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
What Are Diet Injections on the NHS?
Diet injections, commonly called slimming injections or weight loss jabs in the UK, are prescription-only medicines that help regulate appetite and support weight management. Three medications are currently licensed for weight management in the UK on the NHS: Mounjaro (tirzepatide), Wegovy (semaglutide), and Saxenda (liraglutide). These are not cosmetic injections—they are pharmaceutical treatments that work by activating natural hormone pathways in the body. They're prescribed as part of a structured weight management programme alongside dietary changes and increased physical activity. Try our GLP-1 weight loss calculator to explore how these medications may work for different body types.
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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.
Three NHS-Licensed Weight Loss Injections Explained
Mounjaro (tirzepatide) is a once-weekly injection that works as a dual GIP and GLP-1 receptor agonist—meaning it activates two natural hormone pathways to help regulate appetite, reduce food cravings, and support feeling fuller after meals. Clinical trials showed average weight loss of around 15–21% of body weight when used alongside a reduced-calorie diet and exercise.
Wegovy (semaglutide) is also a once-weekly injection but activates only the GLP-1 pathway. It helps reduce appetite and supports a feeling of fullness, with clinical trials showing average weight loss of approximately 15% of body weight over 68 weeks.
Saxenda (liraglutide) is a daily injection (not weekly) that also works as a GLP-1 agonist. All three are prescription-only and require a clinical assessment before being prescribed. NHS access is through specialist tier 3 or tier 4 weight management services, though availability varies significantly by region. Use our free BMI calculator above to check your starting point and understand your weight context before discussing options with your GP.
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.
How GLP-1 Weight Loss Injections Work
GLP-1 receptor agonists mimic a natural hormone your body produces after eating. This hormone signals to your brain that you're full, helping reduce overall appetite and food cravings. The injections also slow how quickly food leaves your stomach—meaning you feel satisfied after eating smaller portions. This is different from cosmetic or fat-dissolving injections, which work on tissue directly. Weight loss injections are pharmaceutical treatments that work internally to regulate appetite hormones.
Results vary between individuals based on genetics, lifestyle, diet adherence, and exercise. These medications are most effective when combined with a calorie deficit and increased physical activity. Track your progress with our free progress tracker as you work towards your health goals.
- 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 slimming injections available on the NHS for everyone?
No. NHS slimming injections are typically available through specialist weight management services (tier 3 or 4) for adults with a BMI of 30 or above, or 27–29.9 with weight-related health conditions like type 2 diabetes or high blood pressure. Access varies significantly by region and waiting lists can be lengthy. Your GP can assess your eligibility and refer you to specialist services.
What's the difference between Mounjaro, Wegovy, and Saxenda?
Mounjaro is a once-weekly dual GIP and GLP-1 agonist. Wegovy is a once-weekly GLP-1 agonist only. Saxenda is a daily GLP-1 injection. Clinical trial data shows slightly higher average weight loss with Mounjaro (15–21%) compared to Wegovy (15%), though individual results vary significantly. Your prescriber will assess which is most appropriate for you.
Are diet injections the same as cosmetic fat injections?
No. Diet injections (GLP-1 medications) are pharmaceutical treatments taken internally to regulate appetite hormones. Cosmetic fat-dissolving injections work on tissue directly and are a different type of procedure. Diet injections are prescription-only medicines requiring clinical assessment and medical oversight.
How much weight can I expect to lose with a diet injection?
Clinical trials show average weight loss of 15–21% of body weight, but individual results vary significantly. Some people lose more, some less. Weight loss depends on your starting weight, diet adherence, physical activity, genetics, and how your body responds. Always use conditional language—your prescriber can give you more personalised expectations.
Can I get diet injections through the NHS if I'm on a waiting list?
NHS access is through specialist weight management services and varies by region. Some areas have shorter waiting lists than others. If you're waiting for NHS access, your GP can advise on timelines for your local health system. Private prescribing is also available in the UK without an NHS referral, though this involves private costs. ```
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.