Choosing between Mounjaro and Wegovy can feel overwhelming. Both are once-weekly prescription weight loss injections that work by targeting appetite and metabolic hormones, and both have demonstrated significant results in large clinical trials.

However, there are important differences in:

• Mechanism of action
• Expected weight loss
• Dosing schedules
• Cardiovascular licensing
• Device design
• Cost
• Suitability for different patient profiles

This guide provides a strict, evidence-based comparison to help you understand which option may be most appropriate for your circumstances. Individual suitability must always be confirmed through a clinical assessment.

Key Differences at a Glance

• Mounjaro activates two hormone pathways (GIP and GLP-1); Wegovy activates GLP-1 only.
• Mounjaro demonstrates dose-dependent mean weight loss of approximately 15–21% at 72 weeks in clinical trials.
• Wegovy demonstrates mean weight loss of 14.9% at 68 weeks (STEP 1 trial).
• Wegovy is licensed for cardiovascular risk reduction in certain eligible patients; Mounjaro is not currently licensed for this indication.
• Wegovy starts from £89.99; Mounjaro starts from £139.99.

How Do Mounjaro and Wegovy Work?

Both medications are incretin-based therapies. They mimic hormones involved in appetite regulation, insulin response and gastric emptying, making it easier to sustain a calorie deficit when combined with dietary and lifestyle changes. Our expert Mounjaro diet plan guide explains how to structure meals, manage appetite changes and choose foods that support healthy weight loss during treatment.

How Wegovy Works (Semaglutide)

Wegovy contains semaglutide, a GLP-1 receptor agonist. GLP-1 signalling:

• Signals fullness to the brain
• Slows gastric emptying
• Reduces appetite
• Improves insulin secretion

By strengthening these signals, Wegovy helps reduce calorie intake and supports sustained weight loss alongside lifestyle changes.

How Mounjaro Works (Tirzepatide)

Mounjaro contains tirzepatide, a dual GIP and GLP-1 receptor agonist. It activates:

• GLP-1 (as above)
• GIP (glucose-dependent insulinotropic polypeptide)

GIP activity may:

• Enhance insulin release after meals
• Improve metabolic regulation
• Support fat metabolism
• Work synergistically with GLP-1

This dual mechanism is one proposed reason for the higher average weight loss observed in tirzepatide trials.

Clinical Evidence: What Do the Studies Show?

Wegovy – STEP Trials

In the STEP 1 trial (68 weeks):

• Mean weight loss: 14.9%
• Up to 86% of participants achieved at least 5% weight loss.

Mounjaro – SURMOUNT-1 Trial

In the SURMOUNT-1 trial (72 weeks):

• Mean weight loss ranged from approximately 15% to 21%, depending on dose (5mg–15mg).
• Up to 96% of participants at higher doses achieved at least 5% weight loss.

Direct Head-to-Head Comparison

A direct comparison study published in the New England Journal of Medicine reported:

• Mounjaro: approximately 20% mean weight loss
• Wegovy: approximately 14% mean weight loss
• 32% of Mounjaro users lost ≥25% body weight
• 16% of Wegovy users lost ≥25% body weight

The study was funded by Eli Lilly, manufacturer of Mounjaro. Individual outcomes still vary based on dose, adherence and lifestyle factors.

Licensing & Approved Uses (UK)

Wegovy

• Licensed for chronic weight management in eligible adults (SELECT Trial)
• Licensed for cardiovascular risk reduction in certain patients with established cardiovascular disease (where clinically appropriate).

Mounjaro

• Licensed for chronic weight management in eligible adults.
• Also used for glycaemic management indications depending on labelling and clinical context.
• Not currently licensed specifically for cardiovascular risk reduction.

Why this matters: For patients with established cardiovascular disease, licensed cardiovascular risk reduction may be a deciding factor to discuss during prescribing review.

Titration (Dose Escalation)

Both treatments use a gradual dose-increase plan to help your body adapt and to reduce gastrointestinal side effects. This step-up approach is called titration. Your prescriber may slow down dose increases if side effects are difficult or if you are achieving good results at a lower dose.

Your maintenance dose is the dose you remain on longer term because it provides the most consistent appetite and weight-management effect for you.

Wegovy titration schedule: 0.25mg → 0.5mg → 1mg → 1.7mg → 2.4mg

Mounjaro titration schedule: 2.5mg → 5mg → 7.5mg → 10mg → 12.5mg → 15mg

Dosing and Titration Schedules (Typical)

Wegovy Dosing Schedule

• Weeks 1–4: 0.25mg
• Weeks 5–8: 0.5mg
• Weeks 9–12: 1.0mg
• Weeks 13–16: 1.7mg
• Week 17 onward: 2.4mg (maintenance)

Mounjaro Dosing Schedule

• Weeks 1–4: 2.5mg (starter dose)
• Weeks 5–8: 5mg
• Weeks 9–12: 7.5mg
• Weeks 13–16: 10mg
• Weeks 17–20: 12.5mg
• Week 21 onward: 15mg (maximum)

Important: The 2.5mg starter dose is primarily intended for tolerability and dose initiation rather than maximum weight-loss effect. Read more in our Mounjaro dosing schedule guide.

Wegovy vs Mounjaro Cost Comparison

Pen & Device Differences

Practical usability matters. Both treatments are once-weekly subcutaneous injections and require safe sharps disposal, but device handling can differ.

Mounjaro

• Single-use, pre-filled pen for weekly dosing (one injection per pen).
• Designed to minimise steps for the injection process.

Wegovy

• Pre-filled pen device for weekly dosing.
• Administration steps can vary slightly depending on the pen format supplied.

Storage basics: Both are typically stored refrigerated before first use. Always follow the patient information leaflet for storage limits and disposal guidance.

Side Effects: Side-by-Side Comparison

Both medications share similar gastrointestinal side effects because they affect appetite signalling and gastric emptying. The likelihood and severity can vary by dose, titration pace, and individual sensitivity.

Side Effects: Shared vs Medication-Specific

Side effects can vary by individual, dose, and titration speed. The table below separates shared effects from effects presented as more medication-specific in comparison-style summaries.

How to Manage Side Effects (Practical Guidance)

• Eat smaller meals and avoid very rich foods, especially during titration.
• If nausea is worse after eating, reduce high-fat meals and eat more bland foods temporarily.
• Stay hydrated; consider oral rehydration/electrolytes if vomiting or diarrhoea persists.
• Avoid overeating once appetite reduces (this can worsen nausea).
• If side effects are difficult, your prescriber may slow titration or delay dose increases.

Seek urgent medical advice for severe abdominal pain, signs of allergic reaction, or persistent vomiting/diarrhoea causing dehydration.

For a full breakdown of side-effect frequency, severity patterns and practical management strategies specific to tirzepatide, see our guide to Mounjaro side effects and how to treat them.

Is Mounjaro Better Than Wegovy?

Neither treatment is universally “better”. The best option depends on your medical history, how you tolerate each medication, and what outcomes matter most to you.

Choice may be influenced by:

• Tolerability: some people experience more side effects on one treatment than the other.
• Response: individuals can respond differently even within the same drug class.
• Medical context: cardiovascular licensing may matter for some patients; diabetes status may matter for others.
• Practical factors: device preferences, availability and cost.
• Interactions: your current medications and risk factors.

If side effects are unmanageable or results are not as expected, a clinician may consider dose-pacing adjustments or switching — but this should always be supervised.

Which Treatment May Be More Suitable?

Mounjaro May Be Considered If:

• Greater overall weight reduction is required
• You have type 2 diabetes (where clinically appropriate)
• Previous GLP-1 therapy was insufficient
• Higher BMI requires a more intensive escalation approach

Wegovy May Be Considered If:

• You have established cardiovascular disease and cardiovascular risk reduction is relevant
• You want a GLP-1 option with a longer history in weight management
• Cost sensitivity is an important factor

Oral contraception note (important)

Mounjaro can affect the absorption of oral contraceptives during dose escalation due to delayed gastric emptying. If you rely on the pill, discuss additional contraception (e.g. barrier methods) with your prescriber during titration.

Suitability must always be determined through a clinical assessment.

Switching Between Mounjaro and Wegovy

Yes — switching is possible, provided your prescriber confirms it is safe and appropriate for you.

Key switching principles:

• Do not overlap treatments.
• Allow a washout period so the first medication is sufficiently cleared (often around 5 weeks after Wegovy before starting Mounjaro).
• Restart at the lowest initiation dose and re-titrate.
• Monitor side effects closely during the switch.

If you are specifically moving from tirzepatide to semaglutide, read our step-by-step guide on how to switch from Mounjaro to Wegovy safely, including washout timing and dose re-initiation.

Why Would You Switch?

• Results: you’re not seeing the progress you expected despite adherence.
• Tolerability: side effects are persistent or disruptive.
• Preference: you prefer the dosing structure, device, availability or cost of another option.

You do not need to make this decision alone — your prescribing team can guide you to the safest, most appropriate choice.

What to Expect: Treatment Timeline

Weeks 1–4

• Appetite changes begin
• Starter dose phase
• Possible mild gastrointestinal effects

Months 2–4

• Steady weight reduction
• Dose escalation phase

Months 6–12+

• Maintenance phase
• Possible plateaus
• Focus shifts to sustainability

If you’re considering tirzepatide specifically, our detailed guide on Mounjaro weight loss timeline and expected results explains typical monthly progress, plateau phases and what influences outcomes.

Cost and NHS Availability

NHS access is currently limited and often restricted to specialist Tier 3 weight management services, with waiting times varying by region.

Private treatment through regulated pharmacies can offer:

• Online consultation
• Prescription review
• Ongoing monitoring
• Home delivery

NICE has issued guidance for semaglutide in weight management (TA875)

Tirzepatide has been assessed under NICE guidance (TA1026)

Long-Term Use and Stopping Treatment

Weight regain can occur if medication is stopped without a long-term plan.If you are considering discontinuing tirzepatide, our guide on what happens when you stop taking Mounjaro explains appetite rebound, metabolic changes and strategies to reduce regain.

 Sustainable results are most likely when treatment is combined with:

• Behavioural strategies
• Nutritional planning
• Physical activity
• Ongoing clinical review

Eligibility Criteria

You may qualify if:

• BMI 30+, or
• BMI 27+ with a weight-related condition such as:
  • Type 2 diabetes
  • High blood pressure
  • High cholesterol
  • Sleep apnoea

You can check your BMI instantly using our online BMI and weight loss eligibility calculator before starting your consultation.