GLP-1 Peptides in Canada — Semaglutide, Tirzepatide, and Retatrutide Research Context

The GLP-1 class, briefly

Glucagon-like peptide-1 (GLP-1) is an incretin hormone secreted by intestinal L-cells in response to food. It slows gastric emptying, suppresses glucagon, enhances glucose-dependent insulin secretion, and acts on hypothalamic circuits to reduce food intake. Native GLP-1 has a half-life of minutes; modern GLP-1 analogues are engineered for stability and weekly dosing.

The clinical class now spans three generations:

1. Single GLP-1 agonists — semaglutide, liraglutide, exenatide.
2. Dual GLP-1/GIP agonists — tirzepatide.
3. Triple GLP-1/GIP/glucagon agonists — retatrutide (investigational).

Semaglutide — STEP-1 and the baseline

Semaglutide is the most-studied GLP-1 analogue in human obesity research. The pivotal STEP-1 trial (Wilding et al., NEJM 2021) randomised 1,961 adults without diabetes to semaglutide 2.4 mg weekly or placebo, with lifestyle intervention in both arms. At 68 weeks, the semaglutide group lost a mean of approximately 14.9% of body weight, versus 2.4% in placebo. STEP-2, STEP-3, and STEP-4 produced convergent results across different populations and intervention designs.

In Canada, semaglutide is approved as Ozempic (type 2 diabetes) and Wegovy (chronic weight management) — both prescription-only through licensed pharmacies. Research-grade semaglutide sold by Canadian peptide vendors is not the same product, not FDA/Health Canada approved for human use, and is labelled for non-clinical research only.

Tirzepatide — SURMOUNT-1 and dual agonism

Tirzepatide is a synthetic peptide that activates both the GLP-1 and the GIP receptor. SURMOUNT-1 (Jastreboff et al., NEJM 2022) enrolled 2,539 adults with obesity without type 2 diabetes and tested 5 mg, 10 mg, and 15 mg doses against placebo over 72 weeks. The 15 mg arm produced a mean body-weight reduction of approximately 20.9%, with consistent dose- response across the lower arms.

In Canada, tirzepatide is approved as Mounjaro (type 2 diabetes) and Zepbound (chronic weight management). The mechanistic rationale for dual agonism — that GIP adds insulin-sensitising and possibly central satiety effects on top of GLP-1 — remains an active area of research.

Retatrutide — the triple agonist and Phase 2

Retatrutide (LY3437943) is an investigational triple agonist targeting GLP-1, GIP, and the glucagon receptor. The addition of glucagon receptor agonism — counter-intuitive, given glucagon's role in hepatic glucose output — appears to drive increased energy expenditure without offsetting the appetite-suppressive effects of the GLP-1 component.

The Phase 2 trial (Jastreboff et al., NEJM 2023) randomised 338 adults with obesity to retatrutide 1, 4, 8, or 12 mg weekly versus placebo over 48 weeks. The 12 mg arm produced a least-squares mean body-weight reduction of approximately 24.2% — larger than any previously reported weight-loss pharmacotherapy outcome at that timepoint. Phase 3 trials (the TRIUMPH programme) are ongoing.

Retatrutide is not approved in Canada, the United States, or any other jurisdiction as of 2026. Any material labelled "retatrutide" for sale in Canada is a research chemical, not a drug.

How the numbers compare

These are mean values in placebo-controlled trials with intensive lifestyle support. Individual response varies substantially, and the retatrutide figure is from a smaller Phase 2 dataset that may shift as Phase 3 reports.

Health Canada status, in plain terms

• Semaglutide (Ozempic, Wegovy) — approved, prescription only.
• Tirzepatide (Mounjaro, Zepbound) — approved, prescription only.
• Retatrutide — not approved, investigational.
• All non-approved analogues and research-grade material — sold in Canada as research chemicals, not drugs, for non-clinical laboratory use.

For researchers, the relevant Canadian encyclopedia entries cover the full chemistry, receptor pharmacology, and per-batch COA links.

Why the framing matters

The GLP-1 class is the most consequential peptide drug story of the last decade, and the distinction between an approved prescription drug and a research chemical has never mattered more. Trial data exist for some compounds; they don't for others. Approval exists for some; not for others. Research-use framing is how Canadian vendors stay on the right side of the Food and Drugs Act — and how Canadian researchers keep a clean audit trail.