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 Does Mounjaro Make You Lose Weight?
Mounjaro (tirzepatide) is a prescription-only weekly weight loss injection that works by activating two natural hormone pathways to help reduce appetite and support weight management. Unlike other weight loss medications available in the UK, Mounjaro uses a dual GIP and GLP-1 receptor agonist mechanism, which means it targets two different hormonal signals that regulate hunger and satiety. In clinical trials, Mounjaro helped people lose an average of 15–21% of their body weight when combined with a reduced-calorie diet and increased physical activity, though individual results vary significantly. Understanding how it works can help you discuss this prescription weight loss option with your GP or a licensed prescriber.
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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.
Mounjaro's Dual Mechanism vs Wegovy
Mounjaro works through a dual mechanism that sets it apart from other weekly weight loss injections available in the UK. It activates both GIP (glucose-dependent insulinotropic polypeptide) and GLP-1 (glucagon-like peptide-1) receptors—natural hormone pathways that control appetite and food intake.
- GLP-1 activation signals to your brain that you feel full after eating less food, reducing hunger and cravings
- GIP activation enhances the effect further by regulating how your body processes nutrients and uses fat for energy
- Gastric emptying is slowed, meaning food stays in your stomach longer, promoting prolonged satiety
In comparison, Wegovy (semaglutide) uses GLP-1 activation alone. Clinical trial data from SURMOUNT-1 showed Mounjaro achieved average weight loss of approximately 15% at 5mg dose, 19.5% at 10mg, and 20.9% at the maximum 15mg dose over 72 weeks. Wegovy's STEP trials showed approximately 14.9% average weight loss at its maximum 2.4mg dose. Both results were achieved alongside dietary and lifestyle modifications—medication alone is not the answer.
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.
Individual Suitability and NHS Access
Whether Mounjaro or Wegovy is more suitable depends entirely on your individual health circumstances, which is why prescription and clinical assessment are essential. Your GP or a licensed prescriber will consider your BMI, weight-related health conditions, medical history, and other medications before deciding which option—if any—is appropriate for you.
In the UK, both medications are available through NHS specialist tier 3 weight management services (though access varies significantly by region and waiting lists can be lengthy) or through private prescribing following an online clinical assessment. Use our free GLP-1 weight loss calculator to explore potential outcomes at different doses, and our BMI calculator to understand your current weight category according to NHS guidelines. Your prescriber will determine the best starting dose and titration schedule tailored to your needs.
- 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.
Does Mounjaro burn fat or just reduce appetite?
Mounjaro works primarily by reducing appetite and helping you feel fuller faster, which creates a calorie deficit. The dual GIP/GLP-1 mechanism also supports improved fat utilisation and metabolism. Weight loss comes from consuming fewer calories than you burn, not from the medication "burning" fat directly. Combined with reduced-calorie diet and physical activity, this creates sustainable weight loss.
How quickly will I lose weight on Mounjaro?
Clinical trials show variable results—some people see weight loss within weeks, others take longer. Average weight loss in SURMOUNT trials was 15–21% over 72 weeks, but individual responses vary based on genetics, diet adherence, activity level, and starting weight. Your prescriber will monitor your progress and adjust doses accordingly.
Is Mounjaro better than Wegovy for weight loss?
Clinical trial data suggests Mounjaro may produce slightly higher average weight loss (20.9% at maximum dose) versus Wegovy (14.9% at maximum dose), but differences are modest and individual results vary widely. The "better" option depends on your personal health profile, which your prescriber will assess. Both are prescription-only and require clinical evaluation.
How does Mounjaro compare to diet and exercise alone?
Mounjaro is not a substitute for diet and exercise—it's a tool to support them. Studies show that Mounjaro works best when combined with a reduced-calorie diet and increased physical activity. The medication helps reduce hunger signals, making it easier to stick to healthy habits, but behaviour change remains essential for sustained results.
Can I get Mounjaro on the NHS in the UK?
Yes, Mounjaro is NICE-approved for NHS use, but access is through specialist tier 3 weight management services, not standard GP prescriptions. Availability varies by region (ICB), and waiting lists can be very long. Private prescribing is also available following an online clinical assessment with a UK-licensed 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.