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 Help You Lose Weight?
Mounjaro (tirzepatide) is a prescription-only weekly weight loss injection that works by activating two natural hormone pathways in your body. Unlike other weight loss medications, Mounjaro is a dual GIP and GLP-1 receptor agonist, which means it works on both appetite regulation and how your body processes food. Clinical trials showed that people using Mounjaro alongside a reduced-calorie diet and increased physical activity lost an average of 15–21% of their body weight — though individual results vary significantly. This guide explains the mechanism, NHS eligibility in the UK, and what to expect.
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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's Dual Mechanism Works
Mounjaro activates two hormone pathways: GIP (glucose-dependent insulinotropic polypeptide) and GLP-1 (glucagon-like peptide-1). Both are naturally produced in your gut after eating.
- GLP-1 action: Signals to your brain that you are full, reducing appetite and food cravings. It also slows how quickly food leaves your stomach, helping you feel satisfied longer after smaller meals.
- GIP action: Enhances the body's ability to regulate how it uses glucose and fat, supporting metabolic function.
- Combined effect: This dual approach may provide more powerful appetite suppression than single-mechanism medications like Wegovy (semaglutide).
The SURMOUNT-1 clinical trial found that at the maximum dose of 15 mg weekly, Mounjaro helped participants lose an average of 20.9% of body weight over 72 weeks. However, weight loss depends on adherence to the medication, dietary changes, and physical activity — Mounjaro is not a replacement for lifestyle changes but works alongside them.
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.
Mounjaro, NHS Eligibility, and UK Access Routes
In the UK, adults with a BMI of 30 kg/m² or above, or BMI of 27–29.9 kg/m² with weight-related health conditions (such as type 2 diabetes, prediabetes, high blood pressure, or sleep apnoea), may be eligible for Mounjaro. NHS access: Available through specialist tier 3 weight management services — your GP can refer you, though waiting lists vary significantly by region. Private access: Available through a GPhC-registered online pharmacy following a clinical assessment with a UK-licensed prescriber. Check your personal BMI and eligibility using our free BMI calculator above, then discuss options with your GP or a prescriber. Results with Mounjaro are highly individual — tracking your progress with our free progress tracker can help monitor your personal journey.
- 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.
How quickly does Mounjaro work for weight loss?
Weight loss typically becomes noticeable within the first 4–8 weeks, though individual responses vary. The medication is titrated slowly over 20 weeks from 2.5 mg to a maintenance dose, allowing your body to adjust. Most significant weight loss occurs between weeks 8–16 once you reach a therapeutic dose.
Is Mounjaro available on the NHS in the UK?
Yes, Mounjaro (tirzepatide) is approved by NICE and available on the NHS through specialist tier 3 weight management services. However, availability and waiting times vary by region and NHS ICB. Your GP can assess your eligibility and refer you if appropriate.
What's the difference between Mounjaro and Wegovy for weight loss?
Both are prescription-only weekly injections for weight loss in the UK. Mounjaro is a dual GIP/GLP-1 agonist (up to 15 mg), while Wegovy is a single GLP-1 agonist (up to 2.4 mg). Clinical trial data suggests Mounjaro may produce slightly greater average weight loss, but individual results vary. Your prescriber will advise which is suitable for you.
Can I get Mounjaro privately in the UK while waiting for NHS assessment?
Yes. Mounjaro is available privately through UK-licensed online prescribers and GPhC-registered pharmacies following a clinical assessment. Costs vary by dose and provider (typically £129–£280 per month). You do not need an NHS referral to access it privately.
Will I keep the weight off once I stop Mounjaro?
Weight loss from Mounjaro is sustained while taking the medication alongside lifestyle changes. If you stop Mounjaro without maintaining the dietary and activity changes, weight regain is common. Your prescriber will discuss long-term management and whether continued treatment is appropriate for your circumstances.
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.