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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How Much Are Slimming Injections in the UK?
Slimming injections—including Mounjaro, Wegovy, and Saxenda—are prescription-only weight loss medications available through NHS specialist services or private prescription pathways in the UK. All three are GLP-1 receptor agonists (or in Mounjaro's case, a dual GLP-1 and GIP agonist) that help support weight management alongside diet and exercise. Costs, availability, and mechanisms differ significantly between options, and eligibility depends on your BMI and health profile. This guide compares all three UK-licensed weight loss injections to help you understand your options.
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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.
Three UK-Licensed Weight Loss Injections: How They Compare
The three prescription slimming injections licensed in the UK are Mounjaro (tirzepatide), Wegovy (semaglutide), and Saxenda (liraglutide). All are GLP-1 weight loss injections designed to reduce appetite and support feeling fuller after meals.
- Mounjaro: Dual GIP and GLP-1 agonist; once-weekly injection; doses range from 2.5 mg to 15 mg; clinical trials showed average weight loss of 15–21% body weight over 72 weeks alongside reduced-calorie diet and exercise.
- Wegovy: GLP-1 agonist only; once-weekly injection; doses from 0.25 mg to 2.4 mg; clinical trials demonstrated average weight loss around 15% body weight.
- Saxenda: GLP-1 agonist; once-daily injection; doses from 0.6 mg to 3 mg; older licensed option with established safety data.
Each works through similar appetite-suppressing mechanisms but with different dosing schedules. Our free GLP-1 weight loss calculator can help you estimate potential weight loss projections at different doses. Individual results vary significantly, and all are prescription-only medications requiring clinical assessment before use.
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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
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NHS vs Private Access: How to Get Slimming Injections in the UK
NHS access: Weight loss injections are available through NHS tier 3 specialist weight management services, but you must be referred by your GP and meet eligibility criteria (BMI ≥30, or BMI 27–29.9 with weight-related health conditions). Availability varies by region, and waiting lists can be lengthy.
Private access: Available through GPhC-registered online prescribing services following an online clinical assessment with a UK-licensed prescriber. No NHS referral needed. Costs typically range from £129–£320 monthly depending on dose and provider.
Eligibility for both: Adults aged 18+ with BMI ≥30, or 27–29.9 with conditions like type 2 diabetes, hypertension, or sleep apnoea. Use our free BMI calculator to check your current BMI and healthy weight range. Your GP or prescriber will assess whether prescription slimming injections are appropriate for you.
- 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 and Wegovy?
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist with a once-weekly injection up to 15 mg; Wegovy (semaglutide) is GLP-1 only with a once-weekly injection up to 2.4 mg. Clinical trial data showed similar average weight loss (15–21% for Mounjaro, ~15% for Wegovy), but individual results vary. Your prescriber will recommend the most suitable option based on your health profile.
Can I get slimming injections on the NHS for free?
Yes, if you meet eligibility criteria and are referred to an NHS tier 3 specialist weight management service by your GP. However, NHS availability varies significantly by region and waiting times can be substantial. Private prescription services offer faster access but involve out-of-pocket costs.
Are all slimming injections prescription-only?
Yes. Mounjaro, Wegovy, and Saxenda are all prescription-only medicines in the UK. They can only be obtained following a clinical assessment by a licensed prescriber (either NHS or private). Never purchase weight loss injections without a prescription—unregulated products carry serious health risks.
How often do I inject slimming injections?
Mounjaro and Wegovy are both once-weekly injections. Saxenda is injected once daily. Your prescriber will advise on injection technique and site rotation. All are self-administered at home using pre-filled pens.
What results can I expect from slimming injections?
Clinical trials showed average weight loss of 15–21% of body weight over 72 weeks with Mounjaro, and around 15% with Wegovy—achieved alongside a reduced-calorie diet and increased physical activity. Individual results vary significantly. Weight loss injections are most effective as part of a comprehensive approach including lifestyle changes, not as a standalone 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.