When people search for peptides for weight loss, the compound class they are describing has a specific name in the research literature: GLP-1 receptor agonists, and the newer multi-receptor agonists built around the same mechanism. This is an account of what the published trials on those compounds actually measured — the mechanism, the numbers, and how the class is studied.
A note on framing before anything else. Everything below describes clinical research and regulatory-trial data. The compounds discussed are supplied by CompoundPlug as research chemicals for laboratory use only, are not authorized by Health Canada for human use, and nothing here is a recommendation, a protocol, or a claim that any compound should be used by any person to lose weight. It is a summary of what the science reports. See Research Use Only.
What “Weight Loss Peptides” Actually Refers To
The term is imprecise, and worth pinning down. Most peptides have nothing to do with body weight. The ones that have driven the entire field are a specific mechanistic class: incretin receptor agonists, peptides that mimic gut hormones the body releases after eating.
The founding member is GLP-1 — glucagon-like peptide-1 — a hormone released from the gut that signals satiety to the brain, slows gastric emptying, and modulates insulin. A GLP-1 receptor agonist is a peptide engineered to activate that same receptor, and to survive in the body far longer than the natural hormone, which is broken down within minutes.
Three generations of this idea have now been studied, and they differ by how many receptors each one hits:
- Single agonist — GLP-1 receptor only. Semaglutide.
- Dual agonist — GLP-1 plus GIP, a second incretin receptor. Tirzepatide.
- Triple agonist — GLP-1, GIP, and glucagon. Retatrutide.
A fourth compound, cagrilintide, is often grouped with these but works differently — it is an amylin analog, acting through a separate receptor system, and is studied both alone and combined with semaglutide.
The clear pattern across the trial data is that adding receptors has, so far, increased the measured effect. That is the whole reason the field moved from single to dual to triple agonism.
The Mechanism: Why These Peptides Affect Body Weight
The effect is not a stimulant effect and it is not a metabolic-rate effect. It is primarily an appetite and satiety effect, mediated in the brain.
GLP-1 receptors are expressed in regions of the hypothalamus and brainstem that regulate food intake. The trial authors describe the mechanism as acting on subcortical regions of the brain that regulate food intake — activating those receptors reduces hunger and increases the sense of fullness, and food intake falls as a result.
The multi-receptor compounds layer additional mechanisms on top:
- GIP (the second receptor in tirzepatide) is another incretin. The researchers note that GIP receptor expression in the brain does not fully overlap with GLP-1 receptor expression, and hypothesize that hitting both is what drives the larger effect seen with dual agonism.
- Glucagon (the third receptor in retatrutide) adds a distinct axis — glucagon receptor activation is associated with increased energy expenditure and effects on liver fat, which is a different lever from appetite alone.
This is why the compounds are studied as a graded series rather than as interchangeable options: each added receptor is a separate mechanistic hypothesis, and the trials were designed to test whether more receptors means more effect.
What the Trials Measured
These are among the most rigorously studied compounds in modern pharmacology. The headline figures below are from the primary phase 3 (and for retatrutide, phase 2 and the first phase 3) obesity trials, published in the New England Journal of Medicine. All are mean percentage change in body weight at the trial endpoint.
Semaglutide — the single agonist
The STEP program established semaglutide 2.4 mg weekly as the first of the modern GLP-1 agonists to show large, sustained weight reduction in people with obesity. In the head-to-head SURMOUNT-5 trial, semaglutide produced a mean weight reduction of 13.7% at 72 weeks — the reference point the newer compounds are measured against.
Tirzepatide — the dual agonist
In SURMOUNT-1, the phase 3 obesity trial, tirzepatide produced mean weight reductions of 16.0% at 5 mg, 21.4% at 10 mg, and 22.5% at 15 mg over 72 weeks, against 2.4% for placebo. In the direct head-to-head against semaglutide (SURMOUNT-5), tirzepatide reached 20.2% versus semaglutide’s 13.7% — the first trial to compare the two classes directly, and it favored the dual agonist.
Retatrutide — the triple agonist
The phase 2 obesity trial (Jastreboff et al., NEJM 2023, 338 participants) reported mean weight reductions at 48 weeks of 8.7% at 1 mg, 17.1% at 4 mg, 22.8% at 8 mg, and 24.2% at 12 mg, against 2.1% for placebo. At the top dose, 83% of participants achieved at least 15% weight reduction. Notably, the curve had not plateaued at 48 weeks — weight was still declining when the trial ended. The first phase 3 readout (TRIUMPH-4) subsequently reported roughly 28.7% at 68 weeks, consistent with the phase 2 trajectory continuing.
The dose-response pattern
Read as a class, the numbers form a clean progression — single agonist in the mid-teens, dual agonist around 20%, triple agonist into the mid-20s and beyond. That progression is the central finding of the field, and it is why research attention has moved steadily toward multi-receptor compounds.
What the Trials Also Measured: Adverse Effects
A research-grounded account does not stop at the efficacy numbers. Across every compound in this class, the trials report the same dominant adverse-effect profile, and it is a direct consequence of the mechanism.
Gastrointestinal effects — nausea, vomiting, diarrhea — are the most common adverse events in every trial, in every compound. They are dose-related, are generally described as mild to moderate, and are partially mitigated by starting low and escalating slowly. This is expected: the same gut-hormone signalling that reduces appetite also slows gastric emptying.
The trials also documented dose-dependent increases in heart rate, and the multi-receptor compounds are being studied for effects on liver fat and cardiovascular endpoints in ongoing trials. The full picture of any of these compounds is what the complete trial program shows — not the headline weight number alone.
Regulatory Status — Read This Carefully
This is where the distinction between clinical research and what CompoundPlug supplies matters most.
Semaglutide and tirzepatide are approved medications in Canada under specific brand names, for specific indications, available by prescription. If a person is seeking treatment, the route is a physician and a licensed pharmacy dispensing an authorized, DIN-bearing product.
Retatrutide is investigational. It has completed phase 2 and is in phase 3 trials. It is not approved anywhere for any use.
Research-grade versions of any of these compounds are not authorized products. They carry no DIN, have not been assessed by Health Canada for safety, efficacy, or quality, are not pharmaceutically equivalent to the approved drugs, and are not substitutes for a prescription medication. CompoundPlug supplies them as research chemicals for laboratory research only, and for no other purpose.
How CompoundPlug Fits
CompoundPlug supplies research-grade semaglutide, tirzepatide, retatrutide, and cagrilintide for laboratory research — each independently HPLC-tested for purity and mass-spec verified for identity, with the analysis published against the lot number rather than asserted. This matters more in this class than almost any other, because GLP-1 agonists are, by a wide margin, the most counterfeited compounds in the grey market. Verifying what is actually in the vial is the entire point.
Browse the full class on the GLP-1 Peptides category page, or read the Research Use Only position for how and why these compounds are supplied the way they are.
Frequently Asked Questions
What peptides are used for weight loss?
The compounds studied for weight loss are GLP-1 receptor agonists and the newer multi-receptor agonists built on the same mechanism: semaglutide (single agonist), tirzepatide (dual GLP-1/GIP), and retatrutide (triple GLP-1/GIP/glucagon), plus the amylin analog cagrilintide. They act primarily by reducing appetite through gut-hormone signalling in the brain. Semaglutide and tirzepatide are approved medications in Canada; retatrutide is investigational.
Which weight loss peptide showed the largest effect in trials?
In the published trial data, effect size tracks the number of receptors targeted. Semaglutide reduced mean body weight by about 13.7% at 72 weeks in the head-to-head SURMOUNT-5 trial; tirzepatide reached 20.2% in the same trial and up to 22.5% in SURMOUNT-1; retatrutide reported 24.2% at 48 weeks in phase 2, still rising, with a first phase 3 readout near 28.7% at 68 weeks. These are clinical trial figures, not outcomes claimed for any research-grade material.
How do these peptides cause weight loss?
Primarily by reducing appetite. GLP-1 receptors in the hypothalamus and brainstem regulate food intake; activating them increases satiety and reduces hunger, so food intake falls. The dual and triple agonists add GIP and glucagon receptor activity, which the researchers associate with additional appetite and energy-expenditure effects. It is an appetite mechanism, not a stimulant or metabolic-rate one.
What are the side effects reported in the trials?
Across every compound in the class, the most common adverse events are gastrointestinal — nausea, vomiting, diarrhea — dose-related, mostly mild to moderate, and partially mitigated by starting at a low dose. The trials also documented dose-dependent heart rate increases. This is a direct consequence of the gut-hormone mechanism.
Are these weight loss peptides legal in Canada?
Semaglutide and tirzepatide are approved prescription medications in Canada under specific brand names. Retatrutide is investigational and not approved anywhere. Research-grade versions of any of these are not authorized health products, carry no DIN, and are not substitutes for a prescription medicine. CompoundPlug supplies them for laboratory research only. Anyone seeking treatment should consult a physician.
This article summarizes published clinical research for informational purposes. It is not medical advice, not a recommendation, and not a claim regarding any research-grade compound. The compounds referenced are supplied for laboratory research use only and are not authorized for human use in Canada. Consult a licensed physician for any question about weight management or medication.