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
Mounjaro vs Wegovy — Complete UK Comparison
Mounjaro and Wegovy are both prescription-only weight loss injections available in the UK, but they work differently. Mounjaro uses a dual GIP and GLP-1 mechanism, while Wegovy is a GLP-1 agonist only. Both are licensed for weight management in UK adults and require a clinical assessment before prescription. This guide compares the two directly so you can understand the key differences — though your prescriber will ultimately advise which is most suitable for your individual health needs.
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) activates two hormone pathways: GIP (glucose-dependent insulinotropic polypeptide) and GLP-1. This dual mechanism may help regulate appetite more effectively by signalling fullness through two different biological routes. The tirzepatide formulation is delivered via a KwikPen once weekly, starting at 2.5 mg and escalating up to 15 mg.
Wegovy (semaglutide) works through the GLP-1 pathway alone, reducing appetite and slowing gastric emptying. It is also injected once weekly, starting at 0.25 mg and escalating to a maximum dose of 2.4 mg. Both medications slow how quickly food leaves your stomach and signal satiety to the brain, though Mounjaro's dual action may offer a different biological effect.
Clinical trial data from SURMOUNT (Mounjaro) and STEP (Wegovy) showed different average weight loss outcomes, though individual results vary significantly based on lifestyle, genetics, and adherence to reduced-calorie diet and physical activity.
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.
Clinical Trial Results and Eligibility in the UK
In the SURMOUNT-1 trial, Mounjaro at 15 mg resulted in approximately 20.9% average body weight loss over 72 weeks. The STEP-1 trial showed Wegovy at 2.4 mg achieved approximately 14.9% average weight loss over 68 weeks. Both trials included participants following a reduced-calorie diet and increased physical activity — medication alone does not clinically studied weight loss.
Both medications are prescribed to UK adults with a BMI of 30 or above, or BMI 27–29.9 with weight-related health conditions such as type 2 diabetes, high blood pressure, or cardiovascular disease. Access is through NHS specialist weight management services or private online prescribing following clinical assessment. Your GP or prescriber will determine which medication suits your individual circumstances — factors like your medical history, other medications, and previous treatment responses all inform this decision.
Track your weight loss journey and monitor your progress using our free progress tracker, which works alongside whichever medication your prescriber recommends. You can also use our GLP-1 weight loss calculator to explore potential outcomes at different doses, though remember that individual results vary and depend on lifestyle factors as well as the medication itself.
- 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.
What is the main difference between Mounjaro and Wegovy?
Mounjaro is a dual GIP and GLP-1 agonist, while Wegovy is GLP-1 only. This means Mounjaro activates two appetite-regulating pathways, whereas Wegovy activates one. Both are once-weekly injections approved for UK weight management, but the different mechanisms may suit different individuals.
Which medication causes more weight loss, Mounjaro or Wegovy?
Clinical trials show Mounjaro at 15 mg achieved approximately 20.9% average weight loss, while Wegovy at 2.4 mg achieved approximately 14.9% average weight loss. However, individual results vary significantly. Neither medication assures specific weight loss — both work best alongside a reduced-calorie diet and increased physical activity. Your prescriber will advise which is suitable for you.
Can I switch from Wegovy to Mounjaro or vice versa?
Yes, it is possible to switch between the two medications, but this must be managed by your prescriber. There is no official established conversion chart between the doses, so switching requires a clinical assessment. Any change in medication should only happen under professional guidance.
How do I access Mounjaro or Wegovy on the NHS in the UK?
Both medications are available through NHS specialist tier 3 weight management services, typically accessed via GP referral. However, NHS availability and waiting times vary significantly by region. Alternatively, both are available through private online prescribing following a clinical assessment with a UK-licensed prescriber.
What are the common side effects of both medications?
Both commonly cause nausea, diarrhoea, vomiting, and constipation — typically mild and improving over time. Both also list injection site reactions, fatigue, and dizziness. Serious side effects are rare but can include severe stomach pain. Always read the patient information leaflet and discuss side effects with your prescriber before starting.
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.