Educational reference, not medical advice. This page summarizes information from published research and regulatory filings for educational purposes. It is not a recommendation to use any compound and should not replace guidance from a licensed healthcare provider. Most peptides discussed here are not approved for the uses described.
What it is
Semaglutide is a synthetic analog of glucagon-like peptide-1 (GLP-1), an incretin hormone the gut releases in response to food. The molecule was engineered by Novo Nordisk with two key modifications: a fatty acid side chain that binds it tightly to albumin (the most abundant blood protein), and an amino acid substitution at position 8 that protects it from the enzyme DPP-4 which normally breaks down endogenous GLP-1 within minutes. Together these changes extend the half-life from a few minutes to roughly one week, enabling once-weekly subcutaneous dosing.
It is the same active molecule under three brand names: Ozempic (subcutaneous, for type 2 diabetes), Wegovy (subcutaneous, higher doses, for weight management), and Rybelsus (oral tablet, for type 2 diabetes).
History and approval timeline
Semaglutide was developed in the 2000s as a successor to Novo Nordisk's earlier GLP-1 agonist, liraglutide (Victoza, Saxenda). The first major Phase III trials (SUSTAIN program for diabetes, STEP program for weight management) read out between 2016 and 2021.
- 2017 — FDA approves Ozempic for adults with type 2 diabetes.
- 2019 — FDA approves Rybelsus, the first oral GLP-1 agonist, for type 2 diabetes.
- 2021 — FDA approves Wegovy for chronic weight management in adults with obesity (BMI ≥ 30) or overweight (BMI ≥ 27 with at least one weight-related condition).
- 2023 — FDA expands Wegovy approval to adolescents 12+ and adds a cardiovascular risk reduction indication based on the SELECT trial.
- 2025 — Wegovy gains an indication for improving cardiovascular outcomes in adults with cardiovascular disease and obesity or overweight.
The SELECT trial in 17,604 adults without diabetes showed a 20% reduction in major adverse cardiovascular events on semaglutide compared with placebo — the first time a weight-management drug demonstrated cardiovascular benefit in a non-diabetic population.
Mechanism
GLP-1 receptors are expressed throughout the body — in pancreatic beta cells, the central nervous system, the gut, and the cardiovascular system. Semaglutide activates these receptors and the published mechanism papers describe four main effects:
- Glucose-dependent insulin secretion. Insulin is released only when blood glucose is elevated, which is why GLP-1 agonists carry low hypoglycemia risk compared with sulfonylureas.
- Suppression of glucagon. Reduces hepatic glucose output.
- Slowed gastric emptying. Food stays in the stomach longer, prolonging satiety.
- Central appetite regulation. Receptors in the hypothalamus and brainstem reduce hunger and food reward signaling.
Half-life and dosing cadence
The published terminal half-life of semaglutide is approximately 7 days, which is why a single weekly subcutaneous injection produces relatively stable plasma concentrations. Steady state is reached after roughly 4 to 5 weeks of consistent dosing.
The FDA labels for Ozempic and Wegovy specify gradual dose escalation to manage gastrointestinal side effects:
- Ozempic (T2D): Start at 0.25 mg weekly for 4 weeks → 0.5 mg → 1 mg → maintenance up to 2 mg weekly.
- Wegovy (weight management): Start at 0.25 mg weekly → escalate every 4 weeks through 0.5, 1.0, 1.7, and 2.4 mg → 2.4 mg weekly maintenance.
- Rybelsus (oral T2D): 3 mg daily for 30 days → 7 mg → up to 14 mg daily, taken on an empty stomach with no more than 4 oz of plain water.
These are the doses tested in the regulatory trials. Off-label or compounded semaglutide dosing varies but the same escalation principle applies: GI side effects are dose-dependent and proportional to escalation speed.
Reconstitution example (for compounded vials)
Branded semaglutide ships in pre-filled pens with the dose pre-set. Compounded semaglutide sold for research use is typically lyophilized in 2 mg, 4 mg, or 8 mg vials and requires reconstitution.
A 2 mg vial reconstituted with 2 mL of bacteriostatic water yields a concentration of 1 mg/mL. On a 1 mL U-100 insulin syringe, 25 units (0.25 mL) contains 0.25 mg — the typical starting dose. Vial's calculator handles the unit-to-mg conversion automatically.
What to know
- Common side effects in trials: nausea, vomiting, diarrhea, constipation, abdominal pain. Most are mild and transient during escalation.
- Boxed warning. FDA labels carry a boxed warning regarding risk of thyroid C-cell tumors based on rodent studies; the human relevance remains uncertain. Contraindicated in patients with personal or family history of medullary thyroid carcinoma or MEN 2.
- Pancreatitis. Acute pancreatitis has been reported in post-marketing data; rates in randomized trials were not significantly elevated versus placebo.
- Pregnancy. Discontinue at least 2 months before a planned pregnancy due to the long half-life.
- Storage. Pre-filled pens: refrigerate before first use, after first use store at room temperature or refrigerated for up to 56 days. Compounded lyophilized: refrigerate after reconstitution.
- Compounded versions. When the FDA placed semaglutide on its drug shortage list, compounding pharmacies were temporarily permitted to prepare it. As of October 2024 the FDA declared the shortage resolved and is actively restricting compounded versions.
Sources
- 1.Marso SP et al. (2016). Semaglutide and Cardiovascular Outcomes in Patients with Type 2 Diabetes (SUSTAIN-6). New England Journal of Medicine.
- 2.Wilding JPH et al. (2021). Once-Weekly Semaglutide in Adults with Overweight or Obesity (STEP 1). New England Journal of Medicine.
- 3.FDA Prescribing Information — Wegovy (semaglutide) injection.
- 4.FDA Prescribing Information — Ozempic (semaglutide) injection.
- 5.Lincoff AM et al. (2023). Semaglutide and Cardiovascular Outcomes in Obesity without Diabetes (SELECT). NEJM.