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 Injections with Tirzepatide — NHS & UK Information
Tirzepatide, marketed as Mounjaro, is a prescription-only weight loss injection available in the UK through both NHS specialist services and private prescribing. This once-weekly GLP-1 receptor agonist and GIP receptor agonist may help support weight management alongside lifestyle changes. Understanding NHS eligibility criteria, how tirzepatide works, and the difference between NHS and private access routes can help you decide if this treatment is 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.
NHS Eligibility & Tier 3 Weight Management Services
In the UK, tirzepatide (Mounjaro) is prescribed through NICE-approved specialist tier 3 weight management services, typically accessed via referral from your GP. Eligibility criteria include: BMI of 30 kg/m² or above, or BMI of 27–29.9 with weight-related health conditions such as type 2 diabetes, high blood pressure, or sleep apnoea. For adults of South Asian, Chinese, Black African, or Black Caribbean heritage, lower BMI thresholds apply (from 27.5 kg/m²).
Access varies significantly by region and waiting lists can be lengthy in many areas. Your GP will assess your eligibility and make a referral to your local specialist service if appropriate. Use our free BMI calculator to check where your current weight falls on the NHS BMI scale, and our GLP-1 weight loss calculator to explore potential outcomes with tirzepatide at different doses.
Clinical trials showed that tirzepatide helped participants lose an average of 15–21% of their body weight—though individual results vary considerably and depend on dose, diet, and physical activity.
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.
Private Access vs NHS: Key Differences for Tirzepatide
NHS route: Free through specialist tier 3 services following GP referral; significant regional variation in availability; potential waiting lists of months or longer. Private route: Online consultation with a UK-licensed prescriber; prescription issued if clinically appropriate; dispensed by GPhC-registered pharmacies; available without NHS referral; costs typically range from £129–£320 per month depending on dose.
Both routes require a clinical assessment confirming you meet eligibility criteria. Neither route offers tirzepatide without a valid prescription from a UK-licensed healthcare professional. If you're considering private access, ensure the provider is regulated by the General Pharmaceutical Council (GPhC). Track your progress with our free progress tracker whether you access tirzepatide through NHS or private prescribing.
- 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 exactly is tirzepatide and how does it work?
Tirzepatide is a dual GIP and GLP-1 receptor agonist—it activates two natural hormone pathways that regulate appetite, food cravings, and how quickly food leaves your stomach. This dual mechanism may be more effective than single GLP-1 agonists. It is not insulin and does not work the same way as diabetes medications, though it can help with blood sugar control as a side benefit.
Can I get tirzepatide (Mounjaro) on the NHS in the UK?
Yes, tirzepatide is NICE-approved and available through NHS specialist tier 3 weight management services. You must be referred by your GP and meet eligibility criteria (BMI ≥30, or BMI 27–29.9 with weight-related conditions). Availability and waiting times vary significantly by region. Your GP can advise on local access.
What weight loss can I realistically expect with tirzepatide?
Clinical trials showed average weight loss of 15–21% of body weight over 72 weeks—but individual results vary significantly. Some people lose more, some less. Results depend on dose, adherence, diet, physical activity, and individual metabolism. Your prescriber will discuss realistic expectations based on your circumstances.
How much does tirzepatide cost privately in the UK?
Private tirzepatide (Mounjaro) typically costs £129–£320 per month depending on dose, with higher doses (10–15 mg) costing more than lower doses (2.5–5 mg). Prices vary between GPhC-registered providers. The NHS route is free but requires GP referral and tier 3 service access.
What are the main side effects of tirzepatide (Mounjaro)?
Very common side effects include nausea, diarrhoea, vomiting, constipation, and stomach pain—these usually decrease over time. Common side effects include indigestion, fatigue, dizziness, and injection site reactions. Serious side effects are rare but include severe stomach pain (possible pancreatitis) and gallbladder problems. Always report concerning 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.