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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NHS Fat Loss Injections — What Are Your Options?
Fat loss injections are prescription-only medicines licensed in the UK that may help support weight management in adults. Currently, three GLP-1 and GLP-1/GIP medications are available on the NHS and through private prescribing: Mounjaro (tirzepatide), Wegovy (semaglutide), and Saxenda (liraglutide). Each works differently and has different injection schedules. This guide explains how they work, who can access them, and the differences between NHS and private routes in the UK.
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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.
Comparing UK-Licensed Weight Loss Injections
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist — the newest option for GLP-1 weight loss in the UK. It's injected once weekly and available in doses from 2.5 mg to 15 mg. Clinical trials showed average weight loss of around 15–21% of body weight, though individual results vary significantly.
Wegovy (semaglutide) is a GLP-1 receptor agonist injected once weekly, with a maximum dose of 2.4 mg. Clinical evidence demonstrated average weight loss of approximately 15% of body weight in trials. It's been available longer than Mounjaro in the UK and has extensive real-world use data.
Saxenda (liraglutide) is also a GLP-1 agonist but requires a daily injection rather than weekly. The maximum dose is 3 mg daily. It has been available for longer but is used less frequently than Mounjaro or Wegovy due to the daily injection requirement.
All three are prescription-only medicines requiring clinical assessment before prescription. None are cosmetic products — they are licensed weight management medications.
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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 Access vs Private Access in the UK
NHS access: Fat loss injections are available through specialist NHS tier 3 and tier 4 weight management services. Your GP can refer you, but access varies significantly by region and NHS integrated care board (ICB). Waiting lists for specialist services can be several months to over a year in many areas. When prescribed through the NHS, there is no direct cost to you at the point of prescription.
Private access: All three medications are available through private online consultations with UK-licensed prescribers. You'll complete an online health assessment, and if approved, a prescription is issued and dispensed by a GPhC-registered pharmacy. This route typically has shorter waiting times but involves costs ranging from approximately £129–£320 monthly depending on dose and provider.
Eligibility: Both routes require a BMI of 30 or above, or 27–29.9 with weight-related health conditions such as type 2 diabetes, high blood pressure, or cardiovascular disease. A prescriber will assess suitability individually.
- 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.
Can I get fat loss injections on the NHS?
Yes, Mounjaro, Wegovy, and Saxenda are available through NHS specialist weight management services. Your GP can refer you to your local tier 3 service. However, availability and waiting times vary significantly across the UK by region. Many areas have substantial waiting lists, and not all ICBs may offer all three options.
What's the difference between Mounjaro and Wegovy?
Mounjaro is a dual GIP/GLP-1 agonist (weekly injection, up to 15 mg). Wegovy is a GLP-1 agonist only (weekly injection, up to 2.4 mg). Clinical trials showed similar average weight loss percentages, though some evidence suggests Mounjaro may have a slightly larger effect. Individual results vary significantly, and choice depends on prescriber assessment and availability.
How quickly do fat loss injections work?
Weight loss typically begins within the first month and continues over 12–16 weeks as doses are increased gradually. Most significant results appear after 3–6 months of treatment. However, results vary between individuals. These medications work best alongside reduced-calorie diet and increased physical activity — they're not standalone treatments.
Are these weight loss injections safe?
All three are licensed medicines approved by the MHRA for weight management in adults. They have undergone safety testing. Common side effects include nausea, vomiting, and constipation — typically mild and manageable. Serious side effects are rare but include pancreatitis symptoms (severe stomach pain) and gallbladder issues. Your prescriber will assess individual safety before prescribing.
Can I use the BMI calculator to check my eligibility?
Yes — use our free BMI calculator above to check your BMI. If your result is 30 or above (or 27–29.9 with a weight-related health condition), you may be eligible for prescription weight loss treatment. A GP or licensed prescriber will then assess you individually to confirm suitability. Calculate your weight loss projection using our GLP-1 weight loss calculator as well.
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.