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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Diet Injection Options Available in the UK
If you're considering a diet injection for weight management, you'll find three main prescription options available in the UK: Mounjaro (tirzepatide), Wegovy (semaglutide), and Saxenda (liraglutide). These are all licensed weight loss injections prescribed to adults who meet specific eligibility criteria. Each works differently, requires a prescription following clinical assessment, and can be accessed either through the NHS or privately. Understanding your options helps you make an informed decision with your GP or prescriber about which might be right for your health needs.
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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 — How They Compare
Three prescription weight loss injections are currently licensed in the UK. Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist — a newer mechanism that activates two hormone pathways to regulate appetite and food intake. Clinical trials showed participants lost an average of 15–21% of their body weight at different doses. Wegovy (semaglutide) is a GLP-1 receptor agonist administered once weekly, with clinical evidence showing approximately 14.9% average weight loss over 68 weeks. Saxenda (liraglutide) is also a GLP-1 medication but requires daily injections rather than weekly, with similar weight loss outcomes.
- Mounjaro: 2.5–15 mg, once weekly
- Wegovy: 0.25–2.4 mg, once weekly
- Saxenda: 0.6–3 mg, once daily
All three are prescription-only medicines. Individual results vary significantly, and each medication is most effective when combined with a reduced-calorie diet and increased physical activity. Use our free GLP-1 weight loss calculator above to explore potential outcomes at different dose levels.
Clinically BackedWeight Loss
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 and Private Access — Eligibility and How to Get a Diet Injection
In the UK, weight loss injection eligibility requires a BMI of 30 or above, or 27–29.9 with weight-related health conditions (high blood pressure, type 2 diabetes, cardiovascular disease, or sleep apnoea). NHS access is through specialist tier 3/4 weight management services — referral from your GP is required, and availability varies significantly by region with potentially long waiting lists. Private access is available through GPhC-registered online pharmacies following an online clinical assessment with a UK-licensed prescriber; no NHS referral is needed. Costs range from approximately £129–£320 monthly depending on the medication and dose. Either route requires a proper clinical assessment to confirm suitability before prescription.
- 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 is a dual GIP and GLP-1 agonist (newest mechanism), while Wegovy and Saxenda are both GLP-1 agonists. Mounjaro and Wegovy are once-weekly injections; Saxenda is daily. Clinical trials showed similar weight loss outcomes overall, though individual results vary. Your prescriber can advise which suits your health profile.
Can I get a diet injection through the NHS?
Yes, but access is through specialist weight management services (tier 3/4), not routine GP prescribing. You need a referral from your GP, and eligibility requires a BMI of 30+ or 27–29.9 with weight-related health conditions. Regional availability varies significantly with waiting lists in many areas.
What are the main side effects of weight loss injections?
Common side effects include nausea, diarrhoea, constipation, and stomach pain — typically mild and transient. More serious but rare effects include pancreatitis (severe abdominal pain) and gallbladder problems. Always discuss side effects with your prescriber and seek urgent medical attention for severe symptoms.
How much weight can I expect to lose with a diet injection?
Clinical trials show average weight loss of 14.9–21% of body weight depending on the medication and dose. However, individual results vary considerably. Weight loss occurs alongside diet and exercise changes, not as a standalone treatment. Use our free weight loss calculator to explore realistic projections based on clinical data.
Do I need to change my diet and exercise when taking a diet injection?
Yes. These medications are most effective when combined with a reduced-calorie diet and increased physical activity. A prescriber will discuss lifestyle changes as part of your treatment plan. Weight loss injections support your efforts but are not a replacement for healthy habits.
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.