Quick facts
- Class
- GLP-1 receptor agonist (incretin mimetic)
- Brand names
- Ozempic, Wegovy (injectable); Rybelsus (oral)
- Approved for
- Type 2 diabetes; chronic weight management
- Evidence level
- Large Phase 3 randomized trials
- Status
- FDA-approved, prescription-only
- Drug class
- GLP-1 receptor agonist (incretin mimetic)
- Half-life
- ≈1 week (enables once-weekly dosing)
- Administration
- Subcutaneous injection (oral form: Rybelsus)
- Pivotal trials
- STEP (weight), SUSTAIN (diabetes), SELECT (CV)
Key takeaways
- Semaglutide is a GLP-1 receptor agonist — one of the most clinically validated peptides in this encyclopedia, backed by large randomized trials.
- It is FDA-approved for type 2 diabetes (Ozempic, Rybelsus) and chronic weight management (Wegovy).
- It works by curbing appetite, slowing stomach emptying, and improving glucose-dependent insulin release.
- The SELECT trial showed it reduces cardiovascular events in people with overweight/obesity and existing heart disease.
- It is prescription-only; common side effects are gastrointestinal, and it carries a thyroid C-cell tumor boxed warning.
Overview
Semaglutide mimics GLP-1 (glucagon-like peptide-1), a hormone your gut releases after eating that tells the body to release insulin, feel full, and stop eating. It stands apart from most compounds on this site because it has completed large, rigorous, randomized human trials and is an approved prescription medicine.
It is sold under three brand names for two purposes: Ozempic (weekly injection) and Rybelsus (daily tablet) for type 2 diabetes, and Wegovy (weekly injection, higher dose) for chronic weight management. The active molecule is the same; the dose and indication differ.
How it works
Semaglutide engages the GLP-1 receptor across several systems:
- Appetite & satiety. It acts on appetite centers in the brain to reduce hunger and food intake — the main driver of weight loss.
- Slowed gastric emptying. Food stays in the stomach longer, increasing fullness after meals.
- Glucose-dependent insulin secretion. It boosts insulin and suppresses glucagon only when blood sugar is elevated, which lowers glucose with a low risk of hypoglycemia on its own.[1]
Clinical evidence
Semaglutide's evidence base is unusually strong for this field:
- STEP program (weight). In adults with overweight or obesity, weekly semaglutide produced mean weight loss far exceeding placebo over 68 weeks.[1]
- SUSTAIN program (diabetes). Demonstrated significant improvements in HbA1c (blood-sugar control).
- SELECT trial (cardiovascular). In people with overweight/obesity and established cardiovascular disease but without diabetes, semaglutide reduced major adverse cardiovascular events versus placebo — a landmark result extending benefit beyond weight and glucose.[2]
Dosing & side effects
Semaglutide is prescribed with gradual dose escalation over weeks to limit side effects. The most common are gastrointestinal: nausea, vomiting, diarrhea, and constipation, which often ease over time. It carries a boxed warning regarding thyroid C-cell tumors (based on rodent findings) and is contraindicated in people with a personal or family history of medullary thyroid carcinoma or MEN 2. Pancreatitis and gallbladder issues are less common considerations. It must be used under medical supervision.
Legal status
FDA-approved and prescription-only. Because of high demand, "compounded" and "research" semaglutide sold outside the regulated pharmacy supply chain has proliferated; these carry real quality, dosing, and safety concerns and are not the same as the approved product.
Semaglutide vs Tirzepatide vs Liraglutide
The three best-known incretin-based weight/diabetes peptides differ in mechanism, dosing, and typical weight loss.
| Semaglutide | Tirzepatide | Liraglutide | |
|---|---|---|---|
| Mechanism | GLP-1 agonist | GIP + GLP-1 agonist | GLP-1 agonist |
| Brands | Ozempic · Wegovy | Mounjaro · Zepbound | Victoza · Saxenda |
| Dosing | Weekly (or daily oral) | Weekly | Daily |
| Typical weight loss | High | Highest of the three | Moderate |
| CV outcome data | Yes (SELECT) | Emerging | Yes (LEADER) |
Frequently asked questions
Is semaglutide a peptide?
Yes. Semaglutide is a synthetic peptide (a modified version of the natural GLP-1 hormone) engineered to last about a week in the body.
What's the difference between Ozempic and Wegovy?
Both are semaglutide. Ozempic is approved for type 2 diabetes; Wegovy is the higher-dose version approved for weight management. The molecule is identical.
How much weight can you lose on semaglutide?
In the STEP-1 trial, average weight loss was substantially greater than placebo over 68 weeks, though individual results vary widely and depend on dose, diet, and activity.
Semaglutide vs tirzepatide — which is stronger?
In head-to-head diabetes trials and across obesity studies, tirzepatide has generally produced greater average weight loss, likely due to its dual GIP/GLP-1 mechanism. Both are highly effective.
Is compounded or 'research' semaglutide safe?
Semaglutide sold outside the regulated pharmacy supply chain is not quality-assured and carries dosing and safety risks. The approved product is prescription-only and clinician-supervised.
References
Each source links to its original record — peer-reviewed studies, regulator pages, or reference texts, labelled by type. We summarize findings neutrally; a citation is a reference, not an endorsement, and not a claim that its authors reviewed this page.
- Wilding JPH, Batterham RL, Calanna S, et al. Once-Weekly Semaglutide in Adults with Overweight or Obesity (STEP 1). N Engl J Med. 2021. Peer-reviewed study
- Lincoff AM, Brown-Frandsen K, Colhoun HM, et al. Semaglutide and Cardiovascular Outcomes in Obesity without Diabetes (SELECT). N Engl J Med. 2023. Peer-reviewed study
- Chao AM, Tronieri JS, Amaro A, et al. Semaglutide for the treatment of obesity. Trends Cardiovasc Med. 2023. Peer-reviewed study
- Smits MM, Van Raalte DH. Safety of Semaglutide. Front Endocrinol (Lausanne). 2021. Peer-reviewed study
- Davies M, Færch L, Jeppesen OK, et al. Semaglutide 2·4 mg once a week in adults with overweight or obesity, and type 2 diabetes (STEP 2): a randomised, double-blind, double-dummy, placebo-controlled, phase 3 trial. Lancet. 2021. Peer-reviewed study
- Tan HC, Dampil OA, Marquez MM. Efficacy and Safety of Semaglutide for Weight Loss in Obesity Without Diabetes: A Systematic Review and Meta-Analysis. J ASEAN Fed Endocr Soc. 2022. Peer-reviewed study