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 The Mounjaro Injection?
Mounjaro is a prescription-only weekly weight loss injection licensed in the UK for adults with obesity or overweight with health conditions. It contains tirzepatide, a dual GIP and GLP-1 receptor agonist that works by regulating appetite and helping you feel fuller after smaller meals. Unlike some other weight management approaches, Mounjaro requires a clinical assessment before prescription and works best alongside a reduced-calorie diet and increased physical activity. Understanding what it is, how it works, and your access options is the first step to deciding if this treatment might be right for you.
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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 Mounjaro Works & What to Expect
Mounjaro works by activating two natural hormone pathways — GIP (glucose-dependent insulinotropic polypeptide) and GLP-1 (glucagon-like peptide-1) — which regulate appetite and blood sugar. This dual mechanism is what differentiates it from other weight loss injections like Wegovy, which activate GLP-1 alone. The medication slows gastric emptying, meaning food stays in your stomach longer, helping you feel satisfied with smaller portions. You inject it once weekly using a pre-filled KwikPen device into your stomach, thigh, or upper arm. Treatment involves gradual dose escalation starting at 2.5 mg, increasing every 4 weeks up to a maximum of 15 mg. In clinical trials, participants lost an average of 15–21% of their body weight — though individual results vary significantly. Common side effects include nausea, diarrhoea, and constipation, particularly during dose increases. Most people adjust within a few weeks as the body adapts to the medication.
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.
Accessing Mounjaro in the UK — Cost & Routes
In the UK, you can access Mounjaro through two main routes. The NHS route involves referral to a specialist tier 3 or tier 4 weight management service, but availability varies significantly by region and waiting lists can be lengthy. NICE has approved Mounjaro for specialist NHS use, but access depends on your local Integrated Care Board (ICB). The private route is available through GPhC-registered online pharmacies following an online clinical assessment with a UK-licensed prescriber. Private costs typically range from £129–£320 per month depending on your dose, with no NHS referral required. Regardless of route, a prescriber will assess whether Mounjaro is suitable based on your BMI, health conditions, and current medications. You can use our free BMI calculator to check your starting point before seeking an assessment.
- 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.
How much does Mounjaro cost on the NHS?
Mounjaro is available through NHS specialist weight management services for eligible patients, but there is no direct patient cost. However, NHS access is limited and varies by region — many areas have significant waiting lists. Private prescription costs typically range from £129–£320 per month depending on your dose.
What's the difference between Mounjaro and Wegovy?
Both are once-weekly weight loss injections licensed in the UK. Mounjaro (tirzepatide) activates dual GIP and GLP-1 pathways and may deliver slightly higher average weight loss (15–21% vs ~15% for Wegovy). Wegovy (semaglutide) activates GLP-1 alone. Both require clinical assessment and are prescription-only. Choice depends on individual suitability and prescriber recommendation.
How do I get a Mounjaro prescription privately in the UK?
Register with an online GPhC-registered pharmacy offering Mounjaro consultations. Complete an online medical questionnaire and consultation with a UK-licensed prescriber. If approved, you'll receive a prescription and the medication is dispensed by the pharmacy. The entire process typically takes 24–48 hours. Always ensure the provider is registered with the General Pharmaceutical Council.
What eligibility criteria apply for Mounjaro in the UK?
You must be 18 or over with a BMI of 30 kg/m² or above, or BMI 27–29.9 with at least one weight-related health condition (type 2 diabetes, prediabetes, high blood pressure, high cholesterol, sleep apnoea, or heart disease history). South Asian, Chinese, Black African, and Black Caribbean adults may have slightly lower BMI thresholds. Your GP or prescriber can assess your individual eligibility.
How long does it take to see weight loss results on Mounjaro?
Most people notice appetite changes within days to weeks, but significant weight loss typically develops gradually over months. Clinical trial results showed meaningful weight loss by 12 weeks, with continued loss over a full year. Weight loss depends on dose, adherence, diet, and physical activity — individual results vary considerably. Track your progress using our free progress tracker alongside treatment.
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.