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
Wegovy and Mounjaro on the NHS — UK Guide
Both Wegovy (semaglutide) and Mounjaro (tirzepatide) are prescription-only weight loss injections available in the UK through NHS specialist services and private prescribing routes. This guide explains NHS eligibility criteria, how these medications differ, NICE guidance, and what to expect when accessing them through the NHS. We cover the STEP and SURMOUNT clinical trial data, UK prescribing thresholds, and the differences between tier 3 specialist services and private access routes. Use our free GLP-1 weight loss calculator to explore potential outcomes, or check your BMI using our calculator above.
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.
NHS Eligibility and NICE Guidance for Both Medications
NICE has approved both Wegovy and Mounjaro for NHS weight management, but access is through specialist tier 3 services, not standard GP prescriptions. Eligibility criteria for both medications are identical in the UK:
- BMI of 30 kg/m² or above (obesity), OR BMI of 27–29.9 kg/m² (overweight) with at least one weight-related health condition such as type 2 diabetes, prediabetes, high blood pressure, abnormal blood fats, or sleep apnoea
- For adults of South Asian, Chinese, Black African, or Black Caribbean descent, lower thresholds apply: BMI of 27.5 or above may qualify due to higher cardiovascular risk at lower weights
- Both require referral to an NHS tier 3 or tier 4 weight management service from your GP
- NHS availability varies significantly by region (ICB) — some areas have substantial waiting lists, often months to years in length
The STEP clinical trial demonstrated that semaglutide (Wegovy) achieved approximately 15% average body weight loss at 68 weeks. The SURMOUNT-1 trial showed tirzepatide (Mounjaro) achieved approximately 21% average body weight loss at 72 weeks — though individual results vary considerably alongside reduced-calorie diet and increased physical activity. Both are dual or single GLP-1 pathway activators and represent the most clinically significant weight loss medication options available on the NHS.
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 Routes in the UK
NHS access is through specialist weight management services (tier 3), typically requiring GP referral and meeting strict BMI thresholds. Waiting lists can be lengthy in most regions. Private access is available through GPhC-registered online prescribing services following a clinical assessment—no NHS referral required. Private prescriptions cost approximately £129–£320 per month depending on dose and provider. Both routes require a prescription from a UK-licensed prescriber and both involve clinical assessment of eligibility. The NHS route may be free at point of use (via NHS prescription charges or exemptions) but availability is limited and regional. Private access is faster but involves direct cost. Either route provides the same licensed medications; the choice depends on waiting times, regional availability, and personal circumstances. Track your progress with our free progress tracker once you start either medication.
- 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 Mounjaro on the NHS?
Wegovy (semaglutide) is a GLP-1 agonist; Mounjaro (tirzepatide) is a dual GIP/GLP-1 agonist. Both are approved by NICE for NHS weight management. Mounjaro showed higher average weight loss in clinical trials (~21% vs ~15%), but both are prescription-only and eligibility is identical. Individual response varies significantly.
Can I get Wegovy or Mounjaro on the NHS without a waiting list?
NHS access depends on your region and tier 3 service capacity. Many areas have substantial waiting lists. Private access via a UK prescriber is typically faster but involves direct cost. Discuss waiting times and private options with your GP—they can advise on local NHS provision.
What BMI do I need for NHS Wegovy or Mounjaro?
NHS eligibility requires BMI of 30 or above, or 27–29.9 with a weight-related health condition (type 2 diabetes, hypertension, sleep apnoea, etc.). For South Asian, Chinese, Black African, or Black Caribbean adults, lower thresholds may apply. Your GP can assess your individual eligibility.
Are there side effects I should know about with both medications?
Both cause similar side effects: nausea, diarrhoea, vomiting, constipation, and stomach pain are common initially. Most improve as your body adjusts. Serious side effects are rare but can include pancreatitis. Report severe or persistent symptoms to your GP or prescriber immediately.
How long does it take to see weight loss results on the NHS?
Weight loss typically begins after 2–4 weeks and continues gradually over months. Clinical trials showed sustained loss over 68–72 weeks. Combined with a reduced-calorie diet and increased activity, results are most significant. Track your progress using our free tool to monitor changes over time.
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.