You've heard about semaglutide — here's what it actually does

Picture the moment before you'd normally reach for a second portion

That moment, for most people, is where appetite wins over intention. Semaglutide changes the biology underneath it. It binds to GLP-1 receptors, the same receptors activated by the gut hormone GLP-1, which your body naturally releases after eating. The effect is threefold: it signals to the brain's appetite centres that you've had enough, it slows gastric emptying so food stays with you longer, and it modulates blood-sugar responses after meals.

The result, for many people on treatment, is that the pull towards eating feels genuinely quieter rather than suppressed by willpower. That's a meaningful distinction. The medicine isn't asking you to try harder; it's changing the hormonal conversation your gut is having with your brain.

Semaglutide is a single-pathway agent, targeting GLP-1 receptors only. That's worth knowing if you're comparing it with tirzepatide, which targets both GLP-1 and GIP receptors. You can read a fuller breakdown of how Wegovy works as a treatment on our dedicated page.

What the clinical trials actually showed about semaglutide

The headline figure most people encounter is around 15%. That comes from the STEP 1 trial, a large, placebo-controlled study of 1,961 adults with obesity or overweight and at least one weight-related condition, run over 68 weeks at the 2.4mg weekly maintenance dose, alongside lifestyle support. Participants who received semaglutide lost an average of about 15% of their body weight, compared with roughly 2.4% in the placebo group. The paper was published in the New England Journal of Medicine and formed a key part of the evidence base for the UK licence.

A newer development adds a higher ceiling. The MHRA approved a 7.2mg maintenance dose in January 2026, and a dedicated single-dose 7.2mg Wegovy pen on 14 April 2026. Trials at that dose reported average weight loss of around 20.7% over 72 weeks, closing the gap with the highest doses of tirzepatide. Whether the 7.2mg formulation is right for a specific person is a clinical conversation, not something to decide from a webpage.

It's also worth separating Wegovy from Ozempic. Both contain semaglutide, but Ozempic is licensed for type 2 diabetes, not weight management. Presenting or obtaining Ozempic for weight loss would be outside its UK licence. The semaglutide overview page covers that distinction in more detail.

Who semaglutide is licensed for under the UK's rules

Under the Wegovy SmPC and NICE guidance, the licensed population for private prescription includes adults with a BMI of 30 or above, or a BMI of 27 to 29.9 alongside at least one weight-related condition. Conditions that can qualify include high blood pressure, type 2 diabetes, dyslipidaemia, obstructive sleep apnoea, and cardiovascular disease. BMI thresholds are 2.5 kg/m² lower for people from South Asian, Chinese, Middle Eastern, Black African or African-Caribbean backgrounds under UK clinical guidance.

NICE's technology appraisal for semaglutide (TA875) recommends it on the NHS only within specialist weight management services, for a maximum of two years, and sets a higher BMI threshold of 35 for most people. NHS access typically involves long waiting lists. Private treatment through a regulated pharmacy is an alternative route for people who meet the licensing criteria but don't qualify for or don't want to wait for NHS provision, and a prescriber still assesses every case individually. If you're thinking about costs, our Wegovy cost page explains what a private prescription typically includes in practice.

The NICE appraisal of semaglutide is publicly available and worth reading if you want to understand the NHS framework in detail.

Side effects, safety, and the questions worth asking before you start

The side-effect profile of semaglutide is led by the gastrointestinal system. Nausea, loose stools, constipation, indigestion, and burping are the most commonly reported, particularly when starting treatment or after a dose increase. For most people these settle over days to a couple of weeks as the body adjusts, and our semaglutide 1mg dose guide explains what to expect in those earlier weeks of treatment. Fatigue and headache are also reported.

More serious but less common effects include acute pancreatitis, the MHRA has highlighted this as something to be aware of for GLP-1 medicines. Severe stomach pain that doesn't pass, particularly if it spreads to your back, warrants prompt medical attention. Gallbladder problems and signs of allergic reaction are also listed in the prescribing information, and if you're moving up through the dose schedule, our semaglutide 2mg dose page covers what the prescribing information says at that stage. The semaglutide side effects page covers the full picture, including when to contact a doctor and how to report suspected reactions.

Semaglutide is not recommended during pregnancy, while breastfeeding, or for those who are trying to conceive. It is not licensed for use in people under 18. Anyone with a history of medullary thyroid carcinoma or multiple endocrine neoplasia type 2 should not use it. These are conversations a prescriber walks through at consultation, they're not edge cases to figure out alone.

If any of the above applies to your situation and you want to talk it through, our clinical team reviews every consultation personally, the same day it's submitted. You can also visit our treatment page to start a free consultation.