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 Slimming Injections — Your UK Options Explained
Slimming injections are prescription-only weight loss medications now available through the NHS and private prescribing in the UK. Three main options are licensed for weight management: Mounjaro (tirzepatide), Wegovy (semaglutide), and Saxenda (liraglutide). All work by activating natural appetite-regulating hormones. Access varies significantly depending on whether you pursue NHS or private routes, and eligibility criteria apply. This guide explains all three options, how they differ, and how to access them in the UK.
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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 Injections — How They Compare
Mounjaro (tirzepatide) activates two hormone pathways — GIP and GLP-1 — making it a dual mechanism injection. It's administered once weekly in doses from 2.5 mg up to 15 mg. Clinical trials showed an average weight loss of approximately 15–21% of body weight over 72 weeks, though individual results vary significantly.
Wegovy (semaglutide) activates the GLP-1 pathway only. It's also a once-weekly injection, with doses ranging from 0.25 mg to the maximum 2.4 mg. In clinical trials, Wegovy supported an average weight loss of around 14.9% of body weight, alongside a reduced-calorie diet and increased physical activity.
Saxenda (liraglutide) is also a GLP-1 agonist but differs because it's a daily injection rather than weekly. Doses range from 0.6 mg to 3 mg once daily. All three are prescription-only and require a clinical assessment before being prescribed by a UK-licensed prescriber.
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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 Prescribing — Eligibility and Pathways
NHS access: Prescription weight loss injections, including Mounjaro and Wegovy, are available through specialist tier 3 and tier 4 weight management services. Eligibility typically requires a BMI of 30 or above, or 27–29.9 with weight-related health conditions like type 2 diabetes or cardiovascular disease. NHS access varies significantly by region — some areas have waiting lists of many months. Your GP can refer you to your local specialist weight management service.
Private prescribing: All three medications are available privately through GPhC-registered online pharmacies following an online clinical assessment with a UK-licensed prescriber. Private access doesn't require an NHS referral and is typically faster, though costs vary by dose and provider. A prescriber will assess your eligibility based on your individual health. Use our free BMI calculator above to check your starting point and understand where you fall on NHS eligibility thresholds.
- 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's the difference between Mounjaro and Wegovy?
Mounjaro is a dual GIP/GLP-1 agonist (once weekly, up to 15 mg), while Wegovy is a GLP-1 agonist only (once weekly, up to 2.4 mg). Both are injections, but clinical data suggests slightly different efficacy profiles. Both require a prescription and individual assessment. A prescriber can advise which suits your circumstances best.
Can I get weight loss injections on the NHS?
Yes, Mounjaro and Wegovy are now available through NHS specialist weight management services. Eligibility requires a BMI of 30+, or 27–29.9 with weight-related health conditions. Access varies by region, and waiting lists can be lengthy. Ask your GP for a referral to your local tier 3 or tier 4 weight management service.
What's the difference between daily and weekly injections?
Saxenda is a daily injection (liraglutide), while Mounjaro and Wegovy are once-weekly injections. Weekly injections are more convenient for many people as they require fewer doses. However, all three require consistent use as part of a broader weight management approach including diet and activity changes.
How do I know if I'm eligible for weight loss injections?
Eligibility typically requires a BMI of 30 kg/m² or above, or 27–29.9 with weight-related conditions (type 2 diabetes, high blood pressure, sleep apnoea, cardiovascular disease). South Asian, Chinese, Black African, and Black Caribbean adults may have lower thresholds. A GP or licensed prescriber will assess your individual eligibility following a clinical consultation.
How much weight will I lose with a slimming injection?
Clinical trials show average weight loss of 14–21% of body weight, but individual results vary significantly. Loss depends on your dose, diet, activity level, metabolism, and genetics. Our free GLP-1 weight loss calculator can help estimate potential outcomes at different doses, though only a prescriber can give you personalised guidance.
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.