Wegovy vs Saxenda

Same drug class, different patient experience

Saxenda (liraglutide 3.0mg) was the first GLP-1 receptor agonist licensed in the UK for weight management. It produced meaningful weight loss — about 8% at 56 weeks in the SCALE trial — and for several years it was the only injectable GLP-1 weight-loss option available privately. Then Wegovy (semaglutide 2.4mg weekly) arrived. The mechanism is the same: both bind GLP-1 receptors in the hypothalamus, gut and pancreas, reducing appetite and slowing gastric emptying. But the trial-grade weight loss is roughly double, and the once-weekly injection is a meaningful adherence and quality-of-life upgrade.

Mounjaro (tirzepatide), a dual GLP-1/GIP agonist, has since become the front-runner for new patients in many UK clinics, producing approximately 22% weight loss at 72 weeks in SURMOUNT-1. But Wegovy vs Saxenda remains clinically relevant for patients who can't access tirzepatide, those with specific contraindications, or those already established on liraglutide.

The mechanistic point

Both medications activate the GLP-1 receptor. The clinical difference comes from pharmacokinetics:

• Liraglutide (Saxenda) has a half-life of about 13 hours. Once-daily subcutaneous injection. Steady state reached in 3 days. If you miss a dose, plasma levels drop quickly.
• Semaglutide (Wegovy) has a half-life of about 7 days. Once-weekly subcutaneous injection. Steady state reached over 4–5 weeks. A missed dose has much less impact — you can take it within 5 days of the scheduled day without disrupting the schedule.

The longer half-life of semaglutide produces more sustained GLP-1 receptor activation, which translates into more consistent appetite suppression and — in real-world data — dramatically better adherence than daily injection.

The trial-grade efficacy gap

STEP-1 (Wegovy, 2021) showed approximately 15% mean weight loss at 68 weeks vs roughly 2% with placebo. SCALE (Saxenda, 2015) showed approximately 8% mean weight loss at 56 weeks vs 2.6% with placebo. Even allowing for differences in trial design and population, the gap is real and clinically meaningful.

Side-effect profile

Both drugs cause similar GI side effects — nausea, vomiting, diarrhoea, constipation, reflux, and abdominal pain. Wegovy's 16-week titration (0.25mg → 0.5mg → 1.0mg → 1.7mg → 2.4mg) is slower than Saxenda's 5-week titration (0.6 → 1.2 → 1.8 → 2.4 → 3.0mg), which spreads side effects more gently. Total side-effect burden at maintenance dose is similar.

Where Saxenda still has a place

• Patients with severe adverse reactions to a previous weekly GLP-1 — the shorter half-life means side effects clear faster.
• Patients who need rapid dose adjustment up or down (e.g. before a planned procedure).
• Existing responders who've done well on Saxenda for years — if it's working, switching for the sake of switching adds risk without clear benefit.
• Patients with renal or hepatic dosing concerns where the shorter exposure cycle gives better control.

Switching between them

Switching from Saxenda to Wegovy: stop Saxenda, wait 2–3 days for liraglutide to clear, then start Wegovy at the standard 0.25mg/week initiation. The 16-week titration still applies; we don't 'continue at the equivalent dose' because the pharmacokinetics differ.

Switching from Wegovy to Mounjaro: similar approach. Stop Wegovy, wait one week, start Mounjaro 2.5mg weekly and follow the standard escalation.

What we'll go through in your consultation

A 30-minute consultation covers medical history, current medications, BMI (with NICE CG189 ethnicity-adjusted thresholds), baseline blood work if not already done, and a discussion of which medication is the best fit for you. We then prescribe and dispense in the same visit. Same-day starts are usually available with two hours' notice.