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
How Do Slimming Injections Work?
Slimming injections, also called weight loss jabs or fat jabs, are prescription medications that help reduce appetite and support sustainable weight loss. In the UK, the main weight loss injections are GLP-1 receptor agonists like Wegovy (semaglutide) and dual GIP/GLP-1 medications like Mounjaro (tirzepatide). These work by mimicking natural hormones that signal fullness to your brain, slow how quickly food leaves your stomach, and help regulate blood sugar. They're licensed for adults with obesity or overweight with health conditions, and are available through both NHS specialist services and private online prescribing 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's Eligible for Slimming Injections in the UK?
Eligibility for prescription slimming injections in the UK is based on BMI thresholds and weight-related health conditions. You may qualify if you have:
- A BMI of 30 kg/m² or above (obesity), OR
- A BMI of 27–29.9 kg/m² with at least one weight-related health condition such as type 2 diabetes, prediabetes, high blood pressure, abnormal blood fats, sleep apnoea, or heart disease history
If you're of South Asian, Chinese, Black African, or Black Caribbean heritage, the NHS recommends lower BMI thresholds — you may qualify at BMI 27.5 or above. This is because these groups face higher cardiovascular and diabetes risks at lower weights. Your GP or prescriber will assess your individual circumstances during a clinical consultation. You cannot access these medications if you're under 18, pregnant, breastfeeding, or have certain medical conditions like severe stomach problems.
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 vs Private Routes — How to Get Slimming Injections
NHS access: Referral to a tier 3 specialist weight management service through your GP is the first step. NHS teams assess eligibility and manage ongoing prescriptions, but waiting lists vary significantly by region — some areas have waits of several months or longer. Private access is faster: you complete an online consultation with a UK-licensed prescriber, and if approved, the prescription is dispensed by a registered pharmacy. Both routes require a clinical assessment before any medication is provided. You can also use our free GLP-1 weight loss calculator to understand projected outcomes at different doses, and the BMI calculator to check whether you meet eligibility thresholds. Either way, weight loss injections work best alongside a reduced-calorie diet and increased physical activity.
- 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 slimming injections and Ozempic?
Both Wegovy and Ozempic contain semaglutide, but Ozempic is licensed for type 2 diabetes (up to 2 mg dose), while Wegovy is the licensed weight loss version (up to 2.4 mg). Mounjaro (tirzepatide) is a dual GIP/GLP-1 injection that's also approved for weight management in the UK. All are prescription-only and require clinical assessment.
How quickly will I lose weight with slimming injections?
Clinical trials show average weight loss of 15–21% body weight over several months, but individual results vary significantly. The NHS recommends losing 0.5–1 kg per week as a safe, sustainable rate. Results depend on dose, diet adherence, physical activity, and individual factors. Your prescriber will monitor your progress.
Can I get slimming injections on the NHS?
Yes, through specialist tier 3 weight management services. You'll need a GP referral and an assessment to confirm eligibility. Availability and waiting times vary by region and local NHS funding. Ask your GP about tier 3 services in your area.
What are the main side effects of slimming injections?
Very common side effects include nausea, diarrhoea, constipation, and stomach pain, particularly when starting or increasing dose. Most improve over time. Serious side effects are rare but include severe stomach pain (possible pancreatitis) and allergic reactions. Your prescriber will discuss all risks before you start.
How do slimming injections actually make you feel less hungry?
They mimic GLP-1 and GIP — natural hormones your gut produces after eating. These hormones tell your brain you're full, reduce food cravings, and slow stomach emptying so food stays in your stomach longer, prolonging the feeling of fullness. This makes eating less feel more natural.
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.