What Is Semaglutide? The Drug Behind Wegovy and Ozempic

Semaglutide is one of the most widely used GLP-1 medications in the world. Developed by Novo Nordisk, it's the active ingredient behind three brand names: Wegovy (for weight loss), Ozempic (for Type 2 diabetes), and Rybelsus (an oral tablet for diabetes). Understanding semaglutide as a single molecule sold under different names helps cut through a lot of the confusion in this space.

One molecule, three brands

All three products contain the same drug but differ in dose, formulation, and licensed use:¹²

Wegovy — semaglutide injection for weight management. Doses up to 7.2mg weekly (the highest dose was approved by the MHRA in January 2026). Licensed for adults with BMI ≥30, or ≥27 with comorbidities. Also licensed for cardiovascular risk reduction.
Ozempic — semaglutide injection for Type 2 diabetes. Doses up to 2mg weekly. Not licensed for weight loss in the UK.
Rybelsus — semaglutide in oral tablet form for Type 2 diabetes. Doses up to 14mg daily. Not licensed for weight loss in the UK (though an oral weight loss pill version launched in the US in early 2026).

How semaglutide works

Semaglutide is a GLP-1 receptor agonist — it mimics the naturally occurring gut hormone GLP-1 to suppress appetite, slow gastric emptying, and improve insulin response. What sets semaglutide apart from earlier GLP-1 drugs like liraglutide (Saxenda) is its molecular structure. It has a 94% amino acid sequence homology with natural human GLP-1, but with key modifications that make it resist enzymatic degradation and bind to albumin in the blood. This gives it a half-life of approximately 7 days — long enough for once-weekly dosing.³

Liraglutide (Saxenda), by comparison, has a half-life of only about 13 hours, which is why it requires daily injection and produces less weight loss at its approved doses.

The clinical evidence

Semaglutide has one of the most extensive clinical trial programmes of any weight loss medication:

STEP programme (weight management): A series of trials testing semaglutide at 2.4mg for obesity. The headline STEP 1 trial showed 14.9% average weight loss over 68 weeks. The STEP UP trial, testing the newer 7.2mg dose, showed 20.7% weight loss over 72 weeks.⁴⁵

SELECT trial (cardiovascular outcomes): This landmark trial of 17,604 people demonstrated that semaglutide 2.4mg reduced major adverse cardiovascular events (heart attack, stroke, cardiovascular death) by 20% in people with obesity and established cardiovascular disease. It was the first obesity medication ever to demonstrate a cardiovascular mortality benefit in non-diabetic patients, and it led to NICE recommending Wegovy for cardiovascular risk reduction in the UK.⁶

SUSTAIN programme (diabetes): Multiple trials demonstrating semaglutide's efficacy for blood sugar management in Type 2 diabetes.

Semaglutide vs tirzepatide

The main competitor to semaglutide is tirzepatide (Mounjaro), which targets both GIP and GLP-1 receptors. In the head-to-head SURMOUNT-5 trial, tirzepatide produced 20.2% weight loss compared to 13.7% for semaglutide 2.4mg. However, with the newer 7.2mg dose of Wegovy achieving 20.7%, the gap between the two drugs has narrowed significantly at their maximum doses.⁷

Semaglutide's key advantage over tirzepatide is proven cardiovascular benefit (from SELECT). Tirzepatide's cardiovascular outcomes trial is still ongoing. For a detailed comparison, see our Mounjaro vs Wegovy guide.

The oral semaglutide pill

In early 2026, an oral semaglutide pill for weight loss launched in the United States. This represents a significant development — a weight loss medication with GLP-1 efficacy that doesn't require injection. The oral version uses a technology called SNAC (sodium N-[8-(2-hydroxybenzoyl) amino] caprylate) to protect the peptide from stomach acid and enable absorption through the stomach lining.⁸

As of April 2026, the oral semaglutide weight loss pill has not yet been approved in the UK and is still being reviewed by the MHRA. If approved, it could significantly change the landscape by offering a non-injectable option with comparable weight loss to Wegovy injections.

UK access

In the UK, semaglutide for weight loss (as Wegovy) is available through Tier 3 specialist weight management services on the NHS, and through private prescriptions from regulated providers. For full eligibility details, see our eligibility checker.

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