Mounjaro vs Saxenda: Which Weight Loss Injection Is Right for You?
Both Mounjaro (tirzepatide) and Saxenda (liraglutide) are prescription weight loss injections licensed in the UK for chronic weight management. They work via related but distinct mechanisms, and their clinical trial results differ substantially. This guide compares them across efficacy, dosing, side effects, eligibility, and practical considerations to help you understand which may be more appropriate — a decision always made in the context of a full medical consultation.
20.9%
Average body weight loss with Mounjaro 15 mg (SURMOUNT-1)
8%
Average body weight loss with Saxenda 3 mg (SCALE Obesity)
×1/wk
Mounjaro dosing frequency
×1/day
Saxenda dosing frequency
How Each Medication Works
Understanding the mechanism of each drug helps explain the difference in their clinical outcomes.
Saxenda — Single Hormone Pathway
Liraglutide activates GLP-1 receptors in the hypothalamus and gut. It reduces appetite, slows gastric emptying, and stabilises blood sugar. Approved in the UK since 2017 with a well-established safety record.
Mounjaro — Dual Hormone Pathway
Tirzepatide activates both GIP and GLP-1 receptors simultaneously — a synergistic combination that produces more powerful appetite suppression and greater weight loss than either pathway alone. See our guide to how Mounjaro works for full detail.
The dual-agonist design of Mounjaro represents the principal pharmacological reason for its superior efficacy in clinical trials. GIP receptors are expressed in adipose tissue, the central nervous system, and the pancreas — adding the GIP pathway to GLP-1 activation amplifies the metabolic signal beyond what GLP-1 alone can achieve.
Efficacy: Head-to-Head Data
The most frequently cited comparison draws on two separate phase-3 randomised controlled trials: SURMOUNT-1 (tirzepatide) published in the New England Journal of Medicine in 2022, and SCALE Obesity (liraglutide), also published in the NEJM in 2015. These were distinct trials in different populations and cannot be interpreted as a direct head-to-head comparison. Individual results will vary.
| Outcome | Mounjaro 15 mg (SURMOUNT-1) | Saxenda 3 mg (SCALE Obesity) |
|---|---|---|
| Average body weight loss | 20.9% | 8.0% |
| Participants losing ≥10% body weight | ~89% | ~33% |
| Participants losing ≥15% body weight | ~77% | ~16% |
| Participants losing ≥20% body weight | 57% | ~6% |
| Additional weight loss vs placebo | +17.8% | +5.4% |
| Trial duration | 72 weeks | 56 weeks |
Important context: These figures come from separate clinical trials with different participant populations, trial durations, and methodologies. They are not a direct randomised comparison. Both medications were used alongside a reduced-calorie diet and increased physical activity. Individual results vary considerably.
Dosing and Administration
The dosing schedule and practical administration of the two medications differ in ways that matter to patients in daily life.
| Feature | Mounjaro (tirzepatide) | Saxenda (liraglutide) |
|---|---|---|
| Injection frequency | Once weekly | Once daily |
| Doses available | 2.5 mg, 5 mg, 7.5 mg, 10 mg, 12.5 mg, 15 mg | 0.6 mg → 3 mg (gradual escalation) |
| Injection sites | Abdomen, thigh, upper arm | Abdomen, thigh, upper arm |
| Pen type | Pre-filled autoinjector | Pre-filled dial-a-dose pen |
| Storage | Refrigerate; up to 30 days at room temperature | Refrigerate; up to 30 days at room temperature |
| Starting dose | 2.5 mg weekly (4 weeks) | 0.6 mg daily (week 1), escalating over 5 weeks |
For many patients, once-weekly dosing with Mounjaro represents a meaningful practical advantage over daily Saxenda injections — fewer administrations, less disruption to routine, and a lower total number of injections per year (52 vs 365). Both pens use a fine needle and are designed for self-administration.
Side Effects
Because both medications act on GLP-1 receptors, they share a closely related side-effect profile. The most common adverse effects are gastrointestinal and are typically most pronounced during the dose-escalation phase.
Common to both medications
- Nausea (most common; usually improves after the first 4–8 weeks at a stable dose)
- Diarrhoea
- Constipation
- Vomiting
- Reduced appetite (the intended therapeutic effect)
- Injection site reactions (redness, bruising, itching)
Seek urgent medical attention if you experience severe or persistent abdominal pain (possible pancreatitis), signs of an allergic reaction (facial swelling, difficulty breathing, widespread rash), or any rapidly developing serious symptom. Stop the injection and contact your GP or call 999.
In clinical trials, the overall tolerability profiles of tirzepatide and liraglutide were comparable. The once-weekly dosing of Mounjaro means that while the GI side-effect risk is similar, patients experience the injection itself less frequently.
Eligibility Criteria
The prescribing criteria for Mounjaro and Saxenda in the UK are effectively identical for weight management. Both are licensed for use alongside a calorie-reduced diet and increased physical activity.
- Adults aged 18 or over with a BMI of 30 kg/m² or above
- Or adults with a BMI of 27–29.9 kg/m² plus at least one weight-related comorbidity (such as type 2 diabetes, hypertension, or raised cholesterol)
- Committed to lifestyle modification alongside medication
Neither medication is suitable if you
- Are pregnant or breastfeeding
- Have a personal or family history of medullary thyroid carcinoma or Multiple Endocrine Neoplasia syndrome type 2 (MEN2)
- Have a history of pancreatitis
- Are already taking another GLP-1 receptor agonist, GIP agonist, or dual GIP/GLP-1 agonist
Mounjaro and Saxenda must never be taken simultaneously. Combining two GLP-1 or GIP/GLP-1 agonists carries significant risk and is not clinically appropriate.
Mounjaro vs Saxenda for Type 2 Diabetes
Both medications have beneficial effects on blood glucose and are used in patients who have obesity alongside type 2 diabetes. However, the licensed indications and relative efficacy differ in this population.
Tirzepatide holds a separate licence for the treatment of type 2 diabetes in adults (in addition to its weight management licence). Data from the SURPASS clinical programme demonstrate that tirzepatide produces superior reductions in HbA1c and greater body weight loss compared with liraglutide in people with type 2 diabetes. For patients managing both obesity and type 2 diabetes, tirzepatide is therefore likely to be the more clinically appropriate choice, subject to prescriber assessment.
Saxenda (liraglutide 3 mg) is licensed specifically for weight management and is distinct from Victoza (liraglutide 1.2–1.8 mg), which is the diabetes formulation. These products must not be used interchangeably. See our guide to what liraglutide is for further detail.
Switching from Saxenda to Mounjaro
Patients already established on Saxenda who wish to switch to Mounjaro can do so, but only under medical supervision. The following principles apply.
1
Consult your prescriber first
Do not stop Saxenda or start Mounjaro without speaking to a qualified prescriber. They will review your medical history, current medications, and weight loss progress.
2
Stop Saxenda
Saxenda must be discontinued before starting Mounjaro. Your prescriber will advise on the appropriate interval between stopping liraglutide and beginning tirzepatide.
3
Begin Mounjaro at the initiation dose
Regardless of the Saxenda dose you were taking, Mounjaro should be started at the 2.5 mg weekly initiation dose. Prior exposure to liraglutide does not justify skipping the escalation schedule.
4
Never take both simultaneously
Saxenda and Mounjaro must not be taken at the same time. Combining these medications is clinically contraindicated.
5
Update your prescriber on all medications
Inform your prescriber of every medication, supplement, and over-the-counter product you are taking to allow a safe and appropriate transition.
The Verdict: Which Is Right for You?
On pure efficacy data, Mounjaro demonstrates substantially greater average weight loss than Saxenda and is the stronger option for most patients seeking maximum effect from a weight management injection. Its once-weekly dosing also offers a practical advantage in daily life.
Mounjaro may be preferable if you
- Are seeking the highest level of evidence-supported weight loss
- Prefer once-weekly rather than daily injections
- Also have type 2 diabetes and require both glycaemic control and weight loss
- Have not previously responded adequately to GLP-1 monotherapy
Saxenda may still be appropriate if you
- Are already established on Saxenda and achieving satisfactory weight loss
- Have a specific contraindication to tirzepatide identified by your prescriber
- Your clinician recommends it based on your full medical history
- You prefer daily dosing for adherence or routine reasons
The right choice is made in the context of a full medical consultation. Neither medication is universally superior for every individual — clinical factors, medical history, and patient preference all inform prescribing decisions. Visit our weight loss treatment page to start a consultation with a GPhC-registered prescriber.
Prescription medication
Mounjaro (tirzepatide)
Dual GIP & GLP-1 receptor agonist. Once-weekly injection. Average 20.9% weight loss in clinical trials.
Start consultation →Prescription medication
Saxenda (liraglutide)
GLP-1 receptor agonist. Once-daily injection. Established safety record since 2017.
Read the Saxenda guide →Ready to start your weight loss consultation?
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Start Your ConsultationFrequently Asked Questions
Is Mounjaro better than Saxenda for weight loss?
In clinical trial data, Mounjaro (tirzepatide) produced substantially greater average weight loss than Saxenda (liraglutide) — approximately 20.9% versus 8% of body weight. However, these figures come from separate trials in different populations and cannot be treated as a direct head-to-head result. Individual outcomes vary, and the most appropriate medication depends on your full medical history and prescriber assessment.
Which is better for type 2 diabetes?
Mounjaro holds a separate licence for the treatment of type 2 diabetes and has demonstrated superior HbA1c reductions alongside greater weight loss in the SURPASS clinical programme. For patients managing both obesity and type 2 diabetes, tirzepatide is generally the more clinically appropriate option, though this remains subject to individual prescriber assessment.
Can I switch from Saxenda to Mounjaro?
Yes, switching is possible under medical supervision. Saxenda must be discontinued before starting Mounjaro. Regardless of the Saxenda dose you were taking, you should begin Mounjaro at the 2.5 mg initiation dose. Never take both medications simultaneously. Always consult your prescriber before making any change.
Which medication has fewer side effects?
Both medications share a similar gastrointestinal side-effect profile — nausea, diarrhoea, constipation, and vomiting are common to both, particularly during dose escalation. In clinical trials, overall tolerability was broadly comparable. The main practical difference is that Mounjaro is injected once weekly compared with Saxenda’s once-daily schedule.
Why might a prescriber choose Saxenda over Mounjaro?
A prescriber may recommend Saxenda if a patient has a specific contraindication to tirzepatide, is already established on Saxenda and achieving satisfactory results, has clinical reasons to prefer a GLP-1 monotherapy, or if the patient’s individual medical history and risk profile make liraglutide the more appropriate choice. Prescribing decisions account for many factors beyond headline trial data.
Is there a price difference between Mounjaro and Saxenda?
Pricing varies by pharmacy and dose. As a prescription-only medication obtained through a regulated pharmacy, both require a valid prescription. We recommend discussing costs directly with your prescriber or pharmacist. Access Doctor provides transparent pricing on the weight loss treatment page.
References
- Jastreboff AM, et al. Tirzepatide Once Weekly for the Treatment of Obesity. New England Journal of Medicine. 2022;387(3):205–216. (SURMOUNT-1)
- Pi-Sunyer X, et al. A Randomized, Controlled Trial of 3.0 mg of Liraglutide in Weight Management. New England Journal of Medicine. 2015;373(1):11–22. (SCALE Obesity)
- NICE Technology Appraisal TA1026. Tirzepatide for managing overweight and obesity. National Institute for Health and Care Excellence; 2024.
- NICE Technology Appraisal TA664. Liraglutide for managing overweight and obesity. National Institute for Health and Care Excellence; 2020.
- Frías JP, et al. Tirzepatide versus Semaglutide Once Weekly in Patients with Type 2 Diabetes. New England Journal of Medicine. 2021;385(6):503–515. (SURPASS-2)
Medical disclaimer: This article is for informational purposes only and does not constitute medical advice. Mounjaro and Saxenda are prescription-only medicines (POMs) and must only be used under the supervision of a qualified prescriber. Always consult a healthcare professional regarding your individual circumstances. Do not stop or start any prescription medication without medical guidance.