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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Diet Injections Available on the NHS
Diet injections, also called weight loss injections or slimming injections, are prescription-only medicines available in the UK for adults meeting specific eligibility criteria. Three medications are currently licensed for weight management: Mounjaro (tirzepatide), Wegovy (semaglutide), and Saxenda (liraglutide). Access through the NHS typically requires referral to a specialist weight management service, though private options are also available. This guide explains how each medication works, what the clinical evidence shows, and how to access them through both NHS and private routes.
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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.
Comparing UK-Licensed Weight Loss Injections
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist — meaning it activates two natural hormone pathways in the body. It's injected once weekly at doses ranging from 2.5 mg to 15 mg. Clinical trials showed participants lost an average of 15–21% of their body weight alongside diet and exercise changes.
Wegovy (semaglutide) is a GLP-1-only receptor agonist, injected once weekly at doses up to 2.4 mg. Clinical trial data showed average weight loss of around 15% of body weight. Wegovy requires a longer dose escalation period than Mounjaro — typically 17 weeks to reach the maintenance dose.
Saxenda (liraglutide) is also a GLP-1 agonist but requires once-daily injections at doses up to 3 mg, making it less convenient than the once-weekly options. Average weight loss is comparable to other GLP-1 medications.
All three work by reducing appetite, increasing feelings of fullness, and slowing gastric emptying. Individual results vary significantly, and these medications are always used alongside reduced-calorie diets and increased physical activity — not as replacements for lifestyle changes.
Clinically BackedWeight Loss
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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.
Accessing Diet Injections: NHS vs Private Routes
NHS Access: Weight loss injections are available through NHS tier 3 specialist weight management services following GP referral. NICE has approved tirzepatide (Mounjaro) for use within NHS services, though regional availability varies significantly. Waiting times for NHS specialist services can range from weeks to many months in some areas. Your GP will assess whether referral is appropriate based on your BMI and health circumstances.
Private Access: All three medications are available privately through registered online prescribing services following a clinical assessment with a UK-licensed prescriber. Private routes do not require NHS referral and offer faster access, typically within days. Costs range from £129 to £320+ monthly depending on dose and provider. Use our free BMI calculator above to understand your starting point before seeking any treatment.
Eligibility: Adults with a BMI of 30 kg/m² or above, or 27 kg/m² or above with weight-related health conditions (type 2 diabetes, high blood pressure, heart disease, sleep apnoea) may be eligible. South Asian, Chinese, Black African, and Black Caribbean adults may qualify at lower BMI thresholds due to higher metabolic health risks.
- 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 (tirzepatide) is a dual GIP+GLP-1 agonist with once-weekly dosing up to 15 mg, while Wegovy (semaglutide) is a GLP-1-only agonist also injected once weekly but up to 2.4 mg. Clinical trials suggest both produce similar average weight loss around 15–20%, though individual results vary. Choice depends on clinical suitability and prescriber assessment — there is no clear "better" option for all patients.
Can I get weight loss injections on the NHS for free?
Yes, weight loss injections are available on the NHS through specialist tier 3 weight management services. You'll need GP referral and assessment. However, availability varies greatly by region — some areas have significant waiting lists. Private options are also available if you don't want to wait for NHS referral or don't meet local NHS criteria.
How much weight will I lose with diet injections?
Clinical trials showed average weight loss of 15–21% of body weight over several months, but individual results vary significantly. Some people lose more, others less. Weight loss depends on the dose reached, adherence to the medication, dietary changes, physical activity, and personal factors like genetics and metabolism. Use our weight loss calculator to estimate potential outcomes based on current weight and dose.
Are prescription slimming injections safe?
All three UK-licensed medications have been through rigorous clinical testing and are approved by the MHRA. Common side effects include nausea, diarrhoea, and constipation, which typically improve over time. Serious side effects are rare but possible — your prescriber will assess your suitability and monitor you throughout treatment. Always discuss medical history and current medications with your prescriber.
Do I need to change my diet if I take weight loss injections?
Yes. Weight loss injections are most effective when combined with a reduced-calorie diet and increased physical activity. The medication helps reduce appetite and support feelings of fullness, but it's not a replacement for lifestyle changes. Most people find the appetite reduction makes dietary changes easier to sustain, which improves long-term outcomes.
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.