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
Are Fat Jabs Safe — And How to Access Them in the UK
Fat jabs—the colloquial UK term for weight loss injections—are prescription medications that have been approved for weight management by UK medical authorities. They work by activating natural hormone pathways that help regulate appetite and support feeling fuller after smaller meals. Safety depends on proper medical assessment, appropriate use, and individual health circumstances. This guide explains how fat jabs work, who may be eligible, and how to access them safely through either NHS services or private consultations 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.
Who Is Eligible for Weight Loss Injections in the UK?
Weight loss injections are prescription-only medicines available to UK adults meeting specific eligibility criteria. You may be considered for treatment if you have a BMI of 30 kg/m² or above, or a BMI of 27–29.9 kg/m² alongside at least one weight-related health condition such as type 2 diabetes, prediabetes, high blood pressure, abnormal blood fats, obstructive sleep apnoea, or cardiovascular disease history.
For South Asian, Chinese, Black African, or Black Caribbean adults: Lower BMI thresholds apply due to higher health risks at lower weights. You may be eligible with a BMI of 27.5 or above.
- You must be at least 18 years old
- Not pregnant, planning pregnancy, or breastfeeding
- Without severe digestion problems or contraindications
- Willing to combine treatment with diet and lifestyle changes
Use our free BMI calculator above to check where you currently fall, then discuss eligibility with your GP or a licensed prescriber.
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.
Two Routes to Access Fat Jabs: NHS vs Private
NHS Route: Ask your GP for referral to your local tier 3 specialist weight management service. NHS prescription slimming injections are available but waiting lists vary significantly by region—some areas have waits of several months. Once assessed by the specialist team, you can be prescribed GLP-1 weight loss injections if appropriate.
Private Route: Faster access through online consultation with a UK-licensed prescriber. Following a clinical assessment questionnaire, a prescriber determines suitability and issues a prescription to a GPhC-registered pharmacy. No NHS referral needed. Costs typically range from £129–£320 monthly depending on dose. Both routes require proper medical assessment—never access weight loss injections without a valid prescription from a qualified prescriber.
- 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 are fat jabs and how do they work?
Fat jabs are prescription weight loss injections containing GLP-1 or GIP/GLP-1 receptor agonists. These medications mimic natural hormones that regulate appetite, slow stomach emptying, and help you feel fuller after smaller meals. Common UK fat jabs include Mounjaro (tirzepatide), Wegovy (semaglutide), and Saxenda (liraglutide). They're administered weekly or daily depending on the medication.
Are weight loss injections safe for everyone?
Weight loss injections are safe for many people when prescribed appropriately, but not everyone. You cannot use them if pregnant, breastfeeding, allergic to the active ingredient, or if you have severe pancreas or gallbladder conditions. A prescriber will assess your individual health before issuing a prescription. Common side effects include nausea, diarrhoea, and constipation—usually mild and temporary.
How long do you stay on fat jabs?
Treatment duration varies individually. Some people use them for several months to a year, others longer-term. Your prescriber will review progress regularly and decide whether to continue, adjust dose, or stop treatment. Weight loss injections work best alongside sustained diet and exercise changes—they're not a permanent solution but a tool to support healthier habits.
Can I get fat jabs on the NHS in the UK?
Yes, but availability is limited. You need referral from your GP to a tier 3 specialist weight management service. Eligibility and waiting times vary significantly by region (ICB). Some areas have long waiting lists. Eligibility requires BMI of 30+ (or 27–29.9 with health conditions), and you must be willing to engage with lifestyle support alongside medication.
What's the difference between NHS and private weight loss injections?
Both routes prescribe the same medications (Mounjaro, Wegovy, Saxenda), but NHS access requires GP referral and typically involves waiting lists, while private consultations are faster (often within days). Private costs £129–£320+ monthly. Both require clinical assessment by a qualified prescriber. Neither route is "safer"—both ensure proper medical oversight. Choose based on urgency and budget.
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.