Wegovy for Weight Loss: How Semaglutide Works

What is Wegovy?

Wegovy is the brand name for a medicine called semaglutide, licensed specifically for weight management. If that ingredient sounds familiar, it should: semaglutide is the same active drug as Ozempic, which is licensed for type 2 diabetes rather than weight loss. Same molecule, different licence and different maximum dose.

Wegovy is given as a small once-weekly injection under the skin, using a pre-filled pen with a fine needle. It is a prescription-only medicine, which means a clinician reviews your health history, your BMI and any other medicines you take before deciding whether it is appropriate for you. It is not something to pick off a shelf or order without an assessment.

The science: mimicking a gut hormone

Wegovy belongs to a family of medicines called GLP-1 receptor agonists. That is a mouthful, so here is what it means in practice.

After you eat, your gut naturally releases a hormone called GLP-1 (glucagon-like peptide-1). It does two useful things: it signals to your brain that you are full, and it slows down how quickly your stomach empties. The catch is that natural GLP-1 breaks down within minutes, so its effect is fleeting.

Semaglutide is built to mimic that same hormone, but it lasts far longer, which is why one injection covers a whole week. By keeping the GLP-1 signal switched on, Wegovy does three things people notice:

1. You feel full sooner. A portion that used to disappear now feels like plenty halfway through.
2. You stay full for longer. Because your stomach empties more slowly, hunger takes longer to return.
3. "Food noise" gets quieter. Many people describe the constant mental chatter about snacks and second helpings simply fading into the background.

Think of appetite as a thermostat set too high. Wegovy turns the set-point down, so eating sensible amounts starts to feel normal rather than like a daily fight. If you want the wider picture of this whole medicine class, our guide to GLP-1 medications explained goes deeper.

How the dose builds up

You do not start on a full dose. Clinicians deliberately titrate, meaning they begin low and step the dose up gradually over several weeks. This gives your body time to adjust and keeps side effects to a minimum. Rushing the dose is the main reason people feel rough, so the slow build is a feature, not a delay.

The right target dose is not identical for everyone, which is exactly why the process is medically supervised rather than left to guesswork.

How much weight can you actually lose?

This is the number everyone wants. In the landmark STEP trials, adults with obesity who took semaglutide alongside a reduced-calorie diet and increased activity lost an average of around 15% of their body weight over 68 weeks. For someone starting at 100 kg, that is roughly 15 kg.

Two honest caveats matter here:

• Averages hide a wide range. Some people lose considerably more, others less. Your starting weight, your dose, your diet and your activity all move the needle.
• The trials included lifestyle support. Semaglutide was never tested as a magic wand you use while everything else stays the same. The results came from the medicine plus better eating and more movement working together.

Same active ingredient, different name, different licence. The details matter.

Common side effects

Most side effects of Wegovy are gastrointestinal: nausea is the most common, along with constipation, diarrhoea, indigestion and occasional vomiting. These tend to be at their strongest in the first few weeks and just after each dose increase, then usually settle as your body adjusts.

More serious reactions are less common but real, which is another reason the medicine is prescription-only and reviewed by a clinician. Anyone starting Wegovy should know which symptoms mean they need to seek advice rather than push through.

Wegovy versus Mounjaro: a fair comparison

You will often see Wegovy mentioned in the same breath as Mounjaro (tirzepatide), and it is worth understanding the difference without hype in either direction.

• Wegovy (semaglutide) targets one hormone pathway: GLP-1.
• Mounjaro (tirzepatide) targets two: GLP-1 and a second hormone called GIP.

That dual action is the headline reason Mounjaro tends to show larger average weight loss in trials. But larger on average does not mean better for every individual. Tolerance, existing health conditions, side effects and cost all feed into the decision, and some people do very well on semaglutide. The honest answer is that the right choice is individual and clinician-led, not a league table. We lay the options side by side in our guide to Mounjaro vs Ozempic vs Wegovy, and you can read how the two-hormone approach works in how Mounjaro works.

Not sure whether semaglutide or another option fits your situation? A regulated UK pharmacy can check your eligibility and, if appropriate, arrange a prescription with a proper titration plan and follow-up.

Why food and movement still matter

Because Wegovy reduces how much you eat, it is genuinely easy to under-eat protein and lose muscle along with fat, which is the opposite of what you want. Protecting muscle keeps your metabolism healthier and helps your body look toned rather than simply smaller.

The fix is not complicated: prioritise protein, keep some resistance exercise in your week, and do not skip meals just because hunger has quietened down. The medicine creates the opportunity, but your habits decide the result.

What happens if you stop

Wegovy is not a short course you take and forget. When people stop, the appetite-lowering effect fades and studies show a portion of the lost weight tends to return. That is not a personal failure, it is biology reasserting the old appetite set-point.

The people who keep the weight off are the ones who treat the medicine as a window to rebuild habits: a protein-forward way of eating, regular movement and a long-term plan agreed with their clinician.

Is Wegovy right for you?

Wegovy is powerful, and like anything powerful it is not for everyone. It is generally considered for adults living with obesity, or with excess weight plus a related health condition. It is not suitable in pregnancy, and it interacts with certain conditions and medicines.

The only way to know is a proper assessment. A regulated UK pharmacy can review your eligibility and a prescriber will tell you honestly whether semaglutide, another GLP-1 option, or a different route altogether makes the most sense for you.