Saxenda vs Wegovy vs Mounjaro: UK Weight Loss Comparison

Saxenda, Wegovy, and Mounjaro all belong to the incretin-based therapy class, but they differ in their mechanisms, potency, and clinical profiles. Understanding these differences is the foundation for choosing the right treatment.

Saxenda (liraglutide 3mg) — Novo Nordisk - Active ingredient: Liraglutide - Class: GLP-1 receptor agonist - Approved for weight management in the UK since 2017 - Administration: Daily subcutaneous injection - Mechanism: Activates GLP-1 receptors, reducing appetite, slowing gastric emptying, and improving satiety signalling

Wegovy (semaglutide 2.4mg) — Novo Nordisk - Active ingredient: Semaglutide - Class: GLP-1 receptor agonist - Approved for weight management in the UK since 2022 - Administration: Once-weekly subcutaneous injection - Mechanism: Same GLP-1 receptor activation as Saxenda, but with a modified molecular structure that extends its half-life from approximately 13 hours (liraglutide) to approximately 7 days (semaglutide)

Mounjaro (tirzepatide) — Eli Lilly - Active ingredient: Tirzepatide - Class: Dual GIP/GLP-1 receptor agonist (first in class) - Approved for type 2 diabetes in the UK; weight management approval (as Zepbound) varies by market - Administration: Once-weekly subcutaneous injection - Mechanism: Activates both GLP-1 and GIP (glucose-dependent insulinotropic polypeptide) receptors, a dual-action approach that appears to produce superior weight loss compared to GLP-1-only agonists

The evolution from Saxenda to Wegovy to Mounjaro represents progressive improvements in both efficacy and convenience — daily to weekly dosing, and single to dual receptor targeting.

The weight loss efficacy of these three medications has been extensively studied in large clinical trials. Here is what the data shows:

Saxenda — SCALE trials: - SCALE Obesity and Prediabetes trial: 8.0% mean body weight reduction vs 2.6% with placebo over 56 weeks - Proportion achieving ≥5% weight loss: 63.2% (vs 27.1% placebo) - Proportion achieving ≥10% weight loss: 33.1% (vs 10.6% placebo) - 3,731 participants; well-established safety profile

Wegovy — STEP trials: - STEP 1 trial: 14.9% mean body weight reduction vs 2.4% with placebo over 68 weeks - Proportion achieving ≥5% weight loss: 86.4% (vs 31.5% placebo) - Proportion achieving ≥10% weight loss: 69.1% (vs 12.0% placebo) - Proportion achieving ≥15% weight loss: 50.5% (vs 4.9% placebo) - SELECT cardiovascular outcomes trial: 20% reduction in MACE (major adverse cardiovascular events)

Mounjaro — SURMOUNT trials: - SURMOUNT-1 trial (15mg dose): 22.5% mean body weight reduction vs 2.4% with placebo over 72 weeks - Proportion achieving ≥5% weight loss: 96% (vs 28% placebo) - Proportion achieving ≥10% weight loss: 85% (vs 19% placebo) - Proportion achieving ≥20% weight loss: 63% (vs 4% placebo) - SURMOUNT-2 (in type 2 diabetes): 14.7% weight loss at 15mg dose

Head-to-head comparison summary:

The data is clear — Mounjaro (tirzepatide) produces the greatest weight loss, followed by Wegovy (semaglutide), followed by Saxenda (liraglutide). The differences are clinically meaningful: - Mounjaro at maximum dose achieves approximately 50% more weight loss than Wegovy - Wegovy achieves approximately 80% more weight loss than Saxenda - Mounjaro is the only treatment where a majority of patients achieve ≥20% body weight reduction

Important caveats: These are trial averages. Individual responses vary significantly. Some patients respond exceptionally well to Saxenda and poorly to semaglutide, and vice versa. Clinical trial populations may not perfectly represent real-world patient populations.

The practical experience of taking each medication differs substantially, which matters for adherence and quality of life:

Saxenda dosing schedule: - Week 1: 0.6mg daily - Week 2: 1.2mg daily - Week 3: 1.8mg daily - Week 4: 2.4mg daily - Week 5 onwards: 3mg daily (maintenance) - Total escalation period: 4 weeks - Injection: Abdomen, thigh, or upper arm - Must be taken daily at approximately the same time - Pre-filled pen with adjustable doses

Wegovy dosing schedule: - Weeks 1–4: 0.25mg weekly - Weeks 5–8: 0.5mg weekly - Weeks 9–12: 1mg weekly - Weeks 13–16: 1.7mg weekly - Week 17 onwards: 2.4mg weekly (maintenance) - Total escalation period: 16 weeks - Injection: Abdomen, thigh, or upper arm - Once weekly, any day, with or without food - Pre-filled single-use pen per dose level

Mounjaro dosing schedule: - Weeks 1–4: 2.5mg weekly - Weeks 5–8: 5mg weekly - Subsequent escalation at 4-week intervals: 7.5mg, 10mg, 12.5mg, 15mg - Escalation above 5mg is based on individual response and tolerability - Total escalation to maximum: up to 20+ weeks - Injection: Abdomen, thigh, or upper arm - Once weekly, any day, with or without food - Pre-filled single-use pen per dose level

Practical comparison:

• •Injection frequency: Saxenda requires daily injections (365/year). Wegovy and Mounjaro require weekly injections (52/year). This is the single biggest practical difference and strongly favours the weekly options for adherence.
• •Dose escalation: Saxenda reaches maintenance in 4 weeks. Wegovy takes 16 weeks. Mounjaro takes 20+ weeks. The slower escalation reduces gastrointestinal side effects but delays full therapeutic benefit.
• •Pen convenience: All three use pen devices. Saxenda's multi-dose pen requires dose selection. Wegovy and Mounjaro use single-dose pens that are pre-set — simply attach the needle and inject.
• •Storage: All three require refrigeration before first use. Saxenda and Wegovy pens can be stored at room temperature (up to 30°C) for up to 28 days after first use. Mounjaro pens can be stored at room temperature for up to 21 days.
• •Travel: Weekly injectables are more travel-friendly than daily ones.

Gastrointestinal side effects are common across all three medications but vary in severity and frequency:

Most common side effects (all three): - Nausea - Diarrhoea - Vomiting - Constipation - Abdominal pain - Decreased appetite

Saxenda side effect profile: - Nausea: ~40% (usually transient during dose escalation) - Diarrhoea: ~20% - Constipation: ~19% - Vomiting: ~16% - Generally considered to have a milder side effect profile due to lower receptor activation intensity - Daily dosing means side effects, when they occur, are more constant but less acute

Wegovy side effect profile: - Nausea: ~44% - Diarrhoea: ~30% - Vomiting: ~24% - Constipation: ~24% - More intense GI side effects than Saxenda, particularly during dose escalation - Side effects may be more pronounced in the 24–48 hours after each weekly injection

Mounjaro side effect profile: - Nausea: ~29% (lower than Wegovy despite greater efficacy) - Diarrhoea: ~23% - Vomiting: ~12% - Constipation: ~16% - Decreased appetite: ~20% - Interestingly, despite producing more weight loss, Mounjaro's GI side effect rates are generally lower than Wegovy's in clinical trials. This may be related to the GIP receptor component, which appears to mitigate some GLP-1-related nausea.

Rare but serious risks (all three): - Pancreatitis (seek emergency care for severe abdominal pain) - Gallbladder disease (increased risk with rapid weight loss) - Thyroid C-cell tumours (observed in rodent studies; relevance to humans uncertain) - Hypoglycaemia (mainly with concurrent insulin or sulfonylurea use) - Acute kidney injury (usually secondary to dehydration from GI side effects)

Key takeaway: Mounjaro appears to offer the best tolerability-to-efficacy ratio — more weight loss with fewer GI side effects than Wegovy. Saxenda is the mildest overall but least effective. Slow dose escalation with all three medications is the most important strategy for managing side effects.

Access to these medications through the NHS is governed by NICE guidance and local commissioning decisions:

Saxenda — NHS access: - NICE approved for adults with BMI ≥35 (or ≥32.5 for certain ethnic groups) with at least one weight-related comorbidity - Must be prescribed through a specialist weight management service (Tier 3) - Treatment is typically limited to a defined duration (often 12–24 months) - If less than 5% weight loss is achieved after 12 weeks on maintenance dose, treatment should be discontinued - Availability varies by local NHS area

Wegovy — NHS access: - NICE Technology Appraisal TA875 recommended Wegovy for adults with BMI ≥35 (or ≥32.5 for certain ethnic groups) with at least one weight-related comorbidity - Must be prescribed through a specialist weight management service - Also recommended as an option for adults with BMI ≥30 with specific cardiovascular risk factors (following SELECT trial data) - Supply has been intermittent since UK launch - Local implementation of NICE guidance has been variable

Mounjaro — NHS access: - Currently licensed and available on the NHS primarily for type 2 diabetes - NICE has appraised tirzepatide for type 2 diabetes management - Weight management indication (as Zepbound) is under regulatory and NICE review for the UK - Expected to become available on the NHS for weight management, but timeline is uncertain

Private access (all three):

All three medications are available through private prescriptions in the UK. Private access removes the BMI thresholds (though responsible prescribers still apply clinical criteria), eliminates waiting lists, and provides choice of medication.

• •Private Saxenda: £150–220/month (medication only)
• •Private Wegovy: £220–300/month
• •Private Mounjaro: £250–320/month

Practical NHS access advice: 1. Start with your NHS GP — discuss your weight management goals and ask about local specialist weight management services 2. Waiting times for Tier 3 services are typically 6–18 months 3. If you have type 2 diabetes, access to GLP-1 agonists through the NHS is generally more straightforward 4. Document your weight-related comorbidities, as these strengthen eligibility 5. Keep records of previous weight management attempts, as most services require evidence of prior efforts

Choosing between Saxenda, Wegovy, and Mounjaro depends on several individual factors:

Choose Saxenda if: - You prefer to start with a well-established medication with the longest track record - Cost is a primary consideration (it is the most affordable option privately) - You do not mind daily injections - You want a gentler introduction to incretin-based therapy - You are on the NHS pathway and it is the available option

Choose Wegovy if: - You want strong weight loss efficacy with once-weekly convenience - The cardiovascular benefit data (SELECT trial) is relevant to your health profile - You prefer the established semaglutide evidence base - It is available through your NHS specialist weight management service - You have tried Saxenda and want greater efficacy

Choose Mounjaro if: - You want the maximum weight loss efficacy currently available - You are concerned about GI side effects (Mounjaro tends to be better tolerated) - You are willing to pay the premium for the most effective option - You have type 2 diabetes (dual GIP/GLP-1 mechanism offers additional glycaemic benefits) - You have tried semaglutide and want to explore an alternative mechanism

Important considerations regardless of choice:

1. Lifestyle changes are non-negotiable. All three medications work best alongside dietary improvements, regular physical activity, and behavioural support. They are tools, not replacements for healthy habits.

2. Weight regain is real. Clinical trials consistently show that weight is regained after discontinuation. Plan for long-term management, whether that means continued medication or intensive lifestyle maintenance.

3. Individual response varies. Some people respond brilliantly to one medication and poorly to another. If your first choice is not effective or well-tolerated after adequate dose escalation, switching to an alternative is reasonable.

4. Medical supervision is essential. These are prescription medications with real side effects and contraindications. Do not self-prescribe or adjust doses without medical guidance.

5. Monitor your health. Regular blood tests (HbA1c, thyroid function, renal function, liver function) should accompany treatment, regardless of which medication you choose.

*This guide is for educational purposes only. Always consult a qualified healthcare professional for personalised medical advice.*