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
Will Wegovy Work If Mounjaro Didn't Work For You?
If Mounjaro hasn't delivered the weight loss results you hoped for, you may wonder whether Wegovy could be more effective. The short answer is: it's possible, but not assured. Both are prescription-only GLP-1-based medications licensed in the UK for weight management, but they work through different mechanisms and people respond differently to each. Your prescriber can assess whether switching makes sense based on your individual circumstances, side effects, and health profile.
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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 Differently
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist — it activates two hormone pathways simultaneously. This dual action may help regulate appetite, reduce cravings, and support feeling fuller after smaller meals. The SURMOUNT-1 trial showed average weight loss of around 15–21% of body weight depending on dose.
Wegovy (semaglutide) is a GLP-1 receptor agonist only — it activates a single hormone pathway. The STEP-1 trial showed average weight loss of approximately 14.9% of body weight at the maximum dose of 2.4mg. Both work alongside reduced-calorie diet and increased physical activity, and individual results vary significantly.
Because Mounjaro targets two pathways and Wegovy targets one, some people may respond better to one than the other — there's no way to predict this in advance without trying. If you had side effects on Mounjaro, Wegovy's single mechanism may cause different side effects, though many are similar between the two drugs.
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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.
Why Mounjaro Might Not Have Worked — and What's Next
Mounjaro may not deliver expected results for several reasons: dose may not have reached the therapeutic level needed (the standard titration starts at 2.5mg and increases weekly), you may have had side effects preventing adherence, or your body may simply respond better to a different mechanism. Some people also need longer to see results — weight loss typically accelerates over several weeks on the same dose.
If you're considering switching to Wegovy, your prescriber will want to know: how long you took Mounjaro, what dose you reached, whether you had side effects, and how consistent you were with the dose schedule. Use our GLP-1 weight loss calculator to understand what realistic expectations might be at different doses. Your GP or prescriber can then assess whether Wegovy is appropriate and plan the switch safely.
- 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.
Can I switch directly from Mounjaro to Wegovy?
Not directly — both are potent medications and switching requires careful prescriber oversight. You'll typically stop Mounjaro and wait at least a week before starting Wegovy at the lowest dose (0.25mg). Your prescriber will assess your suitability and manage the transition safely. Never switch without medical guidance.
Is Wegovy more effective than Mounjaro?
Clinical trials show similar average weight loss — Mounjaro around 15–21% and Wegovy around 14.9% — but individual responses vary. Some people respond better to Wegovy's single GLP-1 mechanism, others to Mounjaro's dual GIP+GLP-1 approach. Your prescriber can help decide based on your circumstances.
What if Wegovy doesn't work either?
If neither Mounjaro nor Wegovy delivers results, discuss alternative approaches with your prescriber: different dose protocols, combination with other treatments, bariatric surgery referral, or tier 3 NHS specialist services. Weight loss is complex — multiple factors affect response and multiple options exist.
How do Mounjaro and Wegovy doses compare?
Mounjaro doses (2.5–15mg weekly) are not directly equivalent to Wegovy doses (0.25–2.4mg weekly) — they're different molecules at different concentrations. Approximate equivalence: Mounjaro 5mg ≈ Wegovy 0.5mg, Mounjaro 10mg ≈ Wegovy 1.7mg, Mounjaro 15mg ≈ Wegovy 2.4mg — but your prescriber decides the appropriate Wegovy starting dose.
Will side effects be different on Wegovy if I had them on Mounjaro?
Possibly. Both share common side effects (nausea, diarrhoea, constipation) because both are GLP-1-based. But Mounjaro's dual mechanism may cause different symptoms in some people. Many find Wegovy's side effects more tolerable — this varies individually. Always report previous side effects to your prescriber.
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.