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Semaglutide

GLP-1 receptor agonist · Ozempic, Wegovy, Rybelsus

UK status

MHRA licensed

Availability

Prescription only

Evidence base

Human RCT, phase 3

Controlled drug

No

Semaglutide is a laboratory-made copy of a hormone your gut already produces. The copy has been altered so it lasts about a week in the body instead of a few minutes. Everything it does follows from that.

01What it is

GLP-1, or glucagon-like peptide-1, is a hormone released by cells in the small intestine when food arrives. It tells the pancreas to release insulin, slows the stomach down, and signals to the brain that eating can stop. Natural GLP-1 is broken down within minutes by an enzyme called DPP-4.

Semaglutide is an analogue of that hormone, built from a chain of 31 amino acids. Structural changes at two points resist the enzyme, and an attached fatty acid chain makes the molecule bind to albumin in the blood, which keeps it circulating far longer. The result is a drug that only needs giving once a week.

02UK legal and licensing status

Semaglutide is not licensed as one product. Separate marketing authorisations cover separate brands, doses and routes, each with its own approved indication. The authoritative statement of what any one of them covers is its Summary of Product Characteristics, not marketing material and not a news article.

The tablet form for weight management is the newest of these. The MHRA approved it on 11 June 2026 and it went on sale in the UK on 6 July 2026, the first GLP-1 medicine available as a pill rather than an injection for that use. It has to be taken on an empty stomach, which is a practical constraint the injections do not have.

This is why "Ozempic for weight loss" is a phrase that causes confusion. Ozempic and Wegovy contain the same drug, but only one of them is licensed for weight management, and they are not interchangeable.

03How it works

Semaglutide binds the GLP-1 receptor, which is found in the pancreas, the stomach and the brain. Three effects follow.

• Glucose-dependent insulin release. The pancreas releases more insulin, but only when blood glucose is already raised. This is why it does not cause dangerous low blood sugar the way insulin itself can.
• Slower gastric emptying. Food stays in the stomach longer, so fullness lasts longer after a meal. This also explains most of the nausea reported early on.
• Reduced appetite signalling. Receptors in the hypothalamus are involved in how much you want to eat. Many people describe the effect as background thoughts about food quietening down.

04What the evidence shows

Figures circulating online almost all trace back to two manufacturer-funded programmes: STEP, which studied weight management, and SUSTAIN, which studied type 2 diabetes. Funding by the manufacturer does not make a trial unreliable, but it is context worth having, and it is rarely mentioned when a number gets quoted.

Read the papers themselves for the numbers. When you see a percentage quoted anywhere, check three things: the comparator group, the trial length, and whether the figure is an average or a best case.

05Reported harms

Side effects are listed in the Summary of Product Characteristics by frequency, which is the format to trust over anecdote. Gastrointestinal effects dominate the common category: nausea, vomiting, diarrhoea and constipation. Rarer signals continue to be monitored through the MHRA Yellow Card scheme, which patients can report to directly.

There are specific interactions worth knowing about because they are easy to miss. NHS England advises that people using GLP-1 medicines alongside the contraceptive pill use an additional method, since absorption may be affected, and that anyone due surgery tells their anaesthetist they are taking one.

Counterfeit product is a separate and serious risk. The MHRA has issued alerts about falsified pens, and anything bought outside a registered pharmacy cannot be assumed to contain what the label says.

06Sources

Links go to the primary source. Where a source is behind a paywall or requires registration, the citation is given so you can find it yourself.

1. Summary of Product Characteristicselectronic medicines compendium, medicines.org.uk
2. Semaglutide monographBNF
3. Technology appraisal guidanceNICE
4. STEP 1 trialNew England Journal of Medicine, 2021
5. STEP 2 trialThe Lancet, 2021
6. SUSTAIN 6 trialNew England Journal of Medicine, 2016
7. Weight management injectionsNHS England
8. Drug Safety UpdateMHRA