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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Drugs to Lose Weight in the UK
Several prescription medications are now available in the UK to support sustainable weight loss alongside diet and exercise. These weight loss drugs work by helping reduce appetite, increase feelings of fullness, and support healthier eating patterns. Understanding your options, how they work, and whether you're eligible is the first step toward safe, effective weight management. This guide covers prescription weight loss medications available through NHS weight management services and private prescribing in the 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 Weight Loss Drugs Work
The main prescription weight loss medications available in the UK are GLP-1 receptor agonists and dual GIP/GLP-1 agonists. These work by mimicking natural hormones produced in your gut after eating.
Wegovy (semaglutide) is a once-weekly GLP-1 injection that activates a single hormone pathway. In clinical trials (STEP-1), participants taking Wegovy lost an average of around 15% of their body weight over 68 weeks, alongside reduced-calorie diet and increased physical activity.
Mounjaro (tirzepatide) is a once-weekly injection with a dual mechanism — it activates both GIP and GLP-1 pathways. Clinical trial data (SURMOUNT-1) showed average weight loss of 15–21% of body weight, depending on dose.
Both medications are prescription-only and require a clinical assessment before being prescribed. Individual results vary significantly.
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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 How to Access Weight Loss Drugs
You may be eligible for prescription weight loss treatment in the UK if you have a BMI of 30 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. Use our free BMI calculator above to check your personal BMI.
NHS access: Referral to a specialist tier 3 weight management service through your GP. Availability and waiting times vary significantly by region.
Private access: Available through GPhC-registered online prescribing following a clinical assessment with a UK-licensed prescriber.
Our GLP-1 weight loss calculator can help you understand potential outcomes at different doses alongside lifestyle changes.
- 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 and Ozempic?
Both contain semaglutide, but Wegovy is specifically licensed for weight management (up to 2.4 mg weekly). Ozempic is licensed for type 2 diabetes (up to 2 mg) and is not approved for weight loss in the UK. Using Ozempic for weight loss would be off-label use.
How quickly will I lose weight on these drugs?
Clinical trials show average weight loss of 15–21% over 68–72 weeks, but individual results vary significantly. Most people experience gradual loss of around 0.5–1 kg weekly when combined with reduced-calorie diet and physical activity.
Are weight loss drugs safe long-term?
Both Wegovy and Mounjaro have undergone clinical trials for safety. Common side effects include nausea, diarrhoea, and vomiting, which often reduce over time. Serious side effects are rare. Your prescriber will discuss risks and benefits for your individual situation.
Can I get weight loss drugs on the NHS?
Yes, GLP-1 medications are available on the NHS through specialist tier 3 weight management services. Access requires GP referral and assessment. Availability and waiting times vary significantly by region — contact your local ICB for details.
What if weight loss drugs don't work for me?
Individual results vary — some people respond better than others. Your prescriber may adjust your dose, try a different medication, or recommend additional support. Weight loss drugs work best alongside dietary changes and physical activity, not as replacements.
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.