GLP-1 drugs are the class of medicines — Ozempic, Wegovy, Mounjaro, Zepbound and the investigational retatrutide among them — that rewired obesity medicine in a few short years. They work by copying gut hormones that control appetite and blood sugar, and the newest ones produce weight loss that used to require surgery.
This is the map of the whole category: what GLP-1 actually means, how the generations differ (one receptor, two, now three), the full lineup with the trial numbers, side effects, what it costs and how to access it in Canada, and where the research-peptide market fits (and does not). Every section links to a deeper guide if you want to go further.
What GLP-1 actually means
GLP-1 stands for glucagon-like peptide-1, a hormone your gut releases when you eat. It does several useful things at once: it tells your pancreas to release insulin, it slows how fast your stomach empties, and it signals your brain that you are full. Drugs in this class are GLP-1 receptor agonists — molecules engineered to mimic that hormone but last for days instead of minutes.
The result is less hunger, smaller portions, fewer cravings and better blood sugar. First built for type 2 diabetes, these drugs turned out to cause so much weight loss that obesity became their defining use. The story since then has been a race to activate more hormone pathways at once — which is where the generations come in.
The generations: 1, 2 and 3 receptors
The simplest way to understand this whole category is to count receptors:
- One receptor (GLP-1 only): semaglutide — sold as Ozempic (diabetes) and Wegovy (obesity). The drug that started the boom.
- Two receptors (GLP-1 + GIP): tirzepatide — sold as Mounjaro (diabetes) and Zepbound (obesity). Adding the GIP receptor pushed weight loss higher.
- Three receptors (GLP-1 + GIP + glucagon): retatrutide, the investigational “triple agonist,” which added glucagon to also raise energy expenditure — and produced the biggest numbers yet.
There are variations on the theme too: amylin partners like cagrilintide (paired with semaglutide as CagriSema), and glucagon/GLP-1 duals like survodutide. But the one-two-three receptor ladder is the backbone of the category.
The entire GLP-1 revolution is really one idea repeated: add another hormone receptor, and the scale moves further. One, then two, now three.The thread connecting every drug in this guide
The full lineup
| Molecule | Brand(s) | Receptors | Status (Canada) |
|---|---|---|---|
| Semaglutide | Ozempic, Wegovy, Rybelsus (oral) | GLP-1 | Approved |
| Tirzepatide | Mounjaro, Zepbound | GLP-1 + GIP | Approved |
| Liraglutide | Saxenda, Victoza | GLP-1 (daily) | Approved (older) |
| Retatrutide | — (investigational) | GLP-1 + GIP + glucagon | Not approved |
| CagriSema | — (investigational) | GLP-1 + amylin | Not approved |
| Survodutide | — (investigational) | GLP-1 + glucagon | Not approved |
| Orforglipron | — (oral, new) | GLP-1 (small molecule) | Emerging |
Deeper dives: retatrutide vs tirzepatide vs semaglutide, survodutide, CagriSema, and what comes after Ozempic.
How they compare on weight
Average weight loss from the pivotal trials, highest doses, lines up almost exactly with the receptor count:
| Drug | Avg weight loss | Trial |
|---|---|---|
| Retatrutide | ~28.3% (80 wks) | TRIUMPH-1 (Phase 3) |
| Tirzepatide | ~20.9% (72 wks) | SURMOUNT-1 |
| Semaglutide | ~14.9% (68 wks) | STEP-1 |
| Tirzepatide vs semaglutide | 20.2% vs 13.7% | SURMOUNT-5 (head-to-head) |
| Liraglutide | ~8% (daily) | SCALE |
The direct head-to-head (SURMOUNT-5) is the cleanest proof: tirzepatide clearly out-loses semaglutide. Retatrutide, still investigational, sits above both. For the branded version of that rivalry see Mounjaro vs Ozempic and Wegovy vs Zepbound.
The pills are coming
Injections defined the first wave, but oral GLP-1 is the next frontier — no needles, easier to scale. Oral semaglutide (the Wegovy pill) and the new small-molecule orforglipron are the leading examples. They tend to produce somewhat less weight loss than the strongest injectables so far, but convenience could make them the mass-market option. See the Wegovy pill and orforglipron.
Side effects of the class
Because these drugs share a mechanism, they share a side-effect profile. The common ones are gastrointestinal — nausea, vomiting, diarrhoea, constipation and reflux — worst while the dose is being raised and easing over time. Most people tolerate them; a minority stop because of them.
The rarer but serious considerations include pancreatitis, gallbladder problems, and a class warning about a type of thyroid tumour seen in rodents. There are also knock-on effects of fast weight loss itself: muscle loss, facial volume loss, loose skin and temporary hair shedding. None of these is a reason to avoid the drugs, but all are reasons to use them under medical care.
Every approved GLP-1 drug is prescription-only, and dose selection, titration and monitoring are decisions for a doctor. This guide is background, not dosing guidance or a recommendation to use any specific drug.
Cost and access in Canada
In Canada these are prescription drugs dispensed through pharmacies. The practical hurdles are cost and coverage: public plans rarely cover weight-loss use, and private coverage varies, so many people pay out of pocket. Supply has also been tight, and generics are starting to arrive — a generic Ozempic and the first generic Wegovy (Sevmia) have entered the Canadian picture. For the money side, see generic Ozempic in Canada, Sevmia and weight-loss injections in Canada.
What is next
The pipeline is crowded: retatrutide’s triple-agonist Phase 3 program, CagriSema, survodutide (with strong liver-disease data), oral small molecules, and combinations aimed at protecting muscle during loss. The trajectory is clear — more potent, more convenient, and increasingly targeted at the conditions that travel with obesity, from sleep apnea to fatty liver. See retatrutide’s latest results and the full pipeline.
The research-compound angle
Several of these molecules — semaglutide, tirzepatide, retatrutide, cagrilintide — also circulate in the research-peptide market, where TrueLabs operates. It is worth stating the line plainly: a research compound is a raw material sold for in vitro and laboratory study, not the approved, dose-formulated medicine. It has no verified human dose, no sterile drug formulation and no regulatory oversight, and the trial numbers in this guide describe the pharmaceutical drugs used under medical supervision — not research vials. For sourcing and quality background, see Canadian vs imported peptides and how to read a peptide COA.
GLP-1 myths
“Myth: They all work the same.”
They share a mechanism but differ in potency. Receptor count tracks with average weight loss: three beats two beats one.
“Myth: You take them for a while and you are done.”
Trials consistently show substantial weight regain after stopping. They are treatments for a chronic condition, not a short course.
“Myth: Ozempic is a weight-loss drug.”
Ozempic is approved for type 2 diabetes. The weight-management brand of semaglutide is Wegovy. Using Ozempic for weight loss is off-label.
“Myth: Research versions are cheap equivalents of the real drug.”
No. Research compounds are unapproved raw materials for lab use, without verified dose, formulation or oversight. They are not the medicine.
For researchers
TrueLabs supplies the incretin and amylin research compounds behind this category: RT3 (retatrutide) from $90, TZ-2 (tirzepatide) from $73, and Cagrilintide from $40, in CAD for in vitro and laboratory research only. Before ordering, see how to read a peptide COA and the COA library.
FAQ
Tap a question to reveal the answer.
What are GLP-1 drugs?
Medicines that mimic the gut hormone GLP-1 to reduce appetite, slow stomach emptying and improve blood sugar. Examples include Ozempic, Wegovy, Mounjaro and Zepbound. They were built for diabetes and became the leading obesity treatments.
Which GLP-1 drug causes the most weight loss?
Among approved drugs, tirzepatide (Mounjaro/Zepbound) leads at about 20%. The investigational triple agonist retatrutide reached about 28% in Phase 3, the highest reported, but it is not yet approved.
What is the difference between Ozempic, Wegovy, Mounjaro and Zepbound?
Ozempic and Wegovy are semaglutide (diabetes and obesity brands). Mounjaro and Zepbound are tirzepatide (diabetes and obesity brands). Semaglutide hits one receptor; tirzepatide hits two.
Are there GLP-1 pills?
Yes. Oral semaglutide (the Wegovy pill) and the new small-molecule orforglipron are oral options, generally with somewhat less weight loss than the strongest injectables but far more convenience.
Do you regain weight after stopping?
Typically yes. Trials show much of the lost weight returns after stopping, which is why these are managed as long-term treatments.
What are the main side effects?
Mostly gastrointestinal — nausea, diarrhoea, constipation and reflux — worst during dose increases. Rare serious risks include pancreatitis and gallbladder problems, and the class carries a thyroid-tumour warning.
Are GLP-1 drugs covered in Canada?
Often not for weight loss. Public plans rarely cover weight-management use and private coverage varies, so many Canadians pay out of pocket. Generics are beginning to arrive.
Is retatrutide available yet?
No. As of 2026 retatrutide is investigational and not approved anywhere, despite the strongest trial results in the class.
Are research-grade GLP-1 peptides the same as the drugs?
No. Research compounds are unapproved raw materials for laboratory use, without verified dose, sterile formulation or oversight. They are not interchangeable with the prescription medicines.
Which GLP-1 drug is best for me?
That is a medical decision based on whether you are treating diabetes, obesity or both, your tolerance, cost and coverage. This guide is background for that conversation with your doctor.
Related reading
- Retatrutide vs tirzepatide vs semaglutide
- Mounjaro vs Ozempic
- Wegovy vs Zepbound
- Next weight-loss drugs after Ozempic
- Weight-loss injections in Canada
References
- Wilding JPH, et al. Once-Weekly Semaglutide in Adults with Overweight or Obesity (STEP-1). N Engl J Med. 2021;384:989-1002. NEJM
- Jastreboff AM, et al. Tirzepatide Once Weekly for the Treatment of Obesity (SURMOUNT-1). N Engl J Med. 2022;387:205-216. NEJM
- Aronne LJ, et al. Tirzepatide versus Semaglutide for the Treatment of Obesity (SURMOUNT-5). N Engl J Med. 2025. NEJM
- Jastreboff AM, et al. Triple-Hormone-Receptor Agonist Retatrutide for Obesity — A Phase 2 Trial. N Engl J Med. 2023;389(6):514-526. NEJM
- Eli Lilly / American Diabetes Association. TRIUMPH-1 Phase 3 retatrutide results, 2026. Lilly
- Health Canada. Advisory: unauthorized injectable peptide products, 2025.
This article summarizes published research and regulatory information for information only and is not medical advice. TrueLabs research compounds are sold for in vitro and laboratory research use only and are not intended for human or veterinary use.