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
Free tracker included with every download this week
Most Effective Weight Loss Injections in the UK
If you're exploring prescription weight loss medication management uk options, injectable GLP-1 receptor agonists are among the most researched and effective tools available. These once-weekly injections work by reducing appetite, helping you feel fuller after smaller meals, and supporting sustainable weight loss alongside diet and exercise. Two main options are licensed in the UK: Wegovy (semaglutide) and Mounjaro (tirzepatide). Results vary between individuals, but clinical trials show these medications can help achieve significant weight loss when used as part of a comprehensive approach to weight management uk.
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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.
How GLP-1 Weight Loss Injections Work
GLP-1 receptor agonist medications mimic a natural hormone your gut produces after eating. They signal your brain that you're satisfied, slow how quickly food leaves your stomach, and help regulate blood sugar. This triple mechanism makes them effective for supporting nhs weight loss goals.
Wegovy (semaglutide) reaches a maximum dose of 2.4 mg once weekly. In clinical trials, participants lost an average of 15% of their body weight over 68 weeks — though individual results vary significantly. Mounjaro (tirzepatide) works differently as a dual GIP and GLP-1 agonist, activating two hormone pathways. Clinical data shows average weight loss of 15–21% depending on dose.
Both are prescription-only medicines requiring a clinical assessment from a licensed UK prescriber. They're designed to work alongside reduced-calorie diet and increased physical activity — not as standalone solutions.
- Once-weekly injections (simple to use)
- May reduce appetite and food cravings
- Evidence-based results from clinical trials
- Require prescription and assessment
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.
UK Eligibility and Access to Prescription Weight Loss
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 at least one weight-related health condition (such as type 2 diabetes, high blood pressure, or cardiovascular disease).
NHS access is through specialist tier 3 weight management services — you'll need referral from your GP, though waiting lists vary by region and can be lengthy.
Private access is available through GPhC-registered online pharmacies following an online clinical assessment — no NHS referral needed, though costs typically range from £129–£320 monthly depending on dose.
Your GP or prescriber will assess whether medication is suitable based on your medical history, current medications, and individual health factors. Use our free GLP-1 weight loss calculator above to explore potential weight loss projections at different doses, and our BMI calculator to check your starting point.
- 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.
Which weight loss injection is most effective?
Both Wegovy and Mounjaro are highly effective. Wegovy (semaglutide) showed ~15% average weight loss in clinical trials. Mounjaro (tirzepatide), as a dual-action GIP/GLP-1 agonist, showed 15–21% average weight loss. Individual results vary significantly based on dose, adherence, diet, and activity level. Your prescriber will recommend the most suitable option for you.
Are weight loss injections available on the NHS?
Yes, GLP-1 medications including Wegovy and Mounjaro are available through NHS specialist weight management services (tier 3). However, you must be referred by your GP and meet eligibility criteria (BMI ≥30, or ≥27.5 with comorbidities). Availability and waiting times vary significantly by region.
How quickly do weight loss injections work?
Most people notice appetite reduction within the first few days or weeks. Measurable weight loss typically becomes visible after 4–8 weeks of consistent use alongside diet and exercise changes. Maximum effects often take 16–20 weeks as doses are gradually increased. Patience and lifestyle changes are essential for best results.
What's the difference between Wegovy and Mounjaro?
Wegovy (semaglutide) is a single GLP-1 agonist with a maximum dose of 2.4 mg weekly. Mounjaro (tirzepatide) is a dual GIP/GLP-1 agonist with a maximum dose of 15 mg weekly. Clinical trials suggest Mounjaro may produce slightly greater average weight loss, but both are highly effective. Your prescriber will recommend based on your individual health profile.
Can I use weight loss injections without changing my diet?
Weight loss injections are designed to work alongside a reduced-calorie diet and increased physical activity — not replace these changes. Clinical trials showed weight loss when medication was combined with lifestyle modifications. For best results and long-term success, diet, exercise, and medication should work together as an integrated 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.