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 in the UK — What You Need to Know
If you're looking for weight loss support in the UK, prescription medications are available for eligible adults. Weight management in the UK has evolved significantly, with several clinically proven options now accessible through both NHS specialist services and private prescribing. This guide explains what's available, who qualifies, and how to find out if prescription weight loss medication might be right for you.
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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 — Your Options
Three prescription medications are currently licensed in the UK for weight management: Mounjaro (tirzepatide), a once-weekly injection that works on two hormone pathways to reduce appetite; Wegovy (semaglutide), a once-weekly GLP-1 injection; and Saxenda (liraglutide), a once-daily injection. All three are prescription-only and require clinical assessment before being prescribed.
Clinical evidence shows these medications can support meaningful weight loss when used alongside dietary changes and increased physical activity. In clinical trials, Mounjaro helped participants lose an average of 15–21% of their body weight, whilst Wegovy supported an average loss of approximately 15% of body weight — though individual results vary significantly. These are prescription weight loss injections, not cosmetic treatments, and all come with potential side effects that your prescriber will discuss with you.
- All three are GLP-1 receptor agonists or dual GIP/GLP-1 agonists
- All require a prescription following clinical assessment
- All are used alongside lifestyle changes, not instead of them
- Results vary — individual weight loss depends on many factors
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 — How to Access Weight Loss Support
Access to prescription weight management in the UK differs between NHS and private routes. NHS access is through specialist tier 3 weight management services — you'll need a referral from your GP, and availability varies by region (ICB). Waiting lists can be significant in many areas. Private access is available through online prescribing services registered with the GPhC, following a clinical assessment with a UK-licensed prescriber. Your GP can advise on NHS eligibility and waiting times in your area.
To find out if you qualify, calculate your BMI using our free BMI calculator above, then discuss your weight management goals with your GP. They can assess whether prescription medication is appropriate for you based on your individual health, medical history, and any existing conditions. Even if you don't qualify for prescription support, your GP can discuss other evidence-based weight loss approaches including dietary programmes and increased physical activity.
To find out if you qualify, calculate your BMI using our free BMI calculator above, then discuss your weight management goals with your GP. They can assess whether prescription medication is appropriate for you based on your individual health, medical history, and any existing conditions. You can also try our GLP-1 weight loss calculator to explore potential outcomes with these medications. Even if you don't qualify for prescription support, your GP can discuss other evidence-based weight loss approaches including dietary programmes and increased physical activity.
- 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.
Who is eligible for prescription weight loss medication in the UK?
Adults with a BMI of 30 or above, or 27 or above with weight-related health conditions (such as type 2 diabetes, high blood pressure, or sleep apnoea), may be eligible. South Asian, Chinese, Black African, and Black Caribbean adults may have lower BMI thresholds. Always discuss eligibility with your GP or a licensed prescriber.
What's the difference between Mounjaro and Wegovy?
Mounjaro (tirzepatide) activates two hormone pathways (GIP and GLP-1), whilst Wegovy (semaglutide) activates one (GLP-1). Mounjaro is dosed up to 15mg weekly, Wegovy up to 2.4mg weekly. Clinical trials suggest similar weight loss outcomes, though results vary individually. Your prescriber will advise which is most suitable.
How long does it take to see weight loss results?
Weight loss typically begins within the first 4–8 weeks of starting treatment. Most significant results are seen over 12–16 weeks as doses are increased. Results continue over months of treatment. Combined with reduced-calorie diet and increased physical activity, sustainable weight loss usually follows. Individual timelines vary.
Can I get weight loss injections on the NHS?
Yes, NICE has approved tirzepatide (Mounjaro) and semaglutide (Wegovy) for NHS use through specialist tier 3 weight management services. You'll need a GP referral, and availability varies significantly by region. Waiting lists can be lengthy in many areas. Check with your local NHS weight management service.
What are the main side effects of weight loss injections?
Common side effects include nausea, diarrhoea, constipation, and stomach discomfort — most commonly in the first few weeks as your body adjusts. These often improve over time. Serious side effects are rare but can include pancreatitis symptoms (severe stomach pain). Always report persistent symptoms to your prescriber.
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.