Mounjaro vs Saxenda: weight-loss evidence, risks and switching
Mounjaro is a weekly injection; Saxenda is a daily injection. Tirzepatide produced larger average weight losses in the separate trials summarised below, but those studies did not compare it directly with liraglutide. The useful question is which option is appropriate, tolerable and sustainable for you—not which one wins an invented score out of ten.
This guide compares their adult weight-management use in the UK. It does not select a medicine or dose for you. Clinical suitability, NHS funding and whether a pharmacy can supply a prescription are three separate questions.
What actually differs?
| Question | Mounjaro | Saxenda |
|---|---|---|
| Active ingredient | Tirzepatide | Liraglutide |
| How it works | Acts on GIP and GLP-1 receptors | Acts on GLP-1 receptors |
| Routine | Once-weekly injection | Once-daily injection |
| Licensed adult weight-management starting criteria | BMI at least 30, or at least 27 with a weight-related condition | BMI at least 30, or at least 27 with a weight-related condition |
| A useful review question | What benefit, side effects and review plan justify continuing? | Has the adult stopping rule been assessed after 12 weeks on the 3.0 mg daily dose? |
These are product-licence details, not a promise of NHS eligibility. Both require prescribing assessment and are used alongside changes to eating and activity. [1] [2]
What do the weight-loss studies really show?
Compare the study design before comparing the headline. Both trials below enrolled adults without diabetes and included lifestyle support. Neither was a men-only trial. Their durations, participants and doses differed.
| Study | Treatment and duration | Average body-weight reduction |
|---|---|---|
| SURMOUNT-1; 2,539 adults | Tirzepatide 5, 10 or 15 mg weekly; 72 weeks | 15.0%, 19.5% and 20.9%, respectively; placebo 3.1% |
| SCALE Obesity and Prediabetes; 3,731 adults | Liraglutide 3.0 mg daily; 56 weeks | 8.0%; placebo 2.6% |
Sources: original trial publications. SURMOUNT-1 was funded by Eli Lilly; SCALE by Novo Nordisk. These are average study outcomes, not guaranteed results or starting-dose effects. [3] [4]
What you can reasonably take away: the tirzepatide results support a discussion about substantial weight reduction. What you cannot do is subtract these two trials and claim that a particular man will lose that much more after switching. A Mounjaro-versus-Wegovy trial would not answer the Mounjaro-versus-Saxenda question either.
Which routine is more workable for your life?
Put the prescription into an ordinary week. Would a daily injection be easier to attach to a routine, or would a weekly appointment with yourself be easier to remember? Who will answer questions when you feel unwell? How will you handle travel, sharps disposal and obtaining the next supply?
Ask for the total ongoing cost at the anticipated maintenance dose, including consultations, delivery and any separately charged support. A cheap first month does not tell you whether the next six months fit your budget. Ask what happens if treatment is interrupted; do not plan a restart from the dose on an old box.
Agree what success means beyond a smaller number: improved day-to-day function, a plan you can maintain, and side effects you can manage. Record questions and symptoms for your prescriber rather than treating a comparison table as a treatment plan.
Side effects and the point at which you need help
Nausea, vomiting and diarrhoea are recognised effects of these medicines; tolerability matters as well as effectiveness. Tell the prescriber about other medicines, particularly insulin or sulfonylureas, and any relevant digestive or pancreatic history. [1] [2]
Do not dismiss severe, persistent abdominal pain as an ordinary side effect. Pain that may spread to your back, with or without vomiting, needs urgent medical assessment because pancreatitis is a possible serious reaction to these injections. [5]
Contact your treating service promptly when symptoms interfere with eating, drinking or ordinary activity. Severe symptoms, collapse or an immediate threat to life require emergency help. Do not increase a dose to compensate for a disappointing week on the scales.
Switching is a clinical handover—not a dose conversion
Speak to the prescribing team before changing medicine or brand. The MHRA specifically advises discussing a switch with a healthcare professional. [6]
Before discussing a switch from Saxenda to Mounjaro, have these details ready:
- The exact product and dose you currently use.
- The date of your last injection.
- Any side effects and treatment gaps.
Ask the prescribing team for written instructions covering:
- The last dose of the old medicine and the first dose of the new one.
- Who owns the follow-up.
- What to do if you cannot tolerate the new treatment.
Do not combine these injections or invent a milligram-for-milligram conversion yourself.
For adults using Saxenda, its product information says to discontinue if at least 5% of initial body weight has not been lost after 12 weeks at 3.0 mg a day. That is not simply 12 weeks after the first starter dose. Your clinician should assess the stopping rule and alternatives. [2]
Take these questions to the prescriber
- What makes this medicine appropriate for my medical history and goals?
- What is the review point, and what would lead us to continue, change or stop?
- What is the complete ongoing cost, and who handles side effects or supply interruptions?
- Can I leave with a written handover plan rather than infer one from the internet?
Keep the support separate from the prescription
SHIFT’s Programme brings together food, movement and everyday support; My Timber can keep your own goals and treatment history in one place. Those records are not a prescription or a clinician’s approval. Use them to make the next conversation easier.
Explore the Programme · Open your Health Passport in My Timber · Check the separate NHS access routes
Common questions
Is Mounjaro better than Saxenda?
Separate trials reported greater average weight reduction with tirzepatide, but this page does not present a direct comparison trial or a personalised prediction. Suitability, adverse effects, support and affordability still matter.
Can I switch straight from Saxenda to Mounjaro?
A prescriber needs to plan the change using your current treatment, last dose, treatment gaps and tolerability. Do not overlap medicines or calculate a replacement dose yourself.
Does meeting the licence criteria mean I can get it on the NHS?
No. NHS commissioning, referral and prioritisation rules are distinct from a medicine’s licence. See the NHS pathways guide and check your local service.
Sources and editorial responsibility
- Mounjaro: UK summary of product characteristics
- Saxenda: UK summary of product characteristics
- Jastreboff et al., SURMOUNT-1, New England Journal of Medicine (2022)
- Pi-Sunyer et al., SCALE, New England Journal of Medicine (2015)
- MHRA: strengthened warnings on acute pancreatitis, 29 January 2026
- MHRA: GLP-1 medicines—what you need to know
Product information and access arrangements can change. Use the original source and your treating service for decisions about your care. How SHIFT prepares articles · Report a factual correction.
What changed on 19 September 2026: Replaced unsupported ratings and a different-drug comparison with separate-trial evidence, adult review criteria, safety advice and a practical switching checklist.