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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Weight Loss Injections in the UK — What You Need to Know
Weight loss injections are prescription-only medicines that may help adults manage excess weight alongside lifestyle changes. In the UK, three medications are licensed for weight management: tirzepatide (Mounjaro), semaglutide (Wegovy), and liraglutide (Saxenda). These are not cosmetic treatments but clinical interventions assessed by healthcare professionals. Access is available through NHS specialist weight management services or private prescribing following clinical assessment. This guide explains how they work, who may be eligible, and what to expect.
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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 UK Eligibility
Weight loss injections approved in the UK are GLP-1 receptor agonists (or dual GIP/GLP-1 agonists in the case of Mounjaro). These medications mimic natural gut hormones that regulate appetite and blood sugar. They work by signalling fullness to the brain, reducing food cravings, and slowing digestion—supporting a smaller appetite without relying on willpower alone.
In the UK, you may be eligible for prescription weight loss medication if you have a BMI of 30 or above, or a BMI of 27–29.9 with weight-related health conditions such as type 2 diabetes, high blood pressure, or sleep apnoea. Adults of South Asian, Chinese, Black African, or Black Caribbean heritage may qualify at lower BMI thresholds due to higher health risks at those levels. Use our free BMI calculator to check where you fall, then discuss options with your GP or a licensed prescriber.
Weight loss injections are prescribed through NHS specialist services (tier 3/4 weight management) or private online prescribing. Availability varies by region; NHS waiting lists can be lengthy in some areas.
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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.
Weight Loss Injection Options and Getting Started in the UK
Three medications are currently licensed for weight management in the UK. Wegovy (semaglutide) is a once-weekly GLP-1 injection; clinical trials showed average weight loss of around 15% of body weight. Mounjaro (tirzepatide) is a once-weekly dual GIP/GLP-1 injection with clinical trial results showing 15–21% average weight loss at the highest dose. Saxenda (liraglutide) is a daily GLP-1 injection, less commonly prescribed now.
All require a prescription and clinical assessment. Common side effects include nausea, diarrhoea, and reduced appetite—typically mild and temporary. A prescriber will assess your health history, current medications, and suitability before prescribing. Track your progress with our free progress tracker, and use our GLP-1 weight loss calculator to estimate potential outcomes at different doses. Remember: injections work best alongside a reduced-calorie diet and increased physical activity. Individual results vary significantly.
- 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.
How much weight can you lose with weight loss injections in the UK?
Clinical trials showed average weight loss of 15–21% of body weight over 68–72 weeks, depending on the medication and dose. Individual results vary considerably. Some people lose more, others less. Weight loss injections are most effective alongside dietary changes and physical activity. Your GP or prescriber can discuss realistic expectations for your situation.
Are weight loss injections available on the NHS in the UK?
Yes, NICE has approved tirzepatide (Mounjaro) and semaglutide (Wegovy) for NHS use, but access is through specialist tier 3/4 weight management services, not standard GP prescription. Availability and waiting times vary significantly by region (ICB). Ask your GP about referral options in your area.
What are the side effects of weight loss injections?
Very common side effects include nausea, diarrhoea, constipation, vomiting, and stomach pain—usually mild and temporary as your body adjusts. Less common effects include dizziness, fatigue, headache, and injection site reactions. Serious side effects are rare but can include pancreatitis or gallbladder issues. Report severe symptoms to your GP immediately.
How do I access weight loss injections privately in the UK?
Private weight loss injections are available through GPhC-registered online pharmacies following an online clinical assessment by a UK-licensed prescriber. If prescribed, the medication is dispensed by the pharmacy. Costs typically range from £129–£320 per month depending on dose and provider.
Do weight loss injections work without diet and exercise changes?
Weight loss injections are most effective when combined with a reduced-calorie diet and increased physical activity. They support appetite control and fullness, making it easier to sustain lifestyle changes—but they are not a substitute for them. NHS guidance recommends treating injections as part of a comprehensive weight management approach.
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.