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
Medications to Help You Lose Weight in the UK
Several prescription medications are available in the UK to help with sustainable weight loss when used alongside diet and exercise. These medicines work by reducing appetite, helping you feel fuller, and supporting healthier eating habits. If you're struggling with weight management, your GP can assess whether prescription weight loss medication might be suitable for you as part of a comprehensive weight loss programme.
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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 Prescription Weight Loss Medications Work
Prescription weight loss medications in the UK fall into two main categories: GLP-1 receptor agonists and GIP/GLP-1 receptor agonists. These medicines mimic natural hormones your body produces after eating.
GLP-1 medications (Wegovy and Saxenda) work by signalling to your brain that you're satisfied with smaller portions, slowing how quickly food moves through your stomach, and supporting better blood sugar control. Mounjaro (tirzepatide) activates two hormone pathways simultaneously — GIP and GLP-1 — which may enhance appetite suppression and fat utilisation.
Clinical trials show these medications support significant weight loss alongside a reduced-calorie diet and increased physical activity. In the STEP trial, adults using Wegovy lost an average of around 15% of their body weight over 68 weeks. Results vary considerably between individuals. These are prescription-only medicines requiring assessment from a licensed prescriber to confirm suitability.
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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.
UK Eligibility and Access to Weight Loss Medications
To be prescribed weight loss medication in the UK, you typically need a BMI of 30 or above, or 27 or above if you have weight-related health conditions such as type 2 diabetes, high blood pressure, or sleep apnoea. Use our free BMI calculator to check your current BMI instantly.
Access routes differ: through the NHS via referral to specialist tier 3 weight management services (though waiting lists are lengthy in many regions), or privately through online prescribing following a clinical assessment. Your GP can advise on NHS availability in your area. Private routes often provide faster access without waiting lists, though costs vary. Whichever route you choose, a qualified prescriber must assess your individual health before any medication is prescribed.
- 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 Wegovy, Mounjaro, and Saxenda?
Wegovy (semaglutide) and Saxenda (liraglutide) are GLP-1 injections — Wegovy is once-weekly, Saxenda is daily. Mounjaro (tirzepatide) is a dual GIP/GLP-1 injection given once weekly. Clinical trials show Mounjaro may produce slightly higher average weight loss, but individual results vary significantly. All are prescription-only and require clinical assessment.
Are these the same as Ozempic?
No. Ozempic also contains semaglutide but is licensed for type 2 diabetes management only, not weight loss. Wegovy is the licensed weight loss version of semaglutide. Using Ozempic for weight loss would be off-label and not recommended. Always use the medication your prescriber has specifically prescribed for you.
How much weight can I expect to lose?
Clinical trial averages show Wegovy users lost around 15% of body weight, and Mounjaro users lost 15–21%. However, individual results vary significantly based on genetics, lifestyle changes, dose, and adherence. Use our GLP-1 weight loss calculator to explore potential outcomes at different doses alongside your specific circumstances.
Can I get prescription weight loss medication on the NHS?
Yes, through specialist tier 3 weight management services if you meet eligibility criteria. However, NHS availability varies greatly by region and waiting lists can be very long. Your GP can refer you or advise on local services. Private prescribing offers faster access if you're willing to pay.
What are the main side effects?
Common side effects include nausea, diarrhoea, constipation, and stomach pain — usually mild and temporary as your body adjusts. Serious side effects are rare but can include pancreatitis (severe stomach pain) or gallbladder problems. Always report unexpected symptoms to your prescriber. Side effect profiles are similar across all three medications, though individual experiences vary.
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.