Wegovy and GLP-1: what kind of medicine is it, and how does it work?

What exactly is a GLP-1 receptor agonist, and why does it matter for weight?

GLP-1 stands for glucagon-like peptide-1, a hormone your gut releases naturally when you eat. It travels to the brain and signals that you are full; it also nudges the pancreas to manage blood sugar, and it slows gastric emptying so the stomach takes longer to hand food to the small intestine. In people living with obesity, these signals are often weaker or shorter-lived than they need to be.

A GLP-1 receptor agonist is a medicine designed to replicate that hormone and hold the receptor active for much longer than the natural version would. Semaglutide (the molecule in Wegovy) is structured to resist the enzyme that normally clears GLP-1 from the bloodstream in minutes, which is how a single weekly injection can sustain the effect across seven days. The result, for many people, is a quieter appetite and a reduced drive to eat between meals. There is a common idea that these medicines simply suppress hunger mechanically, like a plug in a drain. It is a little more nuanced: the brain regions involved regulate reward and satiety together, which is partly why the effect on cravings can feel quite different from ordinary dieting.

For a fuller look at whether semaglutide qualifies as a GLP-1 receptor agonist and what that classification means in practice, the pharmacology is covered in more detail there. The NHS medicines page for semaglutide is also a reliable starting point for patient-level information.

How is Wegovy licensed and used in the UK?

Wegovy is licensed by the MHRA for weight management in adults, used alongside a reduced-calorie diet and increased physical activity. The standard eligibility thresholds from the prescribing information are a BMI of 30 or above, or a BMI of 27 to 29.9 alongside at least one weight-related condition, for example, high blood pressure, type 2 diabetes, high cholesterol, or obstructive sleep apnoea. Lower thresholds apply for some ethnic backgrounds under UK guidance.

Treatment starts at a low dose of 0.25 mg weekly, not because this dose is therapeutic but because it gives the body time to adjust before stepping up. The prescriber titrates the dose roughly every four weeks, through 0.5 mg, 1.0 mg, 1.7 mg, and up to the standard maintenance dose of 2.4 mg. As of April 2026, a dedicated 7.2 mg single-dose pen has also been approved by the MHRA for adults with a BMI of 30 or above, extending the ceiling for people who need it.

NICE has appraised Wegovy under technology appraisal guidance TA875, recommending it within specialist weight management services for adults meeting specific criteria, for a maximum of two years. Private prescribing follows the licensed SmPC criteria rather than NHS commissioning rules, so the route to access and the eligibility picture look different depending on whether you go through the NHS or a regulated private service. The Wegovy overview page sets out both routes clearly.

What do clinical trials tell us about Wegovy as a GLP-1 medicine?

The STEP 1 trial (published in the New England Journal of Medicine and involving over 1,900 adults with obesity or overweight and at least one weight-related condition) found that participants taking semaglutide 2.4 mg weekly achieved an average weight reduction of around 15% over 68 weeks, compared with about 2.4% with placebo, alongside lifestyle support. That figure has become the reference point most people cite when asking what Wegovy can do. The STEP 1 paper is publicly accessible if you want to read the methodology yourself.

Individual results vary, and clinical trials measure averages across a large group, some participants lost considerably more, others less. Factors like dose reached, adherence, diet quality, and underlying health conditions all influence outcomes. What the evidence does show consistently is that GLP-1 receptor agonists produce meaningful weight reduction in people who tolerate them well and stay on treatment, in a way that lifestyle changes alone rarely achieve for most people with clinical obesity.

If you are curious how Wegovy's results compare with tirzepatide (a dual GIP and GLP-1 agonist) the weight-loss treatment overview gives a balanced summary. For questions about what happens when the medicine seems to stop working over time, the Wegovy plateau page addresses that pattern specifically.

What side effects come with a GLP-1 medicine like Wegovy?

Because semaglutide slows gastric emptying and affects gut motility, the most common side effects are gastrointestinal: nausea, vomiting, diarrhoea, constipation, indigestion, and bloating. These are typically at their most noticeable when you start or increase the dose, and for many people they ease within a week or two as the body adjusts. If you are specifically wondering about nausea-related symptoms, our page on Wegovy shakes looks at that experience in more detail. Drinking plenty of water and eating smaller, lower-fat meals can help.

Less commonly, people experience fatigue, headache, dizziness, or injection-site reactions. Acute pancreatitis is a less frequent but serious possibility: if you develop severe stomach pain that spreads to the back (with or without vomiting) you should seek urgent medical attention rather than waiting to see if it passes. The MHRA highlighted this in a Drug Safety Update in January 2026. Any suspected side effect can be reported directly through the Yellow Card scheme, which helps regulators monitor medicines in real-world use.

Wegovy is not recommended during pregnancy, while breastfeeding, or if you are actively trying to conceive. It is not licensed for anyone under 18. People with a history of medullary thyroid carcinoma or MEN2 syndrome, or who have had pancreatitis, should discuss their history with a prescriber before starting. These are not exhaustive contraindications, a full clinical review will cover your individual situation. If you have questions about any of this, the nume FAQs cover several common safety queries, and our support team is available seven days a week. For anyone ready to explore whether Wegovy could be appropriate for them, a free consultation with our prescribers is the right first step.