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 Slimming Jabs: What You Need to Know in the UK
Mounjaro is a prescription-only weight management injection licensed in the UK that may help adults lose weight alongside a reduced-calorie diet and increased physical activity. Often called "slimming jabs" or "fat jabs" in the UK, Mounjaro (tirzepatide) works by activating two natural hormone pathways to help regulate appetite and support weight loss. Access is available through NHS specialist services or private online prescribing following a clinical assessment. Individual results vary significantly, and it's important to understand how NHS eligibility works and what to expect from this medication.
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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.
NHS Eligibility and How Mounjaro Slimming Jabs Are Prescribed
In the UK, Mounjaro may be prescribed through NHS tier 3 specialist weight management services for adults who meet specific eligibility criteria. You typically need a BMI of 30 kg/m² or above, or 25–29.9 with at least one weight-related health condition such as type 2 diabetes, high blood pressure, or sleep apnoea. For South Asian, Chinese, Black African, or Black Caribbean adults, lower BMI thresholds apply — eligibility may start at BMI 27.5 or above due to higher health risks at lower weights.
Mounjaro is a dual GIP and GLP-1 receptor agonist — different from other weight loss injections because it activates two hormone pathways rather than one. In clinical trials, participants lost an average of 15–21% of their body weight over 72 weeks, though individual results vary and outcomes depend on lifestyle changes, dose, and personal factors. The medication is injected once weekly using a KwikPen device, starting at 2.5 mg and increasing gradually to a maximum of 15 mg over several months.
NHS access involves referral from your GP to a specialist weight management service, which assesses your eligibility and manages your treatment. Availability and waiting times vary significantly across UK regions — some areas have substantial waiting lists.
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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 vs Private Access: Getting Mounjaro in the UK
NHS route: Free at point of use, but requires a GP referral to a tier 3 specialist service. Assessment takes place in a multidisciplinary clinic, and prescribing follows NICE guidance. However, NHS access is limited by regional availability and capacity — waiting lists in some areas can be several months or longer.
Private route: Available through GPhC-registered online pharmacies following a consultation with a UK-licensed prescriber. No NHS referral needed, faster access, but costs approximately £129–£320 per month depending on dose. Both routes require a clinical assessment to confirm the medication is appropriate for you. Use our GLP-1 weight loss calculator above to estimate potential outcomes, and our BMI calculator to check whether you may meet eligibility criteria. Your GP or prescriber will give you final personalised advice.
- 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 exactly are slimming jabs and how do they work?
Slimming jabs is the UK term for prescription weight loss injections like Mounjaro (tirzepatide). Mounjaro works by mimicking two natural hormones — GIP and GLP-1 — which help regulate appetite, reduce cravings, and support feeling fuller after smaller meals. It slows how quickly food leaves your stomach and helps your body manage blood sugar and fat use more effectively.
Am I eligible for Mounjaro on the NHS?
You may be eligible if you have a BMI of 30 or above, or 27–29.9 with a weight-related health condition like type 2 diabetes or high blood pressure. For South Asian, Chinese, Black African, or Black Caribbean adults, lower BMI thresholds apply (27.5+). Your GP can assess whether you meet NHS criteria and refer you to a specialist weight management service.
How much weight can I expect to lose with Mounjaro?
Clinical trials showed participants lost an average of 15–21% of their body weight over 72 weeks, but individual results vary significantly. Weight loss depends on your starting weight, the dose you reach, how well you stick to a reduced-calorie diet, and physical activity. Your prescriber can help estimate realistic outcomes for your situation.
What's the difference between NHS and private Mounjaro in the UK?
NHS Mounjaro is free but requires a GP referral and specialist assessment, with variable waiting times by region. Private Mounjaro is accessed through online prescribing with faster availability but costs approximately £129–£320/month. Both require clinical assessment; ask your GP about NHS options first.
What are the common side effects of Mounjaro slimming jabs?
Very common side effects include nausea, diarrhoea, constipation, stomach pain, and vomiting — especially when starting or increasing doses. Most ease over time as your body adjusts. Uncommon side effects include headache, fatigue, and hair loss. Seek urgent help for severe stomach pain or signs of pancreatitis. Your prescriber will monitor you throughout treatment.
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.