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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The Best Weight Loss Injections Available in the UK
If you're exploring weight management options in the UK, prescription weight loss injections may be worth considering. Three medications are currently licensed for weight management: Mounjaro (tirzepatide), Wegovy (semaglutide), and Saxenda (liraglutide). All are prescription-only and require a clinical assessment. This guide explains how these injections work, who is eligible, and how to access them through the NHS or privately. Use our free BMI calculator above to check whether you may be eligible for prescription weight management support.
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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.
UK-Licensed Weight Loss Injections Explained
Mounjaro (tirzepatide) is a once-weekly injection that activates two natural hormone pathways — GIP and GLP-1 — to help regulate appetite and reduce food cravings. In clinical trials, participants lost an average of 15–21% of their body weight over 72 weeks, alongside a reduced-calorie diet and increased physical activity. Individual results vary significantly.
Wegovy (semaglutide) is another once-weekly injection that works via the GLP-1 pathway alone. Clinical trials showed average weight loss of around 15% of body weight at the maximum dose, again combined with lifestyle changes.
Saxenda (liraglutide) is a daily injection (not weekly) that also targets GLP-1. It may help with weight management but requires daily injections rather than weekly ones.
All three are prescription-only medicines. Common side effects include nausea, diarrhoea, and constipation — typically mild and often improve over time. Eligibility is assessed on an individual basis by a 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 How to Access Weight Loss Injections
In the UK, adults may be eligible for prescription weight loss injections 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, high blood pressure, or cardiovascular disease. For people of South Asian, Chinese, Black African, or Black Caribbean heritage, lower BMI thresholds apply.
NHS access: Referral to a tier 3 specialist weight management service through your GP. Availability varies by region and waiting times can be lengthy.
Private access: Available through GPhC-registered online pharmacies following an online clinical assessment. No GP referral needed. Use our free GLP-1 weight loss calculator to explore potential weight loss projections 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.
What makes Mounjaro different from Wegovy?
Mounjaro (tirzepatide) is a dual GIP and GLP-1 agonist, meaning it activates two hormone pathways. Wegovy (semaglutide) activates only the GLP-1 pathway. Clinical trials suggest Mounjaro may result in slightly higher average weight loss, though individual results vary. Both are once-weekly injections.
Can I get weight loss injections on the NHS?
Yes, if you are eligible. You'll need to be referred to a specialist weight management service (tier 3) by your GP. Eligibility depends on BMI and health conditions. However, NHS waiting times vary significantly by region — in many areas, there are substantial waiting lists.
Are weight loss injections safe?
Weight loss injections are prescription-only medicines with safety data from large clinical trials. Common side effects like nausea usually improve over time. However, they are not suitable for everyone — pregnant women, people with certain medical conditions, and those on specific medications cannot use them. Your prescriber will assess suitability.
How much weight will I lose with these injections?
Clinical trials show average weight loss of 15–21% of body weight over several months, depending on the medication and dose. However, individual results vary significantly. Weight loss also depends on adherence to a reduced-calorie diet and increased physical activity — injections are not a substitute for lifestyle changes.
What's the difference between NHS and private access?
NHS access requires a GP referral and assessment through a specialist weight management service — often with waiting lists. Private access is through online prescribers and GPhC-registered pharmacies, available without NHS referral, but you pay directly. Both routes require a clinical assessment before prescription.
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.