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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Fat Jabs Cost in the UK — What You Need to Know
"Fat jabs" is UK slang for prescription weight loss injections that help regulate appetite and support weight management. These are not cosmetic injections—they're licensed medicines that work by mimicking natural hormones. Three GLP-1 weight loss injections are available in the UK, each with different costs depending on whether you access them through the NHS or privately. Understanding what these injections are, how they work, and their pricing can help you make an informed decision about whether this treatment might be right for you alongside lifestyle changes.
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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.
Three UK-Licensed Weight Loss Injections
The three prescription slimming injections available in the UK are Mounjaro (tirzepatide), Wegovy (semaglutide), and Saxenda (liraglutide). Mounjaro and Wegovy are once-weekly injections, while Saxenda is injected daily. All three are GLP-1 medications (Mounjaro is a dual GIP/GLP-1 agonist) that work by signalling fullness to your brain and reducing appetite.
- Mounjaro: Starts at 2.5 mg, escalates to a maximum of 15 mg weekly. Private cost typically £180–£320 per month depending on dose.
- Wegovy: Starts at 0.25 mg, escalates to 2.4 mg maximum weekly. Private cost typically £129–£250 per month depending on dose.
- Saxenda: Daily injection, maximum 3 mg. Private cost typically £150–£250 per month.
All three require a prescription from a UK-licensed prescriber following a clinical assessment. None are available over-the-counter, and none are cosmetic treatments.
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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.
How GLP-1 Weight Loss Injections Work
GLP-1 medications work by mimicking a natural hormone your gut produces after eating. They signal your brain that you feel full, which may help reduce food cravings and support eating smaller portions. The medication also slows how quickly food leaves your stomach, prolonging the feeling of fullness after meals.
Clinical trials have shown that people using these injections alongside a reduced-calorie diet and increased physical activity may lose an average of 14–21% of their body weight over time—though individual results vary significantly. These injections are not a replacement for lifestyle changes; they work best as part of a comprehensive weight management approach. Your GP or a licensed prescriber can assess whether this treatment is suitable for your individual circumstances.
- 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 jabs the same as cosmetic injections?
No. Fat jabs are prescription medications, not cosmetic injections. They're GLP-1 receptor agonists—real medicines that regulate appetite hormones. Cosmetic fat-dissolving injections (like aqualyx) are unrelated treatments. Prescription weight loss injections require a clinical assessment and must be injected correctly by the user.
How much do weight loss injections cost on the NHS?
Access to weight loss injections through the NHS is limited and varies by region. They're available through specialist tier 3 weight management services, but waiting lists can be very long. Private prescribing costs typically £129–£320 per month depending on the medication and dose. Your GP can advise whether NHS access is available in your area.
What's the difference between Mounjaro, Wegovy, and Saxenda?
Mounjaro (tirzepatide) is a dual GIP/GLP-1 agonist with once-weekly dosing. Wegovy (semaglutide) is a GLP-1-only agonist, also once-weekly. Saxenda (liraglutide) is a daily GLP-1 injection. Clinical trials suggest Mounjaro and Wegovy may produce similar average weight loss (14–21%), though individual results vary. Your prescriber can help choose which is appropriate for you.
Who is eligible for weight loss injections in the UK?
You may be eligible if you have a BMI of 30 or above, or 27 or above with weight-related health conditions like type 2 diabetes, high blood pressure, or sleep apnoea. For South Asian, Chinese, Black African, or Black Caribbean adults, lower BMI thresholds apply. A prescriber will assess your individual suitability during a clinical consultation.
Do I need to keep taking fat jabs forever?
Not necessarily. Weight loss injections are typically used for a defined period—usually 12 weeks to several years depending on individual progress and prescriber guidance. Some people continue longer-term; others stop after reaching their goals. Stopping the medication may result in some weight regain if lifestyle changes aren't maintained. Your prescriber will discuss the right timeline for you.
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.