the incretin effect on insulin secretion and slows gastric emptying. Adding the GIP receptor (tirzepatide) recruits a second incretin arm that, on its own, would oppose GLP-1 in some contexts — but in dual-agonist form appears to sensitize adipose tissue and amplify the satiety signal. Adding the glucagon receptor (retatrutide) brings hepatic energy expenditure into the picture: glucagon signaling drives lipolysis and ketogenesis. In comparative research, the practical question is whether the additional receptor arm produces a proportional readout in the model of interest, or whether the dominant signal still comes from the GLP-1 arm.
Structural lineage
Semaglutide is essentially native GLP-1(7-37) with the Aib-8 substitution to block DPP-4 cleavage plus a fatty-acid tail for albumin binding — a relatively minimal modification of a human peptide. Tirzepatide breaks more sharply from human GLP-1 because its scaffold is GIP, with carefully designed substitutions that confer GLP-1 receptor binding. Retatrutide is the most engineered of the three: a synthetic 39-residue scaffold tuned to bind three distinct receptors in a single molecule. Each compound's purity profile and impurity signatures differ accordingly — a Janoshik COA for retatrutide should be read alongside reference chromatograms, since common synthesis-byproduct peaks may not match those of semaglutide.
Storage and handling
The compounds Pure North Peptides supplies in this class (Semaglutide and Retatrutide) ship as lyophilized powder, sealed under nitrogen. Recommended storage: −20 °C, desiccated, protected from light. After reconstitution with bacteriostatic water, store the working solution at 4 °C and use within 28 days. Semaglutide is stable through multiple freeze-thaw cycles in solution; retatrutide, the most heavily modified of the three, is more sensitive — aliquot before freezing and avoid repeat thaws. See the peptide storage guide for protocol detail. Tirzepatide is included here for class comparison only and is not in our catalog.
Research workflow notes
- For comparative assay work, keep aliquots of all three at the same nominal concentration (e.g. 1 mg/mL post-reconstitution) so dose-response runs across the class don't need separate dilution series.
- Confirm identity with the lot-specific Janoshik COA before any cross-compound experiment. HPLC purity floors at Pure North Peptides are ≥ 99% on the certificate; double-check the lot-number printed on the vial against the published lab-results archive.
- Solubility differs across the class. Semaglutide and tirzepatide reconstitute cleanly in bacteriostatic water at typical research concentrations. Retatrutide can need gentle warming or extended dissolution time at higher concentrations.
FAQ
Are semaglutide, tirzepatide, and retatrutide interchangeable in research?
No. They're structurally distinct molecules with different receptor profiles. They share metabolic-axis relevance but produce different downstream signatures and should not be substituted one for the other in protocol design.
Which one has the longest half-life?
Retatrutide, at roughly 6 days in human PK studies, exceeds both semaglutide (~165 hours, about 7 days) and tirzepatide (~5 days). Semaglutide and retatrutide are close; tirzepatide is the shorter of the three.
Can a single research stack work with all three?
For comparative receptor-pharmacology work, yes — reference standards of all three are useful to keep on hand. For protocol-design questions where you're testing a hypothesis about a single receptor arm, you'd typically pair the compound with a target-specific knockout or selective antagonist rather than mixing the three.
How do I verify lot identity?
Every Pure North Peptides vial ships with a lot number printed on the label. Cross-reference that lot number against the Janoshik chromatogram published at purenorthpeptides.com/lab-results/. Identity is confirmed by LC-MS; purity by reverse-phase HPLC.
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