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 Loss Medication Options Available in the UK
If you're exploring weight management in the UK, prescription medication may be an option if you meet certain eligibility criteria. The NHS and private prescribers offer several evidence-based weight loss medications for adults with obesity or overweight with weight-related health conditions. This guide explains what's available, how these medications work, who can access them, and how to find out if you're eligible. Weight management works best alongside dietary changes and increased physical activity.
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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.
UK-Licensed Weight Loss Medications Explained
Three prescription-only medicines are currently licensed in the UK for weight management in adults:
- Mounjaro (tirzepatide) — a dual GIP and GLP-1 receptor agonist injected once weekly. Clinical trials showed participants lost an average of 15–21% of their body weight over 72 weeks, though individual results vary significantly.
- Wegovy (semaglutide) — a GLP-1 receptor agonist injected once weekly. In clinical trials, it helped participants lose approximately 15% of their body weight on average, alongside a reduced-calorie diet and increased physical activity.
- Saxenda (liraglutide) — a GLP-1 receptor agonist given as a daily injection. It is also licensed for weight management but is less commonly prescribed than the weekly injections.
All three work by affecting hormones that regulate appetite and fullness. Eligibility typically requires a BMI of 30 or above, or 27 or above with weight-related health conditions such as type 2 diabetes, high blood pressure, or cardiovascular disease. Use our free BMI calculator above to check where you currently fall on the BMI scale.
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.
Accessing Weight Loss Medication: NHS and Private Routes
NHS access: Weight loss medications are available through specialist tier 3 and tier 4 weight management services. You'll typically need a GP referral, and availability varies significantly by region. Waiting lists can be lengthy in many areas. Your GP can advise whether you meet eligibility criteria and how to access local services.
Private access: GPhC-registered online pharmacies offer prescription weight loss medication following an online clinical assessment with a UK-licensed prescriber. This route does not require NHS referral and medicines may be available more quickly, though costs apply. Whether you choose NHS or private, a clinical assessment is essential to ensure the medication is safe and appropriate for your individual health profile. Our GLP-1 weight loss calculator can help you understand potential outcomes at different doses.
- 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 Mounjaro and Wegovy?
Mounjaro (tirzepatide) is a dual GIP and GLP-1 agonist, while Wegovy (semaglutide) is a GLP-1 agonist only. Mounjaro showed slightly higher average weight loss in clinical trials (15–21% vs 15%), but individual results vary. Both are injected once weekly. A prescriber will assess which is more suitable for you.
Who is eligible for prescription weight loss medication in the UK?
Generally, adults with a BMI of 30 or above, or 27 or above with weight-related health conditions (type 2 diabetes, high blood pressure, cardiovascular disease, sleep apnoea), may be eligible. Your GP or a licensed prescriber will assess your individual circumstances and medical history.
How quickly will I lose weight on these medications?
Weight loss varies considerably between individuals. Clinical trials showed average losses of 15–21% of body weight over several months, but some people lose less and some lose more. Weight loss is most effective alongside a reduced-calorie diet and increased physical activity. Use our weight converter to track changes between kg and stone as you progress.
Can I get weight loss medication through the NHS?
Yes, prescription weight loss medicines are available through NHS specialist weight management services (tier 3 and 4). You'll typically need a GP referral. Availability and waiting times vary significantly by region. Contact your GP to discuss eligibility and local provision.
What are the main side effects of weight loss injections?
Common side effects include nausea, diarrhoea, constipation, and stomach pain, especially when starting or increasing doses. These often improve over time. Serious side effects are rare but can include pancreatitis (severe stomach pain) or gallbladder problems. Always discuss potential side effects with your prescriber before starting.
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.