Semaglutide is the molecule behind three of the most talked-about brand names in medicine: Ozempic, Wegovy and Rybelsus. It kicked off the GLP-1 era of metabolic drugs and remains the reference point every newer compound is measured against. Here is what it actually is, how it works, and how the three brands differ.
For how it stacks up against the dual-agonist that followed it, see tirzepatide's mechanism of action and our popular peptides overview.
What Is Semaglutide?
Semaglutide is a GLP-1 receptor agonist — a synthetic molecule that mimics glucagon-like peptide-1, a natural gut hormone released after eating. It is structurally modified so it resists rapid breakdown and lasts about a week in the body, allowing once-weekly injection (or daily oral dosing in pill form). It is made by Novo Nordisk.
How Semaglutide Works
By activating the GLP-1 receptor, semaglutide reproduces several effects of the natural hormone at once:
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Glucose-dependent insulin release: it prompts the pancreas to release insulin — but mainly when blood sugar is high, which limits the risk of hypoglycemia.
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Less glucose from the liver: it reduces glucagon, lowering the amount of sugar the liver releases.
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Slower gastric emptying: food leaves the stomach more slowly, blunting post-meal glucose spikes and prolonging fullness.
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Appetite regulation: it acts on appetite centers in the brain, reducing hunger and food intake — the main driver of weight loss.
This single-receptor (GLP-1 only) action is the key difference from newer drugs like tirzepatide, which adds a second receptor.
Ozempic vs Wegovy vs Rybelsus
All three are semaglutide — the differences are the brand, the dose, the form, and the approved use.
| Brand | Form | Primary approved use |
|---|---|---|
| Ozempic | Weekly injection | Type 2 diabetes; cardiovascular risk reduction; kidney protection in T2D |
| Wegovy | Weekly injection (and a newer oral pill) | Chronic weight management; cardiovascular risk reduction; liver disease (MASH) |
| Rybelsus | Daily oral tablet | Type 2 diabetes; cardiovascular risk reduction |
Approved Uses
Semaglutide's approvals have expanded well beyond diabetes:
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Type 2 diabetes: Ozempic (2017) and the oral Rybelsus (2019, the first oral GLP-1 drug).
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Weight management: Wegovy (2021) for adults with obesity or overweight with a related condition, later extended to adolescents 12 and older. An oral Wegovy pill (up to 25 mg) was approved in late 2025 with weight loss comparable to the 2.4 mg injection.
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Cardiovascular risk reduction: based on the SELECT trial, approved to reduce major cardiovascular events in appropriate patients.
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Kidney disease: since January 2025, Ozempic is approved to slow kidney disease progression in adults with type 2 diabetes and chronic kidney disease.
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Liver disease (MASH): since August 2025, Wegovy has accelerated approval for metabolic dysfunction-associated steatohepatitis with moderate to advanced fibrosis.
What the Trials Showed
In the STEP obesity trials, the 2.4 mg weekly dose produced average weight loss of roughly 15% over 68 weeks. In diabetes (SUSTAIN) and cardiovascular (SELECT) programs, it improved A1c and reduced cardiovascular events. These large, randomized human trials are what separate semaglutide from most research peptides, which rest on far thinner evidence.
Safety at a Glance
The most common side effects are gastrointestinal — nausea, diarrhea, vomiting and constipation — usually worst when the dose is first increased. The label carries a boxed warning for thyroid C-cell tumors based on rodent data, so it is avoided in people with a personal or family history of medullary thyroid carcinoma or MEN 2. Pancreatitis, gallbladder problems and, when combined with other diabetes drugs, low blood sugar are other considerations. It is prescription-only and should be used under medical supervision.
Legal Status
Semaglutide is an FDA-approved prescription medication, not a research chemical, and is legally available only with a prescription. For how that differs from the status of unapproved research peptides, see our guide on whether peptides are legal in the US.
Frequently Asked Questions
How does semaglutide work?
It activates the GLP-1 receptor, which increases glucose-dependent insulin release, reduces glucagon, slows stomach emptying, and reduces appetite through the brain — lowering blood sugar and driving weight loss.
What is the difference between Ozempic, Wegovy and Rybelsus?
All three are semaglutide. Ozempic is a weekly injection for type 2 diabetes, Wegovy is for weight management (injection and a newer pill), and Rybelsus is a daily oral tablet for type 2 diabetes.
Is semaglutide the same as tirzepatide?
No. Semaglutide targets only the GLP-1 receptor, while tirzepatide targets both GLP-1 and GIP. In head-to-head trials tirzepatide produced greater weight and A1c reductions.
Is semaglutide FDA approved?
Yes, across several indications including type 2 diabetes, weight management, cardiovascular risk reduction, chronic kidney disease in diabetes, and liver disease (MASH).
Disclaimer
This article is for educational and informational purposes only and is not medical advice. Semaglutide is an FDA-approved prescription medication that should be used only under the supervision of a licensed healthcare provider. The Peptide Library is an educational resource; consult your doctor before starting, stopping or changing any medication.
References
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Wegovy FDA Approval History, Drugs.com.
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Wilding JPH, et al. Once-Weekly Semaglutide in Adults with Overweight or Obesity (STEP 1). New England Journal of Medicine, 2021.
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Lincoff AM, et al. Semaglutide and Cardiovascular Outcomes in Obesity without Diabetes (SELECT). New England Journal of Medicine, 2023.