From dual to triple agonism — a brief account of where the metabolic peptide research space currently stands.
The class of metabolic peptides centered on the GLP-1 receptor has moved from quiet diabetes drug to global cultural phenomenon in less than a decade. The compounds themselves have evolved alongside the public attention — from single-receptor agonists to dual agonists to, most recently, triple agonists in late-stage trials.
This is a brief, plain account of where the science stands. It is not medical advice, and the compounds discussed are sold by Lumira for research use only.
GLP-1 (glucagon-like peptide-1) is a gut hormone released after meals. It does several useful things at once: it stimulates insulin secretion in a glucose-dependent way, suppresses glucagon, slows gastric emptying, and acts on hypothalamic centers that regulate appetite. The cumulative effect is improved glucose control and reduced food intake. Native GLP-1 has a half-life of about two minutes, so the therapeutic strategy has been to design analogs with much longer half-lives that the body cannot degrade as quickly.
Semaglutide (marketed as Ozempic for diabetes, Wegovy for obesity) is a long-acting GLP-1 receptor agonist with a once-weekly dosing schedule. The STEP trial program, published in 2021, showed mean weight loss of approximately 15% over 68 weeks at the highest dose — substantially better than anything previously available pharmacologically. Cardiovascular outcome trials also showed reduced rates of major adverse events in patients with diabetes and established heart disease.
Semaglutide established the proof of concept: substantial, sustained weight loss is achievable with a peptide drug targeting appetite physiology. It is now the reference standard against which newer compounds are measured.
Tirzepatide is a single molecule that agonizes two receptors: GLP-1 and GIP (glucose-dependent insulinotropic polypeptide). GIP is another gut hormone with effects on insulin secretion, but its role in appetite regulation is more nuanced — in some contexts GIP receptor activation appears to reduce food intake, and in others to increase it. The combined effect of activating both receptors has turned out to be substantially greater than either alone.
The SURMOUNT trial program, published in 2022–2024, showed mean weight loss of approximately 21–22% at the highest tirzepatide dose over 72 weeks — a step-change from semaglutide. Glucose control in diabetes is similarly improved. Tirzepatide (marketed as Mounjaro for diabetes, Zepbound for obesity) is now widely prescribed.
Mechanistically, why two receptors beats one is still being worked out. The leading explanation is that GIP activation modulates the side-effect profile of GLP-1 — reducing nausea while preserving the appetite-suppressing benefit — allowing higher effective doses with better tolerability.
Retatrutide adds a third receptor to the mix: the glucagon receptor. Glucagon is the hormone that signals the liver to release glucose between meals — the apparent opposite of what an antidiabetic drug should do. The insight, however, is that glucagon receptor activation also increases energy expenditure, mobilizes fat, and reduces hepatic fat content. In combination with GLP-1 and GIP agonism, the glucose-raising effect of glucagon is offset by the glucose-lowering effects of the other two, and the net result is improved metabolic profile with substantially more weight loss.
The Phase 2 trial of retatrutide, published in NEJM in 2023, reported mean weight loss of approximately 24% over 48 weeks at the highest dose — with no plateau yet in sight at 48 weeks. The Phase 3 program is ongoing as of this writing, with approval anticipated in the near future.
The trajectory across these three generations is informative. Adding receptors has consistently improved outcomes. The mechanism is not just “more drug” — it is recruiting more of the body's natural metabolic regulatory systems simultaneously, which apparently produces a cleaner and more effective effect than maximizing one pathway.
It also suggests the ceiling has not yet been reached. Combinations of four or more receptor agonisms are in preclinical development. Whether the marginal benefit continues to scale, or whether diminishing returns set in, is one of the open questions of the field.
The long-term picture remains incomplete. Three questions matter most:
Lean mass preservation. All of these compounds produce substantial weight loss, but body composition data show that a meaningful fraction of the lost mass is lean tissue, not just fat. Strategies for preserving lean mass during weight loss — resistance training, protein intake, possibly combination with myostatin inhibitors — are an active area.
Discontinuation. When patients stop taking these drugs, weight typically returns over 12–24 months. The drugs are management tools, not cures. Long-term strategies for either continuous administration or maintenance after weight loss are being studied.
Side-effect profile at scale. Short-term side effects are well-characterized (nausea, GI upset, occasional gallbladder issues). Rare events and very long-term effects are still being mapped as the user base expands.
Lumira carries semaglutide (sold as Ozempic), tirzepatide in 5mg and 10mg presentations, and retatrutide in 10mg, 15mg, and 20mg presentations. All are for laboratory research use only. For specific dosing studies, the published trial protocols (STEP, SURMOUNT, the retatrutide Phase 2) are the best primary references.
This article is provided for informational and educational purposes only. Lumira Labs products are sold strictly for laboratory research use and are not for human consumption, medical use, or veterinary application. The compounds discussed are not approved by Health Canada or the FDA for any therapeutic indication. Nothing in this article should be construed as medical advice.