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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Wegovy 1mg vs Mounjaro — Which Is Right for You?
Both Wegovy and Mounjaro are prescription-only weight loss injections available in the UK, but they work differently. Wegovy contains semaglutide (a GLP-1 receptor agonist), while Mounjaro contains tirzepatide (a dual GIP and GLP-1 agonist). Understanding the differences between them — including mechanism, dosing, clinical trial data, and eligibility — can help you and your GP make an informed decision about which may be suitable for your circumstances. Neither medication is assured to work, and individual results vary significantly.
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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 1mg and Mounjaro Work Differently
Wegovy (semaglutide) activates only the GLP-1 receptor pathway. At 1mg, you're in the mid-range of Wegovy's titration schedule (0.25mg to 2.4mg maximum). GLP-1 agonists work by signalling to your brain that you're full, reducing appetite, and slowing how quickly food leaves your stomach.
Mounjaro (tirzepatide) is a dual agonist, activating both GIP (glucose-dependent insulinotropic polypeptide) and GLP-1 pathways simultaneously. This dual mechanism may provide additional appetite suppression compared to GLP-1 alone. Mounjaro's equivalent dose range is 2.5mg to 15mg weekly.
Clinical trial context: SURMOUNT-1 data showed Wegovy achieved average weight loss of around 14.9% body weight at 68 weeks on the maximum 2.4mg dose. SURMOUNT trials for tirzepatide showed approximately 15–21% average weight loss depending on dose. Both studies involved participants following reduced-calorie diets and increased physical activity — medication alone does not produce these results.
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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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Dosing, Side Effects, and Individual Suitability
Wegovy at 1mg typically sits around weeks 9–12 of the titration schedule; you'd continue escalating toward the 2.4mg maintenance dose if tolerated. Mounjaro requires a slower titration starting at 2.5mg, with increments every 4 weeks, potentially reaching 15mg maximum.
Both medications commonly cause nausea, diarrhoea, constipation, and stomach discomfort — particularly during dose increases. Side effect profiles are similar, though individual tolerance varies.
Prescriber decision: Your GP or licensed prescriber will assess your medical history, current medications (especially contraceptive pills, which may have reduced absorption with GLP-1 medication), and overall health to determine which is more appropriate for you. Eligibility requires a BMI of 30 or above, or 27–29.9 with weight-related health conditions. Use our GLP-1 weight loss calculator to explore potential outcomes, and our BMI calculator to confirm your starting point.
- 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 stronger than Wegovy 1mg?
Mounjaro and Wegovy work through different mechanisms — Mounjaro's dual GIP+GLP-1 action differs from Wegovy's single GLP-1 pathway. Clinical trials suggest Mounjaro may produce slightly higher average weight loss, but results vary dramatically between individuals. "Stronger" isn't accurate; "different mechanism" is more precise. Your prescriber decides which suits you.
What's the Mounjaro equivalent of Wegovy 1mg?
Approximate equivalence suggests Wegovy 1mg is roughly comparable to Mounjaro 5–7.5mg, though there's no official conversion chart. Dosing is individualised — any switch between medications must be managed by your prescriber, not self-directed.
Can I switch from Wegovy to Mounjaro?
Yes, switching is possible and sometimes done in clinical practice, but it requires prescriber guidance. You cannot simply swap doses — your prescriber will assess your response to Wegovy and may recommend a specific Mounjaro starting dose based on your individual situation and tolerability.
Which has fewer side effects — Wegovy or Mounjaro?
Both medications share similar common side effects: nausea, diarrhoea, constipation, and stomach pain. Individual tolerability varies widely. Some people tolerate one better than the other, but clinical data doesn't show one as systematically "gentler." Your GP can discuss side effect management strategies.
How do I access Wegovy or Mounjaro in the UK?
Both are prescription-only and available through NHS specialist tier 3 weight management services (with significant regional variation and waiting lists) or through private online consultations with UK-licensed prescribers. You'll need a clinical assessment confirming eligibility — BMI 30+ or 27+ with weight-related conditions — before either can be prescribed.
Ready to take control of your weight loss journey?
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