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
Free tracker included with every download this week
5ml Mounjaro vs Wegovy — What's the Difference?
Both Mounjaro and Wegovy are prescription-only weight management injections available in the UK, but they work differently and use different dosing schedules. A 5ml Mounjaro pen contains multiple doses (not a single 5ml vial), whereas Wegovy is titrated from lower doses. Understanding how these medications compare—their mechanisms, trial results, and suitability—helps you and your prescriber make an informed decision. Both require clinical assessment and work best alongside dietary changes and increased physical activity.
10,000+ calculations today · NHS-aligned thresholds · 100% free
Calculate Your BMI Instantly
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 Differently
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist. This means it activates two natural hormone pathways simultaneously—GIP (glucose-dependent insulinotropic polypeptide) and GLP-1 (glucagon-like peptide-1)—which may enhance appetite regulation and support feeling fuller after meals.
Wegovy (semaglutide) is a GLP-1 receptor agonist only, activating just the GLP-1 pathway. Both medications slow gastric emptying, but Mounjaro's dual mechanism may offer a different effect profile.
In clinical trials, this dual action was associated with slightly greater average weight loss for Mounjaro, though individual results vary significantly. Your prescriber will assess which mechanism suits your health profile and medical history best. Use our GLP-1 weight loss calculator to explore projected weight loss ranges with either medication.
Clinically BackedWeight Loss
No appointments. No waiting rooms. Just care — from a UK-regulated online pharmacy.
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.
Dosing Schedules and Clinical Trial Results
Mounjaro dosing: Starts at 2.5mg weekly, escalating every 4 weeks to a maximum of 15mg weekly. A 5ml KwikPen contains 4 weekly doses. SURMOUNT-1 trial data showed average weight loss of approximately 15% (at 5mg), 19.5% (at 10mg), and 20.9% (at 15mg) over 72 weeks.
Wegovy dosing: Starts at 0.25mg weekly, escalating through 0.5mg, 1mg, 1.7mg to a maximum of 2.4mg. STEP-1 trial data showed average weight loss of approximately 14.9% at 68 weeks on the maximum dose.
Both are once-weekly injections. Approximate dose equivalence exists (5mg Mounjaro ≈ 0.5mg Wegovy), but these are clinical guidance only—your prescriber decides your specific regimen. Track your progress using our free progress tracker once you begin treatment.
- 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 5ml Mounjaro a single dose or multiple doses?
A 5ml Mounjaro KwikPen contains 4 weekly doses. Each pen supplies a month's worth of injections. Doses range from 2.5mg to 15mg depending on your treatment plan. Your prescriber will specify which dose you receive in each KwikPen.
Which works better for weight loss—Mounjaro or Wegovy?
Clinical trials show both support weight loss, with Mounjaro averaging slightly higher percentages in trials. However, "better" depends on your individual health, medical history, and how your body responds. Results vary significantly between people. Your GP or prescriber will assess which suits you best.
Can I switch from Wegovy to Mounjaro or vice versa?
Switching between medications is possible but must be managed by your prescriber. There is no official NHS conversion chart—approximate equivalences exist, but any switch requires medical oversight. Do not change medications without consulting your healthcare provider.
How much does 5ml Mounjaro cost in the UK?
Private costs vary by prescriber and dose, typically £129–£320 per month. NHS access is through specialist tier 3 weight management services where available, though waiting lists vary significantly by region. Your GP can advise on local NHS options.
Do Mounjaro and Wegovy have the same side effects?
Both commonly cause nausea, diarrhoea, vomiting, and constipation, especially at the start. Side effect profiles are similar because both are GLP-1 agonists. However, individual experiences vary. Your prescriber will discuss potential side effects and how to manage them during treatment.
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.