The UK's most complete GLP-1 guide
Every Question Answered. Every Side Effect Explained.
- How GLP-1 medications work
- Mounjaro vs Wegovy compared
- Injection instructions
- Side effects & solutions
- What to eat on treatment
- FAQs answered
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1.25mg Mounjaro vs Wegovy — Detailed Comparison
If you're considering weight loss medication in the UK, you may have come across both Mounjaro (tirzepatide) and Wegovy (semaglutide). While 1.25mg isn't a standard Mounjaro dose, understanding how these two prescription-only injections compare helps you and your prescriber make an informed decision. Both are licensed for weight management in UK adults, but they work differently and have different dosing schedules. This guide compares the key differences factually, based on clinical trial data and NHS guidance.
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Enter your height and weight below. Supports both imperial (stone & lbs) and metric (kg). Results include NHS category, healthy weight range, and ethnicity adjustments.
What Is BMI and Why Does It Matter?
Body Mass Index (BMI) is the most widely used screening tool for assessing whether your weight falls within a healthy range. Used by the NHS, GPs, and weight management services across the UK, BMI provides a quick snapshot of your weight relative to your height. The formula is simple: your weight in kilograms divided by your height in metres squared (kg/m²).
While BMI isn't a perfect measure — it doesn't account for muscle mass, bone density, or fat distribution — it remains the standard first step in identifying potential weight-related health risks including type 2 diabetes, cardiovascular disease, high blood pressure, and certain cancers.
The NHS also recommends adjusted thresholds for people of South Asian, Chinese, or Black African heritage — a BMI of 23 or above is classified as overweight, and 27.5 as obese. Our calculator includes this adjustment as a one-click toggle.
How Mounjaro and Wegovy Work — Mechanism Comparison
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist, meaning it activates two natural hormone pathways simultaneously. This dual mechanism may support appetite regulation and help you feel fuller after smaller meals. It's administered as a once-weekly injection via a KwikPen device.
Wegovy (semaglutide) is a GLP-1 receptor agonist only, activating a single hormone pathway. While effective, it works through one mechanism rather than two. Wegovy is also a once-weekly injection but starts at a lower initial dose (0.25mg) compared to Mounjaro's starting dose (2.5mg).
- Mounjaro: dual mechanism — may offer additional appetite control
- Wegovy: single mechanism — well-established and extensively studied
- Both: once-weekly injections, prescription-only, require clinical assessment
Clinical trial data (SURMOUNT-1 for Mounjaro, STEP-1 for Wegovy) showed average weight loss of approximately 15–21% for Mounjaro and approximately 15% for Wegovy at maximum doses — though individual results vary significantly. Use our GLP-1 weight loss calculator to explore potential outcomes at different doses based on this trial data.
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How It Works
Three simple steps to understand your weight and take action.
Enter your height and weight in our free calculator. Get your BMI, NHS category, healthy weight range, and ethnicity-adjusted thresholds instantly.
If your BMI suggests you're overweight or obese, explore our GLP-1 calculators to project potential weight loss on Mounjaro or Wegovy.
Use our progress tracker to log your weight weekly, visualise your journey with charts, and stay motivated — all stored privately in your browser.
Free Weight Loss Tools & Guides
Everything you need to understand your weight, explore medication options, and track your progress — completely free.
Which is Right for You — Individual Suitability and Prescriber Choice
There is no universally "better" option — suitability depends on your individual health profile, medical history, and how your body responds to treatment. Your GP or prescriber will assess factors including your BMI, any weight-related health conditions (such as type 2 diabetes or hypertension), medication interactions, and contraindications. Both medications require a prescription and clinical assessment before being dispensed.
Key suitability factors:
- Oral contraceptive use — Mounjaro may reduce absorption; Wegovy has no specific interaction
- Gallbladder history — both require careful consideration
- Gastroparesis — contraindicated for both
- Preference for single vs dual mechanism — personal choice with prescriber guidance
Check your BMI using our free BMI calculator as a starting point for discussion with your prescriber about weight loss medication eligibility.
- Dual GIP/GLP-1 receptor agonist
- Up to 22.5% body weight loss (SURMOUNT-1)
- Weekly injection, dose escalation over 20+ weeks
- Available via private prescription in the UK
- Doses: 2.5mg → 5mg → 7.5mg → 10mg → 12.5mg → 15mg
- GLP-1 receptor agonist
- Up to 15–17% body weight loss (STEP trials)
- Weekly injection, 5-step dose escalation
- NHS & private prescription available
- Doses: 0.25mg → 0.5mg → 1mg → 1.7mg → 2.4mg
Mounjaro vs Wegovy: Head-to-Head
A side-by-side comparison of the two most popular GLP-1 weight loss medications available in the UK.
| Feature | Mounjaro | Wegovy |
|---|---|---|
| Drug class | Dual GIP/GLP-1 agonist | GLP-1 agonist |
| Active ingredient | Tirzepatide | Semaglutide |
| Avg. weight loss | 15–22.5% | 12–17% |
| Key trial | SURMOUNT-1 (2022) | STEP 1 (2021) |
| Max dose | 15 mg weekly | 2.4 mg weekly |
| Escalation period | 20–32 weeks | 16–20 weeks |
| Administration | Weekly injection (pen) | Weekly injection (pen) |
| NHS availability | Private prescription only | NHS & private |
| Approx. private cost | £150–£250/month | £150–£300/month |
| Common side effects | Nausea, diarrhoea, constipation | Nausea, vomiting, diarrhoea |
Data sourced from SURMOUNT-1 and STEP 1 clinical trials. Costs are approximate and vary by provider. Always consult a prescriber.
Am I Eligible for Weight Loss Medication?
In the UK, eligibility for GLP-1 weight loss medications like Mounjaro and Wegovy is based on your BMI and overall health profile.
- BMI of 30 or above (obese)
- Age 18 or over
- No contraindicated conditions
- Committed to lifestyle changes
- BMI of 27 or above
- Plus type 2 diabetes
- Or high blood pressure
- Or obstructive sleep apnoea
Use our BMI calculator to check whether your BMI falls within the eligible range.
How We Built These Tools
Every calculator and guide on myweightcheck is built with accuracy and transparency in mind. Our BMI calculator uses the standard WHO formula with NHS-aligned category thresholds. Our GLP-1 projections are modelled on published clinical trial data from SURMOUNT and STEP studies.
All data stays on your device. We don't require sign-ups, and we don't store your health information on any server. Your progress tracker saves data locally in your browser using localStorage, so only you can see it.
We're based in the UK and our tools are designed specifically for UK users — supporting stone & lbs by default, referencing NHS guidelines, using NICE-approved medication data, and linking to GPhC-registered pharmacies.
Frequently Asked Questions
Common questions about BMI, weight loss medications, and our free UK tools.
Is Mounjaro stronger than Wegovy?
"Stronger" isn't the right term. Mounjaro has a dual mechanism (GIP+GLP-1) while Wegovy has a single mechanism (GLP-1 only). Clinical trials showed similar average weight loss at maximum doses, but individual responses vary. Prescriber choice depends on your personal health profile, not inherent superiority of either medication.
What's the difference in starting doses?
Mounjaro starts at 2.5mg once weekly. Wegovy starts at 0.25mg once weekly — a much lower initial dose. Mounjaro typically escalates faster. Both reach maximum doses after several weeks of titration guided by your prescriber.
Can I switch from Mounjaro to Wegovy mid-treatment?
Switching between medications should only be done under prescriber guidance. There is no official established conversion chart between doses — your prescriber will manage any transition carefully and monitor your response.
Does NHS prescribe both Mounjaro and Wegovy?
NICE has approved tirzepatide (Mounjaro) within NHS specialist weight management services. Availability varies significantly by region and waiting lists can be lengthy. Wegovy is also available through NHS specialist services in some areas. Private prescribing is available for both through UK-licensed prescribers.
Which has fewer side effects?
Both share similar side effects — nausea, diarrhoea, constipation, and stomach pain are common early on. Tolerability varies individually. Neither medication is proven to have fewer side effects than the other. Your prescriber will discuss expected side effects and management strategies during your clinical assessment.
Ready to take control of your weight loss journey?
Start with a free BMI check, explore your GLP-1 options, or begin tracking your progress today. No sign-up. No cost. Just results.