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
Weight Loss Medication Options in the UK
If you've seen weight loss discussed on television or social media and wondered about your own options, you're not alone. Several prescription weight management medications are now available in the UK for eligible adults. These work through different mechanisms to help support sustainable weight loss alongside diet and exercise. Understanding what's available, who qualifies, and how to access these treatments can help you have an informed conversation with your GP or a healthcare professional about whether prescription weight loss medication might be right for you.
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 Prescription Weight Loss Medications
Three prescription medications are currently licensed for weight management in the UK: Mounjaro (tirzepatide), Wegovy (semaglutide), and Saxenda (liraglutide). Mounjaro and Wegovy are once-weekly injections, whilst Saxenda is a daily injection.
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist. In clinical trials, participants taking 15 mg once weekly lost an average of approximately 21% of their body weight over 72 weeks, alongside a reduced-calorie diet and increased physical activity.
Wegovy (semaglutide) is a GLP-1 receptor agonist. In clinical trials, participants taking the 2.4 mg maintenance dose lost an average of approximately 15% of body weight over 68 weeks with lifestyle changes.
Both medications work by affecting how your body regulates appetite, helping you feel fuller and reducing food cravings. Individual results vary significantly, and these medications are prescribed only following a clinical assessment by a licensed prescriber.
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.
Eligibility and How to Access Treatment in the UK
To be eligible for prescription weight loss treatment in the UK, you typically need a BMI of 30 or above, or a BMI of 27–29.9 with at least one weight-related health condition (such as type 2 diabetes, high blood pressure, or sleep apnoea). Adults of South Asian, Chinese, Black African, or Black Caribbean heritage may have lower eligibility thresholds due to higher health risks at lower BMI levels.
NHS access is through specialist tier 3 weight management services, usually requiring a referral from your GP. Waiting times vary by region and can be lengthy. Private access is available through licensed online prescribers following a clinical assessment, without NHS referral. Your GP can advise on both routes and help you understand which option suits your circumstances.
Check your personal BMI using our free BMI calculator above to understand whether you might fall within the eligible range. Use our GLP-1 weight loss calculator to see projected weight loss outcomes at different doses, helping you explore what realistic expectations might look like. Neither calculator replaces a clinical assessment — your prescriber will make an individual evaluation based on your full health picture.
- 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) is a dual GIP+GLP-1 agonist whilst Wegovy (semaglutide) is a GLP-1 agonist only. Clinical trials showed Mounjaro achieved slightly higher average weight loss (approximately 21% vs 15%), but individual results vary. Both require prescription and clinical assessment.
Can I get prescription weight loss medication on the NHS?
Yes, but access is through specialist tier 3 weight management services, usually via referral from your GP. Availability and waiting times vary significantly by region and ICB. Your GP can discuss NHS options and eligibility with you, or recommend private alternatives if NHS waiting lists are lengthy in your area.
How quickly will I lose weight on these medications?
Clinical trials showed average weight loss over 68–72 weeks. However, individual results vary considerably based on dose, adherence, diet, exercise, genetics, and other factors. A prescriber will discuss realistic timescales during your assessment. MyWeightCheck's GLP-1 calculator can help illustrate potential ranges, but it's not a assures.
Are there side effects with prescription weight loss injections?
Yes. Common side effects include nausea, diarrhoea, constipation, and stomach discomfort, particularly when starting or increasing doses. Most improve over time. Serious side effects are rare but can include pancreatitis symptoms. Your prescriber will discuss the full risk-benefit profile during your assessment.
What if I don't qualify for prescription weight loss medication?
If you don't meet BMI or health condition criteria, sustainable weight loss through diet and exercise remains the evidence-based approach. NHS Tier 1 and 2 services offer free support including digital tools, behaviour change programmes, and community weight management groups. Your GP can refer you to these resources.
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.