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 UK Price — Your Complete Guide to Weight Loss Injections
"Fat jabs" is the colloquial UK term for GLP-1 and GLP-1/GIP receptor agonist injections used for weight management. Three prescription-only options are currently licensed in the UK: Mounjaro (tirzepatide), Wegovy (semaglutide), and Saxenda (liraglutide). Each works differently, comes at different dose ranges, and has different costs depending on whether you access them through the NHS or privately. Understanding your options helps you make an informed decision with your GP or healthcare provider.
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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 Compared
Three prescription slimming injections are currently licensed in the UK for weight management. Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist — meaning it activates two hormone pathways simultaneously. Clinical trials showed participants lost an average of 15–21% of their body weight at the highest dose. It's administered as a once-weekly injection, with doses ranging from 2.5 mg to 15 mg.
Wegovy (semaglutide) is a GLP-1 agonist that activates a single hormone pathway. In clinical trials, it helped participants lose approximately 15% of body weight on average. It's also once-weekly, with doses from 0.25 mg to 2.4 mg. Saxenda (liraglutide), by contrast, is a daily injection (not weekly) at doses up to 3 mg, with similar average weight loss results to Wegovy.
- Mounjaro: once weekly, dual mechanism, 2.5–15 mg doses
- Wegovy: once weekly, single mechanism, 0.25–2.4 mg doses
- Saxenda: once daily, single mechanism, 0.6–3 mg doses
All three are prescription-only and require clinical assessment before being prescribed. Individual results vary significantly — these are average trial outcomes, not assures.
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.
NHS Access vs Private Cost
Accessing weight loss injections in the UK depends on your route. NHS access is through tier 3 specialist weight management services — you'll need a GP referral. Availability varies significantly by region (ICB), and waiting lists can be several months to over a year in many areas. If approved, the NHS covers the full cost.
Private access is available immediately through UK-licensed online prescribers and GPhC-registered pharmacies. Costs vary by medication and dose but typically range from £129–£320 per month depending on which injection and which dose strength you're prescribed. Private providers include established regulated services that require an online clinical assessment — no prescription means no dispensing.
- NHS: Free if approved through specialist service; significant waiting lists
- Private: £129–£320/month; immediate access with online assessment
Your GP can advise whether NHS referral is appropriate for you based on your BMI and health conditions.
- 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 uses a dual GIP+GLP-1 mechanism and is dosed once-weekly from 2.5–15 mg; Wegovy uses single GLP-1 mechanism, also once-weekly but dosed 0.25–2.4 mg. Clinical trials showed Mounjaro achieved slightly higher average weight loss (15–21% vs 15%), but individual results vary. Both require prescription.
Can I get fat jabs on the NHS?
Yes, if referred to a specialist tier 3 weight management service through your GP. You'll need a BMI of 30+ or 27+ with weight-related health conditions. Availability varies by region and waiting lists can be long. Your GP can advise on your eligibility and local services.
How much do weight loss injections cost privately in the UK?
Private costs typically range from £129–£320 per month depending on the medication and dose. Mounjaro and Wegovy are usually in the mid-to-upper range; Saxenda varies. Prices can differ between providers, so compare before committing. All require a prescription from a UK-licensed prescriber.
Is Saxenda cheaper than Mounjaro or Wegovy?
Saxenda pricing is often comparable to Wegovy, though it's a daily rather than weekly injection, which some people find less convenient. Price alone shouldn't determine choice — effectiveness, injection frequency, and side effect profile matter equally. Discuss options with your prescriber.
Do I need to change my diet and exercise if I use fat jabs?
Yes. Weight loss injections work best alongside a reduced-calorie diet and increased physical activity. They're not replacements for lifestyle changes — they're tools to support them. Clinical trials showed that participants combined medication with behavioural modifications for best results.
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.