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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Weight Reduction Medication in the UK
Weight reduction medications are prescription-only injectable medicines licensed in the UK to support weight management alongside lifestyle changes. These medications work by mimicking natural hormones that regulate appetite and food intake. If you're considering weight management support, understanding how these medications work, who's eligible, and what the evidence shows is essential. This guide covers the main options available through NHS health services and private prescribing in the UK, along with practical information to help you discuss options with your GP or a qualified healthcare professional.
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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 Weight Reduction Medications Work
The main weight reduction medications available in the UK—Wegovy (semaglutide) and Mounjaro (tirzepatide)—work by activating hormone pathways that regulate appetite and satiety. Wegovy is a GLP-1 receptor agonist, meaning it mimics glucagon-like peptide-1, a natural hormone produced in the gut that signals fullness to the brain. Mounjaro is a dual GIP and GLP-1 receptor agonist, activating two hormone pathways for potentially enhanced effects.
Both medications are once-weekly injectable medicines that also slow gastric emptying, helping you feel fuller for longer. Clinical trials have shown that alongside a reduced-calorie diet and increased physical activity, these medications may help users lose an average of 15–21% of their body weight, though individual results vary considerably. Neither medication is insulin, and both require a prescription following a clinical assessment.
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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 NHS Access
In the UK, weight reduction medications may be prescribed to adults with a BMI of 30 kg/m² or above, or a BMI of 27–29.9 with weight-related health conditions such as type 2 diabetes, high blood pressure, or sleep apnoea. For people of South Asian, Chinese, Black African, or Black Caribbean heritage, NHS guidance recommends lower BMI thresholds due to higher health risks at lower weights.
Access through the NHS typically requires referral to a specialist tier 3 weight management service—not standard GP prescription. Waiting lists vary significantly by region. Private access is available through GPhC-registered online pharmacies following an online clinical assessment. Use our free BMI calculator to check your personal BMI and explore whether you may meet eligibility criteria for prescription weight management support.
- 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 is the difference between Wegovy and Mounjaro?
Wegovy (semaglutide) is a GLP-1 receptor agonist activating one hormone pathway. Mounjaro (tirzepatide) is a dual GIP and GLP-1 agonist activating two pathways. Clinical trials show both may support similar average weight loss (15–21%), but individual results vary. Both are once-weekly injections requiring prescription and clinical assessment.
Can I get weight reduction medication through the NHS?
Yes, but access is through specialist tier 3 weight management services, not routine GP prescription. You'll need referral from your GP and assessment by the specialist service. Eligibility depends on BMI and health conditions. Waiting lists vary significantly by region. Private access is also available through online prescribing.
Are weight reduction medications safe?
Prescription weight reduction medications are licensed and have been through clinical trials. Common side effects include nausea, diarrhoea, and constipation—usually temporary. Serious side effects are rare but possible. Any prescription requires a clinical assessment to ensure suitability for you. Always discuss risks and benefits with your prescriber.
How much weight will I lose with these medications?
Clinical trials show average weight loss of 15–21% of body weight when combined with diet and exercise changes. However, individual results vary significantly—some people lose more, others less. These medications support weight loss; they don't assures specific outcomes. Your GP or prescriber can discuss realistic expectations based on your individual circumstances.
What's the difference between Ozempic and Wegovy?
Both contain semaglutide, but Ozempic is licensed for type 2 diabetes management (up to 2 mg dose) and is not approved for weight loss in the UK. Wegovy is the licensed weight management version (up to 2.4 mg). Using Ozempic for weight loss would be off-label. Always ensure you're prescribed the correct licensed medication for your treatment goal.
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.