How Wegovy's action on appetite and metabolism actually works

Step 1: the injection and absorption into the bloodstream

Once you inject Wegovy under the skin (typically into the abdomen, thigh or upper arm) semaglutide is absorbed slowly into the bloodstream over several days. This gradual absorption is part of why the medicine works as a once-weekly injection rather than a daily one. The molecule is engineered to bind tightly to albumin, a protein naturally present in the blood, which protects it from being broken down too quickly. By the time you inject next week's dose, the previous dose is still active. That sustained presence is what differentiates semaglutide from the body's own GLP-1, which disappears from the blood within minutes of being released. If you want to understand how semaglutide acts once it reaches the bloodstream, that page explains the underlying science in detail. Semaglutide as a compound is the same active ingredient used across several medicines, the dose and licensed indication differ by product.

Step 2: binding to GLP-1 receptors in the brain and gut

GLP-1 receptors sit in several places: the hypothalamus (the brain's appetite-regulation centre), the gut wall, the pancreas and elsewhere. When semaglutide binds to hypothalamic receptors, it reduces the signals that drive hunger, specifically the drive to start eating and the urgency to keep eating. Satiety comes earlier in a meal and lasts longer afterwards. In the gut, binding to receptors in the stomach wall slows gastric emptying: food moves more gradually from the stomach into the small intestine. That alone extends the physical sensation of fullness. The combined effect on the brain and gut is more powerful than either alone, and it is why trial participants consistently reported eating less without feeling deprived. If you want to read more about the specific mode of action in more detail, that page goes deeper into the receptor pharmacology.

There is also a pancreatic effect: semaglutide stimulates insulin release in a glucose-dependent way, meaning it only prompts insulin when blood sugar is already elevated. This is clinically relevant for people with type 2 diabetes but also explains why the medicine's blood-sugar effects are mild in people without diabetes. The NHS semaglutide medicines page covers this mechanism in plain terms and is worth reading alongside your Patient Information Leaflet.

Step 3: dose titration and the body's adaptation

The prescribing schedule starts at 0.25 mg weekly. That is not a therapeutic dose in the sense of producing significant weight loss, its job is to let the body adjust to the medicine's effects before the dose increases. Most of the GI side effects people notice (nausea, queasiness, the occasional bout of loose stools) are the digestive system responding to slowed gastric emptying and the new gut-brain signals. Starting low reduces how strongly those effects hit. The dose moves up roughly every four weeks, through 0.5 mg and 1.0 mg and 1.7 mg, to the standard maintenance dose of 2.4 mg. From January 2026, the MHRA also approved a higher 7.2 mg dose for adults with obesity, the dedicated single-dose pen for 7.2 mg was approved in April 2026. Whether a higher dose is appropriate is a clinical decision made with your prescriber, not something to self-select. If you are curious about when the effects typically start to show, that is a separate question with a more nuanced answer than most people expect.

One thing our prescribers hear fairly often: people are surprised that the hunger reduction feels relatively quiet, not a dramatic switch being flipped, but a gradual shift where food just becomes less of a preoccupation. That tends to emerge more clearly at 1.0 mg and above, which is why the early weeks can feel underwhelming. Give the titration time to do its work.

What the evidence shows, and what it does not

The STEP 1 trial (a 68-week randomised study published in the New England Journal of Medicine) found that adults taking semaglutide 2.4 mg alongside lifestyle support lost an average of around 15% of their body weight, versus around 2.4% for those on placebo. That is a meaningful difference by any clinical standard. Importantly, the trial enrolled people with a BMI of 30 or above, or 27 or above with a weight-related condition, which mirrors the UK licensed eligibility. What the trial does not tell you is exactly how any individual will respond. Responses vary, and a prescriber reviews progress before every repeat prescription. For a broader comparison of what the evidence shows across different weight-loss medicines, the Wegovy overview page sets out the context. Separately, the weight-loss treatments overview explains how Wegovy sits alongside other licensed options. If you are thinking about cost as part of your decision, the Wegovy cost context page covers what private treatment typically involves and what legitimate pricing reflects. These are prescription medicines, NICE's appraisal of semaglutide for weight management (TA875) sets out the clinical evidence base that underpins the UK recommendation and is worth reading if you want the full picture.