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 for Weight Loss?
Fat injections, commonly called slimming injections or weight loss jabs in the UK, are prescription-only medicines that help regulate appetite and support weight management. They are not cosmetic injections — they are injectable medications containing active pharmaceutical ingredients that work through hormonal pathways. In the UK, these injections are licensed for adults with obesity or overweight with weight-related health conditions. They work best when combined with reduced-calorie diet and increased physical activity. This guide explains what they are, how they work, and what options are available through the NHS and 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.
Three UK-Licensed Weight Loss Injection Options
Three prescription weight loss injections are currently licensed in the UK. Mounjaro (tirzepatide) is a once-weekly injection that activates two hormone pathways — GIP and GLP-1 — to help regulate appetite and fullness. Clinical trials showed average weight loss of 15–21% of body weight over 72 weeks. Wegovy (semaglutide) is also a once-weekly injection that targets the GLP-1 pathway alone, with average weight loss around 15% over 68 weeks. Saxenda (liraglutide) is a once-daily injection, also GLP-1-based, with slightly less dramatic but still significant results. All three are prescription-only and require a clinical assessment before dispensing. They are not available over the counter, and eligibility depends on BMI and health conditions. Use our free BMI calculator above to check whether you may qualify for prescription weight loss treatment.
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
Weight loss injections work by mimicking natural hormones that regulate appetite, fullness signals, and blood sugar. GLP-1 receptor agonists activate the GLP-1 hormone pathway, which tells your brain you feel full after eating less food. They also slow how quickly food leaves your stomach, extending the feeling of fullness. Mounjaro adds a second mechanism by activating the GIP pathway as well, which may enhance appetite suppression. These hormonal effects help reduce food cravings and overall calorie intake naturally. Individual results vary significantly — some people experience substantial appetite reduction while others notice more modest effects. Weight loss injections are always used alongside a reduced-calorie diet and increased physical activity, not as a standalone treatment.
- 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 the same as cosmetic fat-dissolving injections?
No. Weight loss injections like Mounjaro and Wegovy are prescription medicines containing active pharmaceutical ingredients that work systemically through hormonal pathways. Cosmetic fat-dissolving injections (aqualyx, etc.) are different products designed for localised fat reduction and are not regulated as weight loss treatments. Weight loss injections are prescribed through NHS specialist services or private prescribers following clinical assessment.
How do I access weight loss injections in the UK?
Through two routes: NHS specialist weight management services (tier 3) — which requires GP referral and has longer waiting lists in most areas — or private online prescribing through a UK-licensed prescriber. Both routes require a clinical assessment to confirm eligibility based on your BMI and health conditions. Your GP can advise on NHS availability in your area.
What is the difference between GLP-1 and GIP/GLP-1 injections?
GLP-1 injections (Wegovy, Saxenda) activate one hormone pathway. GIP/GLP-1 injections (Mounjaro) activate two pathways simultaneously. The dual mechanism may provide stronger appetite suppression, and clinical trials showed slightly higher average weight loss with Mounjaro. However, individual results vary — response depends on your body's individual factors.
Do I need to use weight loss injections forever?
Weight loss injections are typically used for a defined period while you establish new eating and activity habits. Some people continue longer-term if they regain weight when stopping. Your prescriber will review your progress and discuss the best duration for your situation. Our free progress tracker can help you monitor your results over time.
Are weight loss injections available on the NHS for everyone?
No. NHS access is limited to specialist tier 3 weight management services, and availability varies significantly by region. General eligibility requires BMI ≥30 or BMI 27–29.9 with weight-related health conditions. Regional ICB budgets and waiting lists affect actual access. Private prescribing offers an alternative route without NHS referral, though costs apply.
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.