Mounjaro®
Starting from £179.99/mo
Start journey Learn moreHow the mechanisms and evidence compare — and what that means for your decision
The decision you're probably trying to make
Most people land on this comparison because they've been offered, or have been taking, liraglutide, and they want to know whether semaglutide is meaningfully different or just a newer version of the same idea. That's a reasonable question. The short answer is: they share a class but not a mechanism-by-mechanism identity, and those structural differences produce measurable differences in how much weight people lose on each.
There's also a practical layer. Liraglutide (Saxenda) requires a daily injection; semaglutide (Wegovy) is once weekly. That alone changes adherence for many people. If you're considering switching from liraglutide to semaglutide, understanding why one outlasts the other in the body is a sensible starting point. The table below sets out the core comparison; the sections that follow explain what's behind the numbers.
One thing worth clearing up gently: some people assume these two medicines are interchangeable because they both say "GLP-1" on the label. They're not. The structural differences are significant enough that the licensed doses, injection frequencies, and average weight outcomes all differ. A prescriber who knows your history is the right person to weigh those differences for your specific situation.
GLP-1 receptors, half-life, and why structure matters
GLP-1 is a hormone released by the gut after eating. It tells the brain you're full, slows the speed at which the stomach empties, and nudges the pancreas to respond to blood sugar. Both liraglutide and semaglutide mimic it, but neither is identical to the natural hormone, which breaks down within minutes.
Liraglutide attaches to albumin in the blood, which extends its working life from minutes to roughly 13 hours. That's long enough for once-daily dosing, but the levels rise and fall noticeably across the day. Semaglutide takes a different approach: it binds more tightly to albumin through a longer, modified fatty-acid chain and includes structural changes that protect it from the enzyme that destroys native GLP-1. The result is a half-life of around one week. A single weekly injection keeps receptor activation steady, with far less of a peak-and-trough pattern. The NHS medicines page for semaglutide describes this mechanism in patient-level detail. Because semaglutide sits at the receptor longer, it produces more sustained appetite suppression at lower doses relative to body weight than liraglutide does at its maximum, which is part of why the trial outcomes differ as much as they do.
Tirzepatide, marketed as Mounjaro, goes a step further still by also activating GIP receptors alongside GLP-1, but that's a separate comparison. You can read about liraglutide vs semaglutide more broadly, or explore the fuller picture on the weight-loss treatment overview.
What the clinical evidence shows
The numbers here come from the landmark trials, so it's worth being direct about what they found.
| Factor | Liraglutide (Saxenda) | Semaglutide 2.4mg (Wegovy) |
|---|---|---|
| Injection frequency | Once daily | Once weekly |
| Average weight loss (trial) | ~8% at 56 weeks (SCALE trial) | ~15% at 68 weeks (STEP 1, NEJM) |
| GLP-1 receptor binding | Moderate; ~13-hour half-life | High affinity; ~7-day half-life |
| UK weight-loss licence | Yes (Saxenda brand) | Yes (Wegovy brand) |
| Available through nume | No | Yes |
The STEP 1 trial, published in the New England Journal of Medicine, enrolled 1,961 adults with obesity and found semaglutide 2.4mg produced an average body-weight reduction of around 15% over 68 weeks alongside lifestyle support. Liraglutide's SCALE trial reported roughly half that. The longer half-life and stronger receptor binding of semaglutide are believed to drive much of that difference, though study designs weren't identical, and direct head-to-head data between these two specific agents is limited. Whether semaglutide is better than liraglutide for any individual depends on more than averages.
What's licensed for weight loss in the UK right now
This section matters practically. Liraglutide remains licensed for weight management in the UK under the Saxenda brand, and it's clinically valid. nume, though, only dispenses what it can supply safely through its regulated pharmacy and clinical protocols: currently Wegovy (semaglutide) and Mounjaro (tirzepatide). Saxenda is not available through our service.
NICE has appraised semaglutide for weight management (TA875), and its guidance covers adults with a BMI of 35 or above alongside at least one weight-related condition, within specialist services on the NHS. Private prescribing through a regulated pharmacy like ours follows the licensed indications in the SmPC rather than NICE's NHS commissioning criteria, which is why access timelines and eligibility thresholds differ between the two routes. The NICE TA875 appraisal sets out the full recommendation for NHS contexts.
It's also worth naming two related medicines that cause confusion. Ozempic contains semaglutide but is licensed for type 2 diabetes, not weight management; you can read more on the Wegovy vs Ozempic page. Rybelsus is oral semaglutide, again for diabetes. Neither is a route to weight-loss treatment. If you want to understand how Wegovy's pricing sits in the current private market, the Wegovy price comparison page covers that honestly.
Which medicine suits you is a clinical decision our prescribers make with you, based on your health history, current medicines, and what you're trying to achieve. If Wegovy sounds like it might be the right fit, check your eligibility with a free consultation and a real prescriber will review your answers the same day.
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