Liraglutide or semaglutide for weight loss: what the trial data actually shows

What the STEP and SCALE trials tell us about these two medicines

The clearest way to understand the difference between liraglutide and semaglutide is to look at how each performed in its pivotal phase-3 trial, because those are the studies that shaped UK licensing and prescribing.

The SCALE Obesity and Prediabetes trial tested liraglutide 3mg (Saxenda) over 56 weeks in adults with obesity or overweight plus a weight-related condition. Participants lost an average of around 8% of body weight compared with roughly 2.6% on placebo, a meaningful result, but modest by today's standards.

The STEP 1 trial, published in the New England Journal of Medicine, tested semaglutide 2.4mg (Wegovy) over 68 weeks in a similar population. Average weight loss was approximately 15%, nearly double liraglutide's figure, with about a third of participants losing 20% or more. No direct head-to-head randomised trial of the two medicines exists, so these numbers come from separate studies with different designs, a point worth being honest about. But the gap is large enough that NICE, when it appraised semaglutide, cited the substantially greater efficacy as central to its recommendation.

Once-weekly dosing is also relevant here. Liraglutide requires a daily injection; semaglutide is taken once a week. For many people the reduced injection burden matters to adherence, and adherence matters to outcomes. The differences between liraglutide and semaglutide go deeper than a dose frequency, though, their molecular half-lives and receptor binding profiles differ, which is part of why the weight-loss outcomes diverge.

What is licensed for weight loss in the UK right now

Both Saxenda (liraglutide 3mg) and Wegovy (semaglutide 2.4mg up to 7.2mg) hold UK licences for weight management in adults with a BMI of 30 or above, or 27 or above alongside a relevant health condition such as high blood pressure, type 2 diabetes or obstructive sleep apnoea. Wegovy also holds a separate licence for reducing cardiovascular event risk in eligible adults.

The NHS medicines information on semaglutide covers Wegovy's licensed indications, side effects and how it works, a practical starting point if you want the official patient-level summary. For NICE's formal appraisal, tirzepatide (Mounjaro) was also assessed; you can explore how Wegovy compares with other licensed options separately.

One distinction matters for the UK specifically: Ozempic is also semaglutide, but it is licensed for type 2 diabetes, not weight management. Rybelsus is oral semaglutide for diabetes. Neither should be sought for weight loss, the weight-loss licence belongs to Wegovy. The same logic applies to liraglutide: Victoza (liraglutide for diabetes) is not interchangeable with Saxenda for weight management purposes.

As of summer 2026, the medicines for weight loss that nume's pharmacy dispenses are Wegovy and Mounjaro (tirzepatide). If you are curious about choosing between semaglutide and liraglutide for weight loss, the evidence consistently favours semaglutide on efficacy, and it is the one available through our clinical pathway. You can review what Wegovy costs privately to understand the pricing picture before your consultation.

Side effects: how similar are liraglutide and semaglutide

Both medicines share a broadly similar side-effect profile because they act on the same receptor type. Nausea, diarrhoea, constipation, vomiting and indigestion are the most commonly reported effects across both. These tend to be most noticeable in the early weeks and around dose increases, and they often settle within a fortnight as the body adjusts.

There are some differences in how pronounced gastrointestinal effects are. Semaglutide's longer half-life means it stays active in the body for longer between doses, which some people find helps reduce the intensity of nausea, though individual responses vary considerably. Bloating and digestive symptoms on Wegovy are a common early concern that our prescribers are well practised at helping patients manage.

Both medicines carry a caution around pancreatitis: severe and persistent stomach pain reaching into the back, with or without vomiting, needs prompt medical attention, and the MHRA has highlighted this in guidance to prescribers and patients. Anyone with a history of pancreatitis should discuss this with a clinician before starting either drug. Pregnancy, breastfeeding, and plans to conceive are contraindications for both; under-18s are not licensed for either. These details are covered in the patient information leaflet that accompanies the medicine and in the clinical review every patient receives through our pharmacy.

For a broader picture of how semaglutide works and what to expect, the evidence base spans tens of thousands of participants across the STEP programme and related trials.

Which medicine is right for you, and how to take the next step

The short answer is that this is genuinely a clinical decision, not a consumer one. Trial averages describe populations; your individual health history, other medicines you take, your BMI, and any existing conditions all shape what a prescriber will recommend. The fact that semaglutide outperforms liraglutide on average weight loss does not mean it is automatically the right choice for every individual, prescribers occasionally have clinical reasons to prefer one agent over another.

At nume, every consultation is read by a GPhC-registered Independent Prescriber (a real clinician, not automated decision software) on the day you submit it. The relationship between liraglutide and semaglutide is one of the questions our team fields regularly, and the conversation about which suits you belongs inside a clinical review, not a comparison table.

If Wegovy turns out to be clinically appropriate, your pen arrives the next working day via DPD, in a plain unbranded box, tracked on your phone like any parcel, but with a cold pack inside keeping the medicine within its required storage range. Discreet and simple. For anyone ready to understand their options, checking eligibility through a free consultation is the natural next step.