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
What Are Fat Injections on the NHS?
Fat injections—often called slimming injections or weight loss jabs in the UK—are prescription-only medicines designed to help adults manage excess weight. These are not cosmetic injections; they are licensed pharmaceutical treatments that work by mimicking natural hormones to regulate appetite and support weight loss alongside dietary changes and physical activity. In the UK, several GLP-1 weight loss injections are available through NHS specialist services and private prescribing, with eligibility based on BMI and health factors. Use our free BMI calculator to check where you currently stand, then explore whether prescription weight loss treatment might be suitable for you.
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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.
Three UK-Licensed Weight Loss Injections
Three prescription weight loss injections are currently licensed in the UK:
- Mounjaro (tirzepatide) – A once-weekly injection that activates two hormone pathways (GIP and GLP-1), helping regulate appetite and fullness signals. Doses range from 2.5 mg to 15 mg weekly. In clinical trials, patients lost an average of 15–21% of body weight over 72 weeks alongside lifestyle changes.
- Wegovy (semaglutide) – A once-weekly GLP-1 injection with doses from 0.25 mg to 2.4 mg. Clinical trials showed average weight loss of approximately 15% of body weight at the maximum dose.
- Saxenda (liraglutide) – A once-daily GLP-1 injection (3 mg maximum). It has been available longer than Mounjaro and Wegovy, though it requires daily administration rather than weekly.
All three are prescription-only medicines that require a clinical assessment before being prescribed. Individual results vary significantly based on adherence to treatment, dietary changes, and physical activity levels.
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.
How Weight Loss Injections Work
GLP-1 receptor agonist medications (Wegovy and Saxenda) and the dual GIP/GLP-1 agonist (Mounjaro) mimic hormones your body naturally produces after eating. These injections signal to your brain that you are full, reducing appetite and food cravings, which helps you eat smaller portions and feel satisfied sooner. They also slow how quickly food leaves your stomach, prolonging the feeling of fullness. These are not fat-dissolving injections—they are not cosmetic treatments. They work systemically to support weight management when combined with a reduced-calorie diet and increased physical activity. Try our free GLP-1 weight loss calculator to explore potential weight loss projections at different doses.
- 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.
Are fat injections available on the NHS?
Yes, GLP-1 weight loss injections are available on the NHS through specialist tier 3/4 weight management services. However, availability varies significantly by region and waiting lists can be lengthy. You need a GP referral to specialist services. Private prescribing is also available without NHS referral through registered online prescribers.
What is the difference between fat injections and cosmetic fat-dissolving injections?
Weight loss injections are prescription medicines that work systemically to regulate appetite. Cosmetic fat-dissolving injections (like aqualyx) are non-regulated aesthetic treatments injected directly into fat deposits. They are entirely different—weight loss injections are pharmaceutical treatments requiring clinical assessment.
Who is eligible for weight loss injections on the NHS?
NHS eligibility typically requires a BMI of 30 or above, or 27–29.9 with a weight-related health condition (diabetes, high blood pressure, sleep apnoea, cardiovascular disease). Lower thresholds apply for adults of South Asian, Chinese, Black African, or Black Caribbean heritage. Your GP assesses individual eligibility.
How much weight can you lose with fat injections?
Clinical trials show average weight loss of 15–21% of body weight over several months, depending on the medication and dose. However, individual results vary significantly. Weight loss depends on adherence to the injection schedule, adopting a reduced-calorie diet, and increasing physical activity. Results are not assured.
Are there side effects from weight loss injections?
Yes. Common side effects include nausea, diarrhoea, constipation, and stomach pain, especially when starting or increasing doses. These often improve over time. Serious side effects are rare but can include pancreatitis or gallbladder problems. Your prescriber discusses all risks before starting 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.