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
How Mounjaro Works For Weight Loss
Mounjaro (tirzepatide) is a prescription-only weekly weight loss injection that works differently to other GLP-1 medications like Wegovy. It's a dual GIP and GLP-1 receptor agonist, meaning it activates two natural hormone pathways in your body to help reduce appetite and support weight management. Understanding how Mounjaro works, and how it compares to alternatives, can help you have an informed conversation with your GP or prescriber about which prescription weight loss option might be suitable for you.
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.
Mounjaro's Dual Mechanism vs Wegovy's Single Action
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist — it activates two natural hormone pathways simultaneously. GIP (glucose-dependent insulinotropic polypeptide) and GLP-1 (glucagon-like peptide-1) are hormones your gut naturally produces after eating. By mimicking and amplifying these signals, Mounjaro may help reduce appetite, increase feelings of fullness, and slow how quickly food leaves your stomach.
Wegovy (semaglutide), by contrast, is a GLP-1-only receptor agonist — it activates the GLP-1 pathway but not GIP. This single-mechanism approach is also effective for weight loss, but the dual action of Mounjaro may explain some differences in clinical trial outcomes.
In the SURMOUNT-1 clinical trial, Mounjaro users lost an average of 15–21% of their body weight. In the STEP-1 trial, Wegovy users lost an average of 15% body weight. Both results were achieved alongside a reduced-calorie diet and increased physical activity — individual results vary significantly.
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.
Is One Better Than The Other?
Neither Mounjaro nor Wegovy is universally "better" — suitability depends on your individual health, medical history, and prescriber assessment. Both are prescription-only medications requiring a clinical assessment before a prescriber will decide if they're appropriate for you. Both are available through NHS specialist weight management services or private online prescribing in the UK.
Your prescriber will consider factors like any existing health conditions, other medications you're taking, and your personal weight loss goals. Some people may respond better to one medication than another, which is why individual variation is so important. Use our free GLP-1 weight loss calculator to explore potential outcomes, and discuss both options with your prescriber to find the right fit for your circumstances.
- 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's the difference between Mounjaro and Wegovy?
Mounjaro is a dual GIP+GLP-1 receptor agonist (two hormone pathways), while Wegovy is GLP-1-only. Both are prescription-only weekly injections for weight management. Clinical trials show Mounjaro users lost 15–21% body weight, Wegovy users 15% on average. Both require lifestyle changes and individual results vary.
How does Mounjaro help with weight loss?
Mounjaro activates GIP and GLP-1 hormone pathways, which signal fullness to your brain, reduce appetite, slow stomach emptying, and help regulate fat use. This dual action may help you feel satisfied with smaller portions and eat less overall, supporting a calorie deficit when combined with diet and exercise changes.
Is Mounjaro available on the NHS in the UK?
Yes, Mounjaro (tirzepatide) is approved by NICE for NHS specialist weight management services. Access varies by region and requires referral from your GP to tier 3 services. Waiting lists can be lengthy in some areas. Private prescription options are also available through UK-licensed online prescribers.
How long before Mounjaro starts working?
Initial effects (reduced appetite, nausea) can appear within days of the first dose. However, significant weight loss typically takes weeks to months. Clinical trials measured results over 72 weeks. Your prescriber will review progress regularly and adjust your dose every 4 weeks if needed to reach your maintenance dose.
Can you switch from Wegovy to Mounjaro?
Yes, switching between medications is possible, but it must be managed by your prescriber — never switch yourself. There is no official conversion chart, though approximate equivalences exist (Wegovy 2.4mg ≈ Mounjaro 10–15mg). Your prescriber will advise on the safest switching protocol based on your individual situation.
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.