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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UK Weight Loss Injections: What You Need to Know
Weight loss injections are prescription-only medications now available in the UK to help adults manage their weight alongside diet and exercise. If you're interested in weight management options in the UK, prescription injections like Mounjaro and Wegovy may be suitable depending on your BMI and health circumstances. This guide explains the licensed options available, who is eligible, and how to access them through the NHS or privately. Use our free BMI calculator above to check your current BMI and see where you stand against NHS eligibility thresholds.
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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.
UK-Licensed Weight Loss Injections Available Now
Three prescription weight loss injections are currently licensed in the UK for weight management:
- Mounjaro (tirzepatide) — a dual GIP and GLP-1 receptor agonist, dosed from 2.5 mg to 15 mg once weekly. Clinical trials showed an average weight loss of 15–21% body weight over 72 weeks when combined with reduced-calorie diet and increased physical activity.
- Wegovy (semaglutide) — a GLP-1 receptor agonist, dosed up to 2.4 mg once weekly. STEP trial data showed an average weight loss of around 15% body weight at the maximum dose.
- Saxenda (liraglutide) — a GLP-1 receptor agonist, given as a daily injection up to 3 mg. This was the first GLP-1 injection approved in the UK for weight management.
All three are prescription-only medicines that work by helping to regulate appetite, support feeling fuller after meals, and slow how quickly food leaves the stomach. Individual results vary significantly, and these medications are used alongside lifestyle changes, not instead of them. Try our GLP-1 weight loss calculator to explore potential outcomes at different doses.
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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.
NHS vs Private Access: How to Get a UK Weight Loss Injection
NHS access: Weight loss injections are available through NHS specialist tier 3 weight management services, but you must be referred by your GP. NICE has approved tirzepatide (Mounjaro) for NHS use, though availability varies significantly by region and waiting lists can be substantial in many areas.
Private access: You can obtain a prescription privately through a UK-licensed prescriber via online consultation without an NHS referral. This typically provides faster access but involves a private cost.
To find out if you're eligible, start by speaking to your GP about your weight management goals. They can assess your BMI, health history, and any weight-related conditions to determine suitability. Use the weight converter on this page to check your weight in different units if needed.
- 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 BMI do I need to qualify for a UK weight loss injection?
You may be eligible if you have a BMI of 30 or above, or 27–29.9 with at least one weight-related health condition (such as type 2 diabetes, high blood pressure, or sleep apnoea). For adults of South Asian, Chinese, Black African, or Black Caribbean heritage, lower thresholds may apply. Use our free BMI calculator above to check your current BMI.
How much weight can I expect to lose with a UK weight loss injection?
Clinical trials show average weight loss of 15–21% body weight over 72 weeks, depending on the medication and dose. However, individual results vary considerably. These medications work best alongside a reduced-calorie diet and increased physical activity — they are not a substitute for lifestyle changes.
Are weight loss injections available on the NHS in the UK?
Yes, Mounjaro, Wegovy, and Saxenda are all available through NHS specialist weight management services, but you must be referred by your GP. Availability and waiting times vary by region. Private prescriptions are also available without NHS referral.
What are the side effects of UK weight loss injections?
Common side effects include nausea, diarrhoea, vomiting, constipation, and abdominal pain, particularly during the first few weeks. Most side effects are mild and tend to improve over time. Serious side effects are rare but can include pancreatitis. Always discuss potential side effects with your prescriber.
Can I switch between Mounjaro and Wegovy in the UK?
Switching between medications must be managed by your prescriber. While approximate dose equivalences exist, there is no official conversion chart. Your prescriber will advise on the appropriate approach based on your individual circumstances and response to treatment.
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.