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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How to Get a Slimming Jab in the UK
A slimming jab is a prescription weight loss injection licensed in the UK to help manage excess weight. The most common options are GLP-1 receptor agonist medications and dual GIP/GLP-1 agonists like Mounjaro and Wegovy, which may help reduce appetite and support weight loss alongside diet and exercise. You can access these injections through two main routes in the UK: the NHS (via GP referral to specialist services) or privately through an online consultation with a licensed prescriber. Both routes require a clinical assessment to confirm you're eligible.
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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 Can Get a Slimming Jab? UK Eligibility Criteria
To be eligible for prescription weight loss injections in the UK, you must meet specific BMI and health criteria. Standard eligibility: a BMI of 30 kg/m² or above, or a BMI of 27–29.9 kg/m² with at least one weight-related health condition. Weight-related conditions include type 2 diabetes, prediabetes, high blood pressure, abnormal blood fats, obstructive sleep apnoea, or previous heart attack or stroke.
Lower thresholds apply if you are of South Asian, Chinese, Black African, or Black Caribbean heritage — your GP or prescriber will discuss this with you, as these groups face higher health risks at lower BMI levels.
You cannot access slimming injections if you are under 18, pregnant or breastfeeding, or have a severe allergy to the medication ingredients. Use our free BMI calculator above to check where you stand, and discuss your results with your GP for personalised advice.
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 Slimming Injections in the UK
NHS route: Ask your GP for a referral to your local tier 3 (or tier 4) specialist weight management service. The service will assess you for suitability and may prescribe weight loss injections if you meet criteria. This route is free but involves waiting lists — some regions have significant delays of several months.
Private route: Use a GPhC-registered online pharmacy. You'll have a consultation with a UK-licensed prescriber via the platform. If approved, a prescription is issued and the medication is dispensed. This is faster but involves a cost (typically £129–£320 monthly depending on dose). Both routes require genuine clinical assessment — there are no shortcuts.
Try our GLP-1 weight loss calculator to explore projected outcomes and understand what to expect from 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.
What exactly is a slimming jab or "fat jab"?
A slimming jab is a prescription-only weight loss injection containing GLP-1 or GIP/GLP-1 receptor agonist medication. These drugs mimic natural hormones that regulate appetite and blood sugar, helping you feel fuller and reducing food cravings. Common UK options include Mounjaro (tirzepatide), Wegovy (semaglutide), and Saxenda (liraglutide). All require a prescription and clinical assessment.
How long does it take to get a slimming jab through the NHS?
Waiting times vary significantly by region and NHS integrated care board. Some areas have waiting lists of 6–12 months or longer for tier 3 weight management services. Private routes are typically faster — you can often be approved and start treatment within 1–2 weeks. Ask your GP about current waiting times in your area.
What happens during a private online consultation for a slimming jab?
You'll complete a health questionnaire covering your weight, medical history, medications, and lifestyle. A UK-licensed prescriber reviews your information and may request additional details. If you're eligible, they issue a prescription. The entire process usually takes 24–48 hours. You'll discuss treatment expectations, side effects, and storage before starting.
Are slimming injections expensive on the NHS versus private?
On the NHS, slimming injections are free if prescribed through specialist services — but you must meet criteria and go through the referral pathway. Privately, costs range from roughly £129–£320 per month depending on the medication and dose. Some private providers offer subscription packages or lower rates at higher doses.
Can my GP prescribe slimming injections directly without referral?
Generally, no. Most GPs cannot prescribe weight loss injections directly in the UK — they must refer you to a tier 3 specialist weight management service. However, some integrated care boards now permit GPs to initiate treatment following specialist guidance. Ask your GP whether this is available in your area, or consider the private route for faster access.
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.