Semaglutide: The GLP-1 That Started It All (Ozempic, Wegovy, Rybelsus)
Semaglutide explained — the most prescribed GLP-1 receptor agonist in the world, sold as Ozempic, Wegovy and Rybelsus. Mechanism, dosing, trial results, side effects, and how it compares.
Semaglutide is the GLP-1 receptor agonist that took the class mainstream. Three brand names use the same active molecule for three purposes: Ozempic for type 2 diabetes by injection, Wegovy for chronic weight management by injection, and Rybelsus for type 2 diabetes by oral pill. A fourth — oral Wegovy — added weight- management dosing in pill form in December 2025.
Same molecule; different doses, indications, prices and insurance coverage. All four brands are here.
The molecule
| Aspect | Detail |
|---|---|
| Generic name | Semaglutide |
| Maker | Novo Nordisk |
| Class | GLP-1 receptor agonist (single receptor) |
| Half-life | ~7 days |
| First FDA approval | 2017 (Ozempic) |
Semaglutide is a peptide-based GLP-1 agonist engineered for a long half-life. It binds the GLP-1 receptor in the pancreas, brain, GI tract and elsewhere — producing the standard GLP-1 effects of appetite suppression, slowed gastric emptying, glucose-dependent insulin release and glucagon suppression.
For mechanism details, see GLP-1 receptor agonists.
The four brands
Ozempic — for type 2 diabetes
- Form: Weekly subcutaneous injection
- Doses: 0.25 / 0.5 / 1.0 / 2.0 mg
- FDA-approved: 2017
- Trial program: SUSTAIN
- A1c reduction: ~1.5-2.0 percentage points at top dose
- Weight loss (T2D trials): 8-14% body weight (off-label for weight management without T2D is common)
- Cardiovascular benefit: SUSTAIN-6 demonstrated MACE reduction in T2D patients with high CV risk
- List price: ~$968-$1,028/month
Wegovy — for chronic weight management
- Form: Weekly subcutaneous injection
- Doses: 0.25 / 0.5 / 1.0 / 1.7 / 2.4 mg (plus Wegovy HD 7.2 mg)
- FDA-approved: 2021 (chronic weight management); 2024 (CV risk reduction in obesity with CVD); 2024–25 (MASH with moderate-to- advanced fibrosis)
- Trial program: STEP (weight), SELECT (CV outcomes)
- Average weight loss: ~15% body weight at 68 weeks (STEP-1)
- List price: ~$1,349/month; NovoCare direct ~$349/month; commercial insurance + savings card as low as $25/month
Rybelsus — for T2D (oral)
- Form: Once-daily oral tablet
- Doses: 3, 7, 14 mg
- FDA-approved: 2019
- How to take: Empty stomach, first thing in the morning, with ≤4 oz water, at least 30 minutes before food/other meds
- A1c reduction: ~1.0-1.5 percentage points at top dose
- Weight loss: 6-9 lb on average — less than the injection forms
- List price: ~$999/month
Wegovy oral — for weight management (oral)
- Form: Once-daily oral tablet
- Doses: 0.25 / 0.5 / 1.5 / 4 / 9 / 14 / 25 mg
- FDA-approved: December 2025
- How to take: Same as Rybelsus — empty stomach, before food
- Average weight loss: ~13% body weight at top dose
- List price: Introductory $149-$199/month via NovoCare; $349 standard
The empty-stomach administration is the biggest practical drawback of oral semaglutide. The drug is highly susceptible to digestion by stomach acid and enzymes, so food triggers degradation before the medication is absorbed.
How semaglutide works
The same as other GLP-1 receptor agonists:
- Glucose-dependent insulin release — stimulates pancreatic beta cells when blood sugar rises
- Glucagon suppression — reduces liver glucose output
- Slowed gastric emptying — extends satiety, flattens post-meal glucose spikes
- Central appetite suppression — reduces hunger and "food noise"
Net result: lower blood sugar, reduced appetite, weight loss.
When semaglutide starts working
- Within 1-2 weeks: Reduced appetite and food noise — often noticeable within days
- Weeks 1-4 (starter dose): Modest weight loss (~2-4 lb)
- Weeks 5-20 (dose escalation): Steady weight loss, side effects flare with each dose increase
- 5-6 months: Most weight loss occurs in this window for typical responders
- 6-12 months: Continued slower loss; approaching plateau
Most patients reach the 2.4 mg target dose by week 17, after the graded titration schedule.
Side effects
Standard GLP-1 profile:
- Common (40-70%): Nausea, vomiting, diarrhea, constipation, reduced appetite, fatigue
- Less common: Reflux, injection-site reactions, hair thinning, gallbladder issues
- Rare: Pancreatitis, severe allergic reactions
- Boxed warning: Thyroid C-cell tumors (rodent data); contraindicated in personal/family history of MTC or MEN-2
For complete safety details, see GLP-1 side effects.
Semaglutide vs tirzepatide
Most asked comparison:
| Aspect | Semaglutide | Tirzepatide |
|---|---|---|
| Class | Single GLP-1 | Dual GLP-1/GIP |
| Maker | Novo Nordisk | Eli Lilly |
| Average weight loss (top dose) | ~15% | ~21% |
| Half-life | ~7 days | ~5 days |
| Approved CV benefit | Yes (Wegovy) | Suggestive, data maturing |
| Approved MASH benefit | Yes (Wegovy) | Under investigation |
| Approved OSA benefit | No | Yes (Zepbound) |
Tirzepatide produces greater weight loss on average. Semaglutide has the strongest CV evidence so far.
Cost summary
| Form | Indication | List price | With insurance + copay card | NovoCare direct |
|---|---|---|---|---|
| Ozempic | T2D | $968-$1,028 | $25 copay | N/A |
| Wegovy | Weight loss | $1,349 | $25 | $349 cash |
| Rybelsus | T2D | $999 | $25 | N/A |
| Wegovy oral | Weight loss | $349 | $25 | $149-$199 intro |
For deep cost analysis, see GLP-1 cost.
Compounded semaglutide
A US-licensed 503A pharmacy can compound semaglutide for an individual patient at significantly lower cost ($199-$299/month range). After FDA declared the shortage resolved in 2025, the compounding landscape narrowed — see compounded GLP-1.
FAQ
Is semaglutide a GLP-1? Yes — semaglutide is the most prescribed GLP-1 receptor agonist worldwide.
Is Ozempic the same as semaglutide? Same active ingredient. Ozempic is one brand of semaglutide; Wegovy and Rybelsus are others.
Which semaglutide is FDA-approved for weight loss? Wegovy (injection) and Wegovy oral (pill). Ozempic and Rybelsus are approved for diabetes; off-label use for weight loss is common.
Why can semaglutide be taken as a pill but other GLP-1s can't? Most other GLP-1 peptides degrade too quickly in the stomach. Semaglutide's pill version uses a special excipient (SNAC) that protects the peptide briefly enough for absorption — but only when taken on an empty stomach.
How much weight can you lose on semaglutide? Average weight loss is ~15% body weight on Wegovy 2.4 mg at 68 weeks. Individual results vary substantially.
This article is for educational purposes only and is not medical advice. Discuss any treatment decisions with a qualified healthcare professional.