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 is a prescription-only weekly weight loss injection that works differently from other slimming medications. It activates two natural hormone pathways—GIP and GLP-1—to reduce appetite, support feeling fuller after meals, and slow how quickly food leaves your stomach. Clinical trials showed participants lost an average of 15–21% of their body weight alongside a reduced-calorie diet and increased physical activity. But how do you access it in the UK, and what does it cost? This guide explains the mechanism, how to get it, and what you'll pay.
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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 Works — The Science of Weight Loss
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist—the first of its kind approved for weight management in the UK. This dual action sets it apart from other weekly weight loss injections like Wegovy (semaglutide), which works through GLP-1 alone.
How it helps you lose weight:
- Reduces appetite and food cravings by signalling fullness to your brain
- Slows gastric emptying—the rate food leaves your stomach—so you feel satisfied longer
- Regulates how your body uses fat and stores glucose
- Reduces overall calorie intake without requiring willpower alone
In the SURMOUNT-1 clinical trial, participants on Mounjaro 15mg lost an average of 20.9% of their body weight over 72 weeks. Individual results vary significantly, and these results were achieved alongside lifestyle changes—not medication alone. To estimate your potential weight loss outcomes, try our GLP-1 weight loss calculator, which helps you project results at different Mounjaro doses.
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.
Accessing Mounjaro in the UK — NHS vs Private Routes
In the UK, you can access Mounjaro through two routes:
- NHS: Through specialist tier 3/4 weight management services. NICE has approved tirzepatide for NHS use, but access varies significantly by region (ICB) and availability is often limited. Your GP must refer you to your local specialist weight management service. Waiting lists can be months or years in some areas.
- Private: Through an online consultation with a UK-licensed prescriber. If approved, your prescription is dispensed by a GPhC-registered pharmacy. Private access is available without NHS referral and typically costs £150–£320 per month depending on your dose. Online consultations usually cost £20–£50 and take 10–15 minutes.
To check eligibility, calculate your BMI using our free BMI calculator above. You'll need a BMI of 30 or above, or 27 or above with weight-related health conditions such as type 2 diabetes or high blood pressure.
- 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 is the difference between Mounjaro and Wegovy?
Both are once-weekly injections for weight loss, but Mounjaro is a dual GIP and GLP-1 agonist, while Wegovy (semaglutide) is a GLP-1 agonist only. In clinical trials, Mounjaro achieved slightly higher average weight loss (20.9% vs 14.9%), though individual results vary. Both are prescription-only and require clinical assessment.
How much does Mounjaro cost privately in the UK?
Private Mounjaro costs typically range from £150–£320 per month depending on your dose and provider. Starting doses (2.5–5mg) are generally cheaper than maximum doses (15mg). Online consultation fees are usually £20–£50 additional. Prices vary by pharmacy, so it's worth comparing.
Can I get Mounjaro on the NHS in the UK?
Yes, NICE has approved tirzepatide (Mounjaro) for NHS use through specialist weight management services. However, access is limited and varies significantly by region. Your GP must refer you to your local tier 3 service. Waiting lists can be very long—in some areas, several months to years. Private access is often faster.
How quickly will I lose weight on Mounjaro?
Weight loss typically begins within the first 4 weeks, with noticeable results by 8–12 weeks. Average loss is around 0.5–1kg per week, though this varies. Clinical trials showed average loss of 20.9% over 72 weeks. Results depend on your starting weight, dose, diet, and exercise. Track your progress using our free progress tracker.
Is Mounjaro available without a prescription?
No, Mounjaro is prescription-only in the UK. You must have a clinical assessment by a UK-licensed prescriber before being prescribed. This can be done through NHS specialist services or a private online consultation. Never buy without a prescription from an unregistered source.
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.