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 Comparison UK — Your Guide to Prescription Options
If you're exploring weight management UK options, prescription injections may help alongside diet and exercise. Three GLP-1 medications are currently licensed in the UK: Mounjaro (tirzepatide), Wegovy (semaglutide), and Saxenda (liraglutide). Each works differently, costs differently, and is accessed differently through the NHS or private prescribing. This guide compares all three to help you understand which might be suitable and how to discuss them with your GP.
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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 — What You Need to Know
Mounjaro (tirzepatide) is a once-weekly injection that activates two hormone pathways (GIP and GLP-1). Clinical trials showed average weight loss of around 15–21% of body weight over 72 weeks — though individual results vary significantly. It starts at 2.5 mg and increases to a maximum of 15 mg weekly.
Wegovy (semaglutide) is also once-weekly, activating the GLP-1 pathway alone. STEP trial data showed approximately 15% average weight loss at the maximum 2.4 mg dose. It starts at 0.25 mg and escalates over 16 weeks.
Saxenda (liraglutide) is a daily injection with a maximum dose of 3 mg per day. It is the longest-established of the three in the UK. Average weight loss is typically 5–10% of body weight — generally less than once-weekly alternatives.
All three are prescription-only medicines and require clinical assessment before being prescribed. None is a "clinically supported injection" — they work best alongside a reduced-calorie diet and increased physical activity. Try our free GLP-1 weight loss calculator to estimate potential outcomes at different doses.
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.
NHS Access vs Private Prescribing — How to Get Started
NHS route: Ask your GP for a referral to a specialist weight management service (tier 3 or 4). Eligibility typically requires a BMI of 30 or above, or 27–29.9 with weight-related health conditions such as type 2 diabetes, high blood pressure, or sleep apnoea. NHS access is free but availability and waiting times vary significantly by region — some areas have waits of several months to over a year.
Private route: Online consultations with UK-licensed prescribers through GPhC-registered pharmacies offer faster access (often within days). You'll be assessed for clinical suitability and charged approximately £129–£320 per month depending on dose and provider.
Use our free BMI calculator above to check your starting point, then discuss weight management UK options with your GP. They can advise you on NHS eligibility and referral, or discuss private options if you prefer faster access.
- 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, Wegovy, and Saxenda?
Mounjaro (tirzepatide) activates two hormone pathways and is once-weekly; Wegovy (semaglutide) activates one pathway, also once-weekly, with slightly lower average weight loss; Saxenda (liraglutide) is a daily injection with the lowest average weight loss of the three. All are prescription-only and require clinical assessment. Individual results vary.
How much weight can I expect to lose?
Clinical trials show Mounjaro at 15–21%, Wegovy at around 15%, and Saxenda at 5–10% average weight loss. These are averages — individual results depend on dose, adherence, diet, exercise, genetics, and other factors. Your GP or prescriber can discuss realistic expectations for your situation.
Can I get weight loss injections on the NHS?
Yes, through specialist tier 3/4 weight management services. You'll need a GP referral and typically a BMI of 30 or above, or 27–29.9 with weight-related health conditions. Availability and waiting times vary by region. Private prescribing offers faster access but at a cost.
Are weight loss injections safe?
All three are licensed medicines with established safety profiles when used as prescribed. Common side effects include nausea, diarrhoea, and constipation — usually mild and temporary. Serious side effects are rare but possible. Your prescriber will assess whether any is suitable for you based on your health history.
Do I need to change my diet and exercise if I use these injections?
Yes. Weight loss injections work best alongside a reduced-calorie diet and increased physical activity. They support appetite control and feeling fuller after meals, but they are not substitutes for lifestyle changes. Track your progress using our free progress tracker alongside any medication you're prescribed.
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.