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
NHS Weight Loss Injection — How to Access in the UK
Weight loss injections, also known as GLP-1 medications, are now available through the NHS and privately in the UK. The most commonly prescribed options are Wegovy (semaglutide) and Mounjaro (tirzepatide). These prescription-only medications may help support weight management alongside diet and physical activity. Access through the NHS is typically via specialist weight management services, though availability varies significantly by region. This guide explains how they work, who may be eligible, and your options for accessing them. Use our free BMI calculator to check whether you might qualify for weight loss medication support.
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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.
How Weight Loss Injections Work and NHS Access
Wegovy (semaglutide) and Mounjaro (tirzepatide) are the main weight loss injections available in the UK. Both are GLP-1 receptor agonists — medications that activate natural hormone pathways to help reduce appetite and support feeling fuller after meals. They work by slowing gastric emptying and sending signals to the brain that reduce food cravings.
Clinical trials showed that Wegovy helped participants lose an average of around 15% of their body weight, while Mounjaro demonstrated average weight loss of 15–21% — though individual results vary significantly and depend on dose, diet, and activity level.
NHS access: Weight loss injections are available through NHS specialist tier 3 weight management services. You need referral from your GP, and services assess eligibility based on your BMI and weight-related health conditions. Availability varies by region — some areas have long waiting lists. Private access is available through GPhC-registered online pharmacies following an online clinical assessment and prescription from a UK-licensed prescriber.
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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.
Eligibility and What to Expect
You may be eligible for NHS weight loss injection treatment if you have a BMI of 30 or above, or a BMI of 27–29.9 with at least one weight-related health condition such as type 2 diabetes, prediabetes, high blood pressure, or sleep apnoea. Lower BMI thresholds apply for people of South Asian, Chinese, Black African, or Black Caribbean heritage due to higher health risks at lower weights.
Treatment involves once-weekly injections starting at a low dose, gradually increasing over several weeks. Common side effects include nausea, constipation, diarrhoea, and stomach discomfort — usually mild and improving over time. Weight loss medication works best alongside a reduced-calorie diet and increased physical activity. Track your progress with our free progress tracker, and use our GLP-1 weight loss calculator to estimate potential outcomes at different doses.
- 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.
Can I get weight loss injections free on the NHS?
Yes, Wegovy and Mounjaro are available through NHS specialist weight management services if you meet eligibility criteria. However, availability varies significantly by region and waiting times can be lengthy. Your GP can refer you to your local tier 3 weight management service. If NHS access is limited in your area, private prescription is available through online pharmacies.
What's the difference between Wegovy and Mounjaro for weight loss?
Wegovy (semaglutide) is a GLP-1 receptor agonist. Mounjaro (tirzepatide) is a dual GIP and GLP-1 agonist, activating two hormone pathways. Clinical trials showed Mounjaro may produce slightly higher average weight loss (15–21%) compared to Wegovy (around 15%), but individual results vary. Both require prescription and clinical assessment.
How much weight can I lose with NHS weight loss injections?
Clinical trial data showed average weight loss of 15–21% of body weight depending on medication and dose, alongside diet and activity changes. However, results vary significantly between individuals. Some people lose more, some lose less. Use our BMI calculator and GLP-1 weight loss calculator to understand your personal context and potential ranges.
Are weight loss injections safe and what are the side effects?
Prescription weight loss injections are licensed medicines with established safety profiles from clinical trials. Common side effects include nausea, constipation, diarrhoea, and stomach discomfort — usually mild and reducing over time. Serious side effects are rare but can include pancreatitis or gallbladder issues. Always discuss risks with your prescriber before starting.
How do I get a weight loss injection prescription in the UK?
For NHS access, ask your GP for referral to your local tier 3 specialist weight management service — eligibility is assessed there. For private prescription, book an online consultation with a UK-licensed prescriber through a GPhC-registered pharmacy. Both routes require clinical assessment to confirm the medication is appropriate for you.
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.