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
Compare Weight Loss Medication Available in the UK
If you're exploring weight management UK options, prescription medications are now available for eligible adults through both NHS and private routes. This guide compares the three main prescription weight loss medicines licensed in the UK—Mounjaro, Wegovy, and Saxenda—so you can understand the differences, expected results, and how to find out if you qualify. Whether you're interested in GLP-1 weight loss medication or want to know about NHS options, we'll help you make an informed decision with your GP.
10,000+ calculations today · NHS-aligned thresholds · 100% free
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 Compared
Three prescription medications are currently licensed for weight management in the UK: Mounjaro (tirzepatide), Wegovy (semaglutide), and Saxenda (liraglutide). Mounjaro is a dual GIP and GLP-1 receptor agonist, while Wegovy and Saxenda are GLP-1 receptor agonists only. In clinical trials, Mounjaro helped participants lose an average of 15–21% body weight, Wegovy approximately 15%, and Saxenda around 5–10% depending on the dose. Mounjaro and Wegovy are both once-weekly injections, while Saxenda requires a daily injection. All three work by reducing appetite, increasing feelings of fullness, and slowing digestion. Individual results vary significantly, and all are most effective alongside a reduced-calorie diet and increased physical activity. Use our free BMI calculator above to check your current BMI and understand whether you might be eligible for prescription weight loss support.
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.
NHS vs Private Access and Eligibility
In the UK, prescription weight loss medication is available through NHS specialist weight management services (tier 3) or via private consultation with a licensed prescriber. NHS access typically requires a GP referral and assessment through your local integrated care board—though availability and waiting times vary significantly by region. Private access is faster, available without an NHS referral, and can be arranged through registered online healthcare providers following a clinical assessment. Eligibility is similar across both routes: adults with a BMI of 30 or above, or BMI of 27–29.9 with weight-related health conditions such as type 2 diabetes, high blood pressure, or sleep apnoea. Your GP can discuss which route and medication might suit your situation. Track your progress with our free progress tracker once you begin any weight management programme.
- 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 Mounjaro and Wegovy?
Both are once-weekly injections for weight management, but Mounjaro (tirzepatide) acts on two hormone pathways (GIP and GLP-1), whilst Wegovy (semaglutide) targets GLP-1 only. Clinical trials suggest Mounjaro may produce slightly greater average weight loss (15–21% vs approximately 15%), though individual results vary. Both require a prescription and clinical assessment.
Can I get weight loss injections on the NHS?
Yes. NICE has approved tirzepatide and semaglutide for use within NHS specialist weight management services (tier 3). Access requires a GP referral and assessment by a specialist team. Waiting times and availability vary by region. Private prescription is an alternative if NHS waiting times are long in your area.
Who is eligible for prescription weight loss medication in the UK?
You may be eligible if you have a BMI of 30 or above, or BMI of 27–29.9 with weight-related health conditions (type 2 diabetes, hypertension, sleep apnoea, or cardiovascular disease). For adults of South Asian, Chinese, Black African, or Black Caribbean heritage, lower BMI thresholds may apply. A GP or licensed prescriber will assess individual suitability.
How much weight can I expect to lose with these medications?
Clinical trial averages show Mounjaro: 15–21% body weight, Wegovy: approximately 15%, and Saxenda: 5–10%. However, results vary significantly between individuals. Weight loss is greatest when medication is combined with a reduced-calorie diet and physical activity. Our GLP-1 weight loss calculator can help you estimate potential outcomes at different doses.
Are there side effects I should know about?
Common side effects include nausea, diarrhoea, constipation, and stomach pain—typically worse when starting and often improve over time. Serious side effects are rare but can include pancreatitis. A prescriber will discuss full risks during your clinical assessment and monitor you throughout treatment.
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.