What Is Semaglutide? How It Works, Brands, and Who It Is For
Semaglutide is a GLP-1 receptor agonist — a drug that mimics glucagon-like peptide-1, a hormone the gut releases after eating. It increases insulin secretion when blood glucose rises, slows how quickly the stomach empties, and reduces glucagon, which together lower blood sugar and blunt appetite. It is sold under three brand names that are not interchangeable: Wegovy (weekly injection, approved for weight management), Ozempic (weekly injection, approved for type 2 diabetes) and Rybelsus (daily oral tablet). The active molecule is the same in all three; the approved use, dose ladder and formulation are not.
What semaglutide does in the body
GLP-1 is a hormone released by the intestine in response to food. It is short-lived — natural GLP-1 is broken down within minutes — which is why the body cannot sustain its effects on its own. Semaglutide is engineered to resist that breakdown, so a single weekly injection maintains GLP-1 receptor activity continuously.
Four effects follow from that, and they compound. Insulin secretion increases, but only when blood glucose is already rising, which is why semaglutide carries a low risk of hypoglycaemia on its own. Glucagon — the hormone that tells the liver to release stored glucose — falls. The stomach empties more slowly, so food stays put and fullness lasts longer. And appetite signalling in the brain shifts, which is the effect most users describe first: food simply becomes less interesting.
- Enhances insulin secretion in response to glucose spikes
- Reduces glucagon
- Slows gastric emptying
- Reduces appetite via central GLP-1 receptor signalling
The three brands, and why they are not interchangeable
All three products contain semaglutide, but they are approved for different things at different doses, and swapping between them is not a matter of matching milligrams.
Wegovy is the weight-management product and titrates to the highest dose. Ozempic is the type 2 diabetes product. Rybelsus is the oral form, taken daily rather than weekly, and its absorption depends on being taken on an empty stomach with a small sip of water — the oral formulation includes an absorption enhancer, and food defeats it.
| Brand | Route | Frequency | Dose ladder |
|---|---|---|---|
| Wegovy | Subcutaneous injection | Weekly | 0.25 → 0.5 → 1.0 → 1.7 → 2.4 mg |
| Ozempic | Subcutaneous injection | Weekly | 0.25 → 0.5 → 1 → 2 mg |
| Rybelsus | Oral tablet | Daily | 3 → 7 → 14 mg (regimen 1) |
Rybelsus has two separate regimens
The oral product is dosed on one of two ladders, and the label is explicit that they are not interchangeable. Regimen 1 runs 3 mg for 30 days, then 7 mg, then 14 mg. Regimen 2 runs 1.5 mg for 30 days, then 4 mg, then 9 mg. Moving between the two mid-course is not a supported step — a prescriber picks one.
Where semaglutide sits among the GLP-1 drugs
Semaglutide is the reference point the newer compounds are measured against. It is no longer the most effective on headline weight loss — dual and triple agonists such as tirzepatide and retatrutide report higher averages — but it has the longest record of real-world use in the group, and it is one of only two compounds in this class currently FDA-approved rather than investigational.
Frequently asked questions
This article explains what semaglutide is; it is not a guide to whether you should take it. Semaglutide carries a boxed warning — the strongest the FDA requires — based on thyroid C-cell tumours seen in rodents at clinically relevant exposures; whether that translates to humans has not been determined. It is contraindicated in anyone with a personal or family history of medullary thyroid carcinoma or with MEN 2. This page does not work through the full warnings and precautions, which a prescriber must assess against your history, and it says nothing about cost or insurance coverage, which in practice governs access more often than clinical suitability does. Compounded semaglutide sold outside the approved supply chain is not the product described here, is not covered by its safety data, and has been the subject of an FDA alert about dosing errors.
- Wegovy (semaglutide) injection — FDA prescribing information, Novo Nordisk
- Ozempic (semaglutide) injection — FDA prescribing information, Novo Nordisk
- Wegovy pen guide and dosing information — Novo Nordisk
- FDA alerts health care providers, compounders and patients of dosing errors associated with compounded injectable semaglutide products
- Semaglutide for Weight Loss: What to Expect, Month by MonthHow much weight will I lose on semaglutide, and how fast?
- Semaglutide Side Effects: What Is Common, What Is SeriousWhat are the side effects of semaglutide?
- How to Inject Semaglutide: Sites, Timing, and Pen StorageHow do you inject semaglutide?
Part of the Semaglutide Guide.