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
Which Is The Best Weight Loss Injection For You?
There's no single "best" weight loss injection — the right choice depends on your individual health, preferences, and NHS or private access. Three prescription-only medications are currently licensed for weight management in the UK: Mounjaro (tirzepatide), Wegovy (semaglutide), and Saxenda (liraglutide). Each works differently, has different dosing schedules, and may suit different people. This guide compares them to help you understand your options and what to discuss with your GP or prescriber.
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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.
How The Three Weight Loss Injections Work
The three UK-licensed weight loss injections work through different mechanisms, which is why results and side effects vary between individuals.
- Mounjaro (tirzepatide) activates two hormone pathways — GIP and GLP-1 — making it a dual receptor agonist. Clinical trials showed Mounjaro helped participants lose an average of 15–21% of their body weight over 72 weeks, alongside reduced-calorie diet and increased physical activity. It's administered once weekly.
- Wegovy (semaglutide) activates the GLP-1 pathway only. The STEP-1 trial showed average weight loss of approximately 14.9% of body weight at 68 weeks. Also once weekly.
- Saxenda (liraglutide) is also a GLP-1 agonist but requires a daily injection rather than weekly. Average weight loss in trials was approximately 5–8% of body weight.
Important: Individual results vary significantly. These medications work best when combined with a reduced-calorie diet and increased physical activity. Try our GLP-1 weight loss calculator to see projected results 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.
How To Access Weight Loss Injections In The UK
Access depends on whether you pursue NHS or private routes. NHS access: Prescription weight loss medication is available through specialist tier 3 weight management services, which require a GP referral. However, NHS availability is very limited and varies significantly by region — waiting lists can be several months or longer in many areas.
Private access: All three medications are available through GPhC-registered online pharmacies following an online clinical assessment with a UK-licensed prescriber. This route does not require NHS referral and can be faster, though you will need to pay for treatment privately. A prescriber will assess whether prescription weight loss medication is suitable for your health before issuing a 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.
Is one weight loss injection better than the others?
No single injection is "best" for everyone. Mounjaro shows slightly higher average weight loss in clinical trials (15–21%) compared to Wegovy (14.9%), but individual results vary. The "best" choice depends on your health profile, injection preference (weekly vs daily), side effect tolerance, and access. Your prescriber will advise based on your individual circumstances.
Can I use my BMI to check if I'm eligible for weight loss injections?
Yes, in part. UK eligibility criteria include: BMI of 30 or above, or BMI of 27–29 with weight-related health conditions like type 2 diabetes or high blood pressure. Use our free BMI calculator to check your BMI, then discuss eligibility with your GP or prescriber. Ethnicity-adjusted thresholds apply for some populations.
Which injection has the fewest side effects?
All three can cause nausea, diarrhoea, vomiting, and constipation — these are very common. Saxenda, being a lower-dose GLP-1 agonist given daily, may cause fewer severe side effects for some people, but this varies. Your prescriber can help assess which medication might suit your tolerability profile.
Will the NHS pay for weight loss injections?
The NHS does prescribe weight loss medications, but access is limited and prioritised for severe obesity (BMI ≥35 or ≥30 with complications) and is managed through specialist weight management services. Waiting times and availability vary significantly by region. Discuss with your GP about local NHS options.
What's the difference between Ozempic and Wegovy?
Both contain semaglutide, but Ozempic (up to 2 mg) is licensed for type 2 diabetes management, not weight loss. Wegovy (up to 2.4 mg) is the licensed weight management version. Using Ozempic for weight loss would be off-label use. Always use the medication licensed for the intended purpose.
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.