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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.

02How it came about

Semaglutide came out of a line of work stretching back to the 1980s, when researchers found that a hormone in the saliva of the Gila monster lizard, exendin-4, acted on the same receptor as human GLP-1 but lasted far longer. That led to exenatide, the first GLP-1 drug, approved in 2005.

Liraglutide followed in 2009, lasting about a day. Semaglutide, approved for type 2 diabetes in 2018, extended that to a week. Its weight-management licence came later, in 2021 in the US and 2023 in the UK, after trials showed the weight effect was large enough to stand as an indication of its own rather than a side effect. The tablet form for weight management arrived in the UK in July 2026.

03UK 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.

04How 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.

05What it is not

Claims that attach themselves to this compound and do not hold up.

• Not a fat burner. It does not increase metabolic rate or target fat directly. It reduces how much you eat, which is a different mechanism with different implications.
• Not licensed for cosmetic weight loss. The weight-management licence has BMI-based criteria. Wanting to be slimmer is not the same as meeting them.
• Ozempic and Wegovy are not interchangeable. Same drug, different licences, different doses, different brands. Only one is licensed for weight management.
• Not a short course. It is studied and licensed as ongoing treatment. Weight regain after stopping is the expected pattern, not a failure.

06What 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.

07Reported 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.

08Interactions and cautions

Three that matter enough to raise with a prescriber unprompted:

• Oral contraception. NHS England advises using an additional method, such as condoms, because slowed stomach emptying may affect absorption of the pill.
• Surgery and anaesthesia. Tell the anaesthetist. Delayed gastric emptying raises the risk of stomach contents entering the lungs under sedation, and guidance on pausing treatment before procedures exists for that reason.
• Other diabetes medicines. Combined with insulin or sulfonylureas, the risk of low blood sugar rises, and doses of those may need adjusting by a prescriber.

Anything taken by mouth may be absorbed differently while gastric emptying is slowed. If you take medication where the exact level matters, raise it.

09Stopping

Appetite returns and weight regain is common. Trial extensions and follow-up studies have generally found that a substantial proportion of lost weight comes back within a year or two of stopping, which is what you would expect from a drug that works by suppressing appetite while it is present.

This is the single most under-discussed fact about the whole class. It reframes the decision from a course of treatment to an ongoing one, with the cost and access questions that follow. It is worth asking about before starting rather than after.

10Monitoring

For a licensed prescription, a prescriber would typically track weight, HbA1c where diabetes is involved, kidney function, and whether side effects are tolerable. NICE requires periodic review of continued clinical benefit for weight-management prescribing, so treatment is not open-ended without review.

11Questions worth asking

Take these to a doctor or pharmacist. A good clinician will not mind being asked, and the answers are specific to you in a way nothing on this page can be.

1. Which licence am I being prescribed under, and does it match what I am hoping for?
2. What happens when I stop, and what is the plan for that?
3. How will this interact with my other medicines and my contraception?
4. What side effects mean I should contact you, rather than wait it out?
5. How often will we review whether it is still working?

12Common questions

13Sources

Links go to the authoritative source. Where a document sits behind a paywall or moves around, the full 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