GLP-1 & incretins

Semaglutide (Wegovy, Ozempic)

Reviewed 22 October 2026 · How we research

Also known as: Wegovy, Ozempic, Rybelsus, Sema

What is Semaglutide?

Semaglutide is the drug inside Wegovy (weight management), Ozempic (type 2 diabetes) and Rybelsus (a daily tablet for diabetes). It mimics the gut hormone GLP-1 and lasts about a week in the body, so the injections are given once weekly.

It was the first drug to make double-digit average weight loss routine, and the SELECT trial showed it also cuts major cardiovascular events in people with obesity and heart disease.

How Semaglutide works

Native GLP-1 is cleared within minutes. Semaglutide survives for a week because of two changes: an amino-acid swap that blocks the DPP-4 enzyme, and a C18 fatty-diacid chain that binds albumin. Once active at the GLP-1 receptor it boosts glucose-dependent insulin release, suppresses glucagon, slows gastric emptying and — most importantly for weight — acts on appetite centres in the brain to reduce hunger and food cravings.

What the research shows

STEP 1 (1,961 adults, 68 weeks): semaglutide 2.4 mg weekly produced mean weight change of −14.9% versus −2.4% on placebo.
SELECT (17,604 adults with cardiovascular disease and overweight, no diabetes): 20% relative reduction in heart attack, stroke and cardiovascular death.
STEP 1 extension: participants regained about two-thirds of the lost weight within a year of stopping.
SUSTAIN and PIONEER programmes established Ozempic and Rybelsus for type 2 diabetes.

Compare: Tirzepatide vs Semaglutide

Semaglutide side effects

Wegovy side effects are among the most-searched questions about the drug. In STEP trials:

Very common: nausea (about 44% on 2.4 mg), diarrhoea, vomiting, constipation, abdominal pain, headache, fatigue.
Common: indigestion, burping, bloating, dizziness, hair thinning during rapid weight loss, gallstones.
Rare but serious: acute pancreatitis, gallbladder inflammation, worsening diabetic retinopathy in people with existing eye disease.

Most GI symptoms are mild-to-moderate and settle within weeks of each dose step. Rodent studies showed thyroid C-cell tumours; the relevance to humans is unknown, but the drug is not used with a history of medullary thyroid cancer.

UK legal status

Semaglutide is licensed in the UK. Wegovy is recommended by NICE (TA875) for weight management within specialist NHS weight services, and is widely available on private prescription from online pharmacies. Ozempic is licensed only for type 2 diabetes; the MHRA has repeatedly warned against off-label use and counterfeit Ozempic pens.

Lyophilised semaglutide sold as a research chemical is not Wegovy or Ozempic and has no licence for human use.

More detail, including current UK research-vial prices: Semaglutide UK guide. For the doses used in published studies and the reconstitution maths: Semaglutide dosing in the literature.

Semaglutide: frequently asked questions

Is semaglutide the same as Wegovy and Ozempic?

Yes. Both contain semaglutide. Wegovy is licensed for weight management up to 2.4 mg weekly; Ozempic is licensed for type 2 diabetes up to 2 mg weekly.

How does Wegovy work?

It mimics GLP-1, a gut hormone that signals fullness. It slows stomach emptying and acts on the brain's appetite centres, so people eat less.

What are the most common Wegovy side effects?

Nausea, diarrhoea, vomiting, constipation and stomach pain. They are most frequent when the dose is increased and usually ease over a few weeks.

Is Wegovy safe?

It is a licensed medicine with large safety trials, including the 17,000-person SELECT study. Serious side effects such as pancreatitis and gallbladder disease are rare but possible, so it is prescribed with medical oversight.

What happens when you stop semaglutide?

In the STEP 1 extension, people regained about two-thirds of lost weight within a year after stopping.

References

Wilding JPH, et al. Once-weekly semaglutide in adults with overweight or obesity. N Engl J Med. 2021;384:989–1002.
Lincoff AM, et al. Semaglutide and cardiovascular outcomes in obesity without diabetes. N Engl J Med. 2023;389:2221–2232.
Wilding JPH, et al. Weight regain and cardiometabolic effects after withdrawal of semaglutide: the STEP 1 trial extension. Diabetes Obes Metab. 2022;24:1553–1564.

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