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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Mounjaro Weight Loss — What UK Adults Need to Know
Mounjaro (tirzepatide) is a prescription-only weight loss injection licensed in the UK for adults with excess weight or weight-related health conditions. It works by activating two natural hormone pathways to help regulate appetite and reduce food cravings. Clinical trials showed that people taking 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 how Mounjaro works, who may be eligible, and how to access it through the NHS or privately.
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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.
UK-Licensed Weight Loss Medications and Eligibility
Three prescription-only weight management medications are currently licensed in the UK:
- Mounjaro (tirzepatide) — dual GIP and GLP-1 receptor agonist, once-weekly injection, doses from 2.5 mg to 15 mg
- Wegovy (semaglutide) — GLP-1 receptor agonist, once-weekly injection, doses up to 2.4 mg
- Saxenda (liraglutide) — GLP-1 receptor agonist, daily injection, doses up to 3 mg
You may be eligible if you have a BMI of 30 or above, or a BMI of 27–29.9 with at least one weight-related health condition such as type 2 diabetes, prediabetes, high blood pressure, or cardiovascular disease. If you're of South Asian, Chinese, Black African, or Black Caribbean heritage, lower BMI thresholds may apply due to increased health risks at lower weights. A prescriber will assess your individual circumstances before recommending any medication. Use our free BMI calculator above to check your current BMI and understand where you fall within NHS weight categories.
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.
NHS Access vs Private Options — Which Route is Right for You?
NHS route: Mounjaro is approved for use within NHS specialist weight management services (tier 3 and tier 4). You'll need a referral from your GP to a specialist service in your area. Waiting times vary considerably by region—some areas have waiting lists of several months to over a year. Availability also depends on your local Integrated Care Board (ICB) funding decisions.
Private route: Available through GPhC-registered online pharmacies following an online clinical assessment with a UK-licensed prescriber. No NHS referral needed. Typically faster access but involves upfront costs (£129–£320+ per month depending on dose). Both routes require a clinical assessment to confirm suitability. Speak with your GP first to understand your options and NHS availability in your area.
- 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 much weight might I lose with Mounjaro?
Clinical trials (SURMOUNT-1) showed average weight loss of 15–21% of body weight over 72 weeks on Mounjaro 15 mg, alongside diet and activity changes. Individual results vary significantly based on starting weight, adherence, diet, and exercise. Some people lose more, others less. It's not clinically studied weight loss—it's a tool that may help you achieve your goals alongside lifestyle changes.
What's the difference between Mounjaro and Wegovy?
Both are once-weekly injections for weight management. Mounjaro is a dual GIP+GLP-1 agonist (higher average weight loss in trials), while Wegovy is a GLP-1 agonist only. Mounjaro starts at 2.5 mg, Wegovy at 0.25 mg. Maximum doses are 15 mg vs 2.4 mg respectively. They work slightly differently but both are prescription-only and require clinical assessment. Your prescriber will advise which is more suitable for you.
Can I get Mounjaro on the NHS?
Yes, Mounjaro is approved for NHS use through specialist tier 3/4 weight management services. However, you need a GP referral and access varies significantly by region. Many areas have long waiting lists. Private options are available faster but involve cost. Contact your GP to discuss NHS availability in your area and alternative options.
What are the most common side effects?
Most common side effects include nausea, diarrhoea, vomiting, constipation, and stomach pain—usually mild and temporary. These often improve as your body adjusts. Injection site reactions (redness, bruising) can occur. Serious side effects are rare but include severe stomach pain (possible pancreatitis) and gallbladder problems. Always report any concerning symptoms to your prescriber immediately.
How do I find out if I'm eligible for weight loss medication?
Start by calculating your BMI using our free BMI calculator above. If your BMI is 30+, or 27–29 with weight-related health conditions, you may be eligible. Book an appointment with your GP to discuss your options—they can refer you to NHS specialist services or advise on private routes. Try our GLP-1 weight loss calculator to explore potential outcomes at different doses based on 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.