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
What Is Zepbound? Understanding Tirzepatide in the UK
Zepbound is the US brand name for tirzepatide, a prescription-only weight management injection now available in the UK under the brand name Mounjaro. This dual GIP and GLP-1 receptor agonist works by activating two natural hormone pathways to help regulate appetite and support weight loss alongside dietary changes and increased physical activity. If you're exploring weight management options in the UK, understanding how tirzepatide works and your eligibility is an important first step.
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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.
How Tirzepatide Works as a Weight Management Treatment
Tirzepatide is a dual GIP and GLP-1 receptor agonist — different from single GLP-1 medications like semaglutide (Wegovy). It activates two natural hormone pathways:
- GIP receptor activation: Helps regulate fat storage and metabolism
- GLP-1 receptor activation: Reduces appetite, supports feeling fuller after smaller meals, and slows how quickly food leaves your stomach
In clinical trials, tirzepatide helped participants lose an average of 15–21% of their body weight over 72 weeks — though individual results vary significantly. Weight loss is not assured and requires a reduced-calorie diet and increased physical activity alongside the medication. The GIP and GLP-1 receptor agonist combination is what distinguishes tirzepatide from other weekly weight loss injection options available in the UK.
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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.
UK Eligibility, Doses, and How to Access Tirzepatide
In the UK, tirzepatide (Mounjaro) may be prescribed for adults with a BMI of 30 kg/m² or above, or 27–29.9 kg/m² with weight-related health conditions such as type 2 diabetes, hypertension, or cardiovascular disease. Doses start at 2.5 mg weekly and increase gradually up to a maximum of 15 mg weekly. You can access tirzepatide through NHS specialist weight management services (following GP referral) or privately through a licensed UK prescriber following an online clinical assessment. Use our free BMI calculator to check whether you may meet initial eligibility criteria, and our GLP-1 weight loss calculator to explore potential outcomes at different doses.
- 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.
Is Zepbound the same as Mounjaro?
Yes. Zepbound is the US brand name for tirzepatide, while Mounjaro is the UK brand name for the same medication. In the UK, it's prescribed and referred to as Mounjaro. Both contain the same active ingredient and work identically.
How does tirzepatide differ from semaglutide (Wegovy)?
Tirzepatide is a dual GIP and GLP-1 receptor agonist, while semaglutide is a GLP-1 receptor agonist only. Clinical trials showed tirzepatide produced slightly higher average weight loss (15–21% vs approximately 15% for semaglutide), though individual results vary. Your prescriber will assess which is most appropriate for you.
What are the common side effects of tirzepatide?
Very common side effects include nausea, diarrhoea, vomiting, and constipation — usually most noticeable when starting or increasing doses. Most side effects reduce over time as your body adjusts. Always inform your prescriber of persistent or severe symptoms.
Can I get tirzepatide on the NHS in the UK?
Yes, tirzepatide (Mounjaro) is available through NHS specialist weight management services (tier 3). Access requires referral from your GP and assessment by a specialist service. Availability and waiting times vary significantly by region. Private access is also available through licensed UK prescribers.
How much weight can I expect to lose with tirzepatide?
Clinical trials showed average weight loss of 15–21% of body weight over 72 weeks at maximum doses, alongside a reduced-calorie diet and increased physical activity. Individual results vary considerably — some people lose more, some less. Weight loss is not assured, and your prescriber will discuss realistic expectations for your situation.
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.