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
What Is The Difference Between Wegovy And Mounjaro?
Both Wegovy and Mounjaro are prescription-only weight loss injections available in the UK, but they work in different ways and have different dosing schedules. Wegovy contains semaglutide and activates one hormone pathway (GLP-1), whilst Mounjaro contains tirzepatide and activates two pathways (GIP and GLP-1). Understanding these differences helps you and your GP discuss which medication might be more suitable for your individual circumstances. This guide breaks down the key distinctions between these two weight management options.
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 Wegovy And Mounjaro Work Differently
Wegovy (semaglutide) is a GLP-1 receptor agonist, meaning it activates the GLP-1 hormone pathway. This single mechanism helps reduce appetite, increase feelings of fullness, and slow how quickly food leaves your stomach. In clinical trials (STEP-1), Wegovy helped participants lose an average of approximately 14.9% of their body weight over 68 weeks.
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist. By activating both the GIP and GLP-1 pathways simultaneously, Mounjaro may offer enhanced appetite suppression and metabolic effects. In the SURMOUNT-1 trial, Mounjaro helped participants lose an average of 15% to 21% of their body weight, depending on the dose used. The dual mechanism is what makes Mounjaro's pharmacology distinct from single-pathway GLP-1 medications like Wegovy.
- Wegovy: single GLP-1 mechanism
- Mounjaro: dual GIP + GLP-1 mechanism
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 Starting Doses
Both medications are once-weekly injections, but their dose ranges differ. Wegovy starts at 0.25 mg and escalates to a maximum of 2.4 mg over approximately 16 weeks. Mounjaro starts at 2.5 mg and can escalate up to 15 mg over several months. Because of these different dose ranges, approximate equivalences exist—for example, 2.4 mg Wegovy roughly corresponds to 15 mg Mounjaro—but any switch between medications must be managed by your prescriber and cannot be done directly. Both require a prescription from a UK-licensed healthcare professional following a clinical assessment of your eligibility and health status.
Our free GLP-1 weight loss calculator can help you explore potential outcomes at different dose levels for either medication.
- 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 more effective than Wegovy?
Clinical trial data suggests Mounjaro may produce slightly higher average weight loss (15–21%) compared to Wegovy (approximately 15%), but individual results vary significantly. The "best" option depends on your personal health profile, medical history, and how your body responds. Your prescriber will assess which is more suitable for you.
Can I switch from Wegovy to Mounjaro or vice versa?
Switching between these medications must only be done under prescriber guidance—it is not a straightforward switch due to different dose ranges and mechanisms. Your GP or specialist weight management service will manage any transition safely, including appropriate dose adjustments and monitoring.
Which has fewer side effects, Wegovy or Mounjaro?
Both medications share similar common side effects including nausea, diarrhoea, and stomach discomfort. The frequency and severity vary between individuals. Neither medication is inherently "safer"—side effects depend on your personal tolerance, dose, and health factors. Your prescriber will discuss this during assessment.
How do I access Wegovy or Mounjaro on the NHS in the UK?
Both medications are available through NHS specialist weight management services (tier 3), but access varies significantly by region and NHS Integrated Care Board. Your GP can refer you to your local specialist service. Private prescription access is also available through UK-licensed online prescribers following a clinical assessment.
Is Mounjaro the same as Ozempic?
No. Mounjaro and Ozempic both come from Eli Lilly and Novo Nordisk respectively, but Mounjaro contains tirzepatide (dual mechanism) whilst Ozempic contains semaglutide at lower doses. Ozempic is licensed for type 2 diabetes, not weight loss. Wegovy is the UK-licensed weight management version of semaglutide. Always use the correct licensed medication for the intended purpose.
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.