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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5mg Mounjaro Pen vs Wegovy — Which Is Right for You?
Both Mounjaro (tirzepatide) and Wegovy (semaglutide) are prescription-only weight loss injections available in the UK, but they work differently and may suit different people. A 5mg Mounjaro pen represents an early dose in the titration schedule, equivalent to approximately 0.5mg Wegovy. This guide explains the key differences between these medications, how they compare clinically, and how to determine which might be suitable for you following a clinical assessment.
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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 Compare Clinically
Mechanism: Mounjaro is a dual GIP and GLP-1 receptor agonist, meaning it activates two separate hormone pathways. Wegovy is a GLP-1 receptor agonist only. This dual action in Mounjaro may contribute to its slightly higher average weight loss in clinical trials, though individual results vary significantly.
Clinical trial data: In the SURMOUNT-1 trial, Mounjaro at 15mg (maximum dose) achieved average weight loss of approximately 20.9% of body weight over 72 weeks. The STEP-1 trial showed Wegovy at 2.4mg (maximum dose) achieved approximately clinically studied weight loss over 68 weeks. However, both trials involved reduced-calorie diets and increased physical activity alongside medication. At the 5mg starting/adjustment dose, Mounjaro showed average weight loss of approximately 15% body weight in SURMOUNT trials.
- Mounjaro: once-weekly injection, dose range 2.5–15mg
- Wegovy: once-weekly injection, dose range 0.25–2.4mg
- Both require minimum 4-week periods at each dose before escalation
- Both are prescription-only and require clinical assessment
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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.
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Which Medication Is Right for You?
Neither Mounjaro nor Wegovy is universally "better" — suitability depends on your individual health profile, medical history, and how you respond to the medication. A UK-licensed prescriber will assess factors including your BMI, any weight-related health conditions, current medications, family history, and whether you've previously tried other weight management approaches. Use our free BMI calculator to establish your starting point, then discuss both options with your prescriber. Some people respond better to one mechanism than the other, and side effect tolerance varies significantly between individuals. Your prescriber may recommend trying one medication first, or may suggest one based on your specific circumstances. Both require lifestyle changes — diet and exercise — alongside medication for best results.
- 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 5mg Mounjaro equivalent to any Wegovy dose?
5mg Mounjaro is approximately equivalent to 0.5–1mg Wegovy in terms of effect, though there is no official conversion chart. The mechanisms differ (dual vs single action), so direct equivalence is not exact. Your prescriber can advise on switching between medications if needed.
Which injection causes fewer side effects — Mounjaro or Wegovy?
Both cause similar common side effects (nausea, diarrhoea, constipation, abdominal pain). Side effect frequency and severity vary between individuals. Some people tolerate one better than the other. Starting at a low dose (5mg Mounjaro or 0.25mg Wegovy) helps minimise side effects as the body adjusts.
Can I get either medication on the NHS?
Both Mounjaro and Wegovy are available through NHS specialist tier 3 weight management services, but availability varies by region and waiting lists can be very long. Private prescription via UK-licensed online prescribers is also available. Your GP can refer you to NHS services or you can access private assessment independently.
Which medication works faster for weight loss?
Both typically show measurable weight loss within 4–8 weeks of starting. Mounjaro's dual mechanism may provide slightly faster results on average according to clinical trials, but individual responses vary. The rate of weight loss depends more on adherence, diet, activity level, and how your body responds than which specific medication you use.
How long does a 5mg Mounjaro pen last?
Each Mounjaro KwikPen contains four once-weekly doses, so a single 5mg pen lasts approximately four weeks. You will typically progress to a higher dose after four weeks, so you would not remain on 5mg long-term unless that is determined as your maintenance dose by your prescriber. ```
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