GLP-1 and metabolic medicine

Semaglutide

Also called: Ozempic, Wegovy, Rybelsus

Semaglutide is a synthetic version of the gut hormone GLP-1, made by Novo Nordisk. It is the active ingredient in Ozempic (for type 2 diabetes), Wegovy (for weight management), and Rybelsus (oral tablet for diabetes). It mimics natural GLP-1 but lasts about a week per dose instead of two minutes, which is why it is dosed weekly.

What semaglutide does in the body

Semaglutide attaches to the GLP-1 receptor on cells in the pancreas, stomach, intestines and brain. The activation triggers four main effects: insulin release in response to glucose, slowed gastric emptying, reduced appetite signalling, and lower glucagon (the hormone that raises blood sugar). The combined result is steadier blood sugar and less calorie intake, which is why the drug is approved for both diabetes and obesity.

The three brands

  • Ozempic. Once-weekly subcutaneous injection. Licensed in the UK for type 2 diabetes. Doses range from 0.25 mg to 2 mg.
  • Wegovy. Once-weekly subcutaneous injection. Licensed in the UK for chronic weight management in adults with BMI over 30 (or over 27 with weight-related comorbidity). Doses titrate to 2.4 mg.
  • Rybelsus. Daily oral tablet. Licensed in the UK for type 2 diabetes. Doses range from 3 mg to 14 mg.

How weight loss compares to other drugs

In the STEP-1 trial of Wegovy at 2.4 mg, participants lost an average of 14.9 percent of starting body weight over 68 weeks. Tirzepatide (Mounjaro) at the highest dose produced 22.5 percent in the SURMOUNT-1 trial. Older GLP-1 agonists like liraglutide produced 5 to 8 percent. Semaglutide sits in the middle of the modern GLP-1 class on weight loss but has the longest real-world track record.

Common side effects

  • Nausea, particularly in the first weeks of each dose increase. Affects 30 to 40 percent of users at higher doses.
  • Constipation. Affects roughly 1 in 5 to 1 in 4 users at full dose (around 24 percent on Wegovy at 2.4 mg in STEP-1; lower at lower doses).
  • Heartburn and reflux, related to slower stomach emptying.
  • Sulphur burps, often from food sitting longer in the stomach.
  • Fatigue, often related to lower calorie intake rather than the drug itself.
  • Hair shedding (telogen effluvium), usually a knock-on effect of rapid weight loss rather than a direct drug effect.

How it is taken in the UK

All three brands are prescription-only in the UK. Wegovy is available privately through registered pharmacies and via the NHS in specialist weight-management services with strict eligibility. Ozempic is on the NHS for type 2 diabetes. Doses titrate up over weeks to manage side effects. Stopping the drug typically returns appetite signalling to baseline, and weight regain is common unless eating habits and lean muscle mass have been protected.

Common questions

Is Ozempic the same as Wegovy?
Both contain semaglutide. Ozempic is licensed for type 2 diabetes and goes up to 2 mg per week. Wegovy is licensed for weight management and goes up to 2.4 mg per week. Wegovy uses a different injector pen and dose ladder. They are not interchangeable for licensing purposes.
How long does semaglutide stay in your body?
The half-life is around 7 days. Most of the drug is cleared after 4 to 5 weeks of stopping. Side effects ease within the first few weeks of stopping. Appetite typically returns within 2 to 6 weeks.
What's the difference between semaglutide and tirzepatide?
Semaglutide acts only on the GLP-1 receptor. Tirzepatide acts on both GLP-1 and GIP receptors. The dual mechanism produces more weight loss in trials. Side-effect profiles are similar.
Can you buy semaglutide without a prescription in the UK?
No. Semaglutide is prescription-only. Buying compounded semaglutide from unregulated sources carries real safety risk: unknown dose, unknown sterility, no manufacturer support. The MHRA has issued warnings about this.

Sources