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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Mounjaro Advice: Everything UK Adults Need to Know
If you're considering Mounjaro (tirzepatide) for weight management, you'll want clear, practical advice on how it works, who can access it, and what to expect. Mounjaro is a prescription-only once-weekly injection licensed in the UK for adults with a BMI of 30 or above, or 27 or above with weight-related health conditions. This guide provides evidence-based information to help you understand whether Mounjaro might be right for you and how to access it through NHS or private routes.
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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.
How Mounjaro Works and What to Expect
Mounjaro (tirzepatide) works differently to other weight loss injections because it's a dual GIP and GLP-1 receptor agonist. This means it activates two natural hormone pathways in your body — GIP (glucose-dependent insulinotropic polypeptide) and GLP-1 (glucagon-like peptide-1) — rather than just one like Wegovy (semaglutide). This dual action may help reduce appetite, decrease food cravings, and help you feel fuller after smaller meals. Mounjaro also slows how quickly food leaves your stomach, though this effect typically reduces over time.
In the SURMOUNT-1 clinical trial, participants taking the highest dose (15 mg) lost an average of approximately 20.9% of their body weight over 72 weeks, alongside a reduced-calorie diet and increased physical activity. However, individual results vary significantly — some people lose more, some less. Weight loss is not assured, and the medication works best when combined with lifestyle changes, not instead of them.
You can use our GLP-1 weight loss calculator to estimate potential weight loss at different Mounjaro doses based on your starting weight.
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.
UK Eligibility, Doses, and Access Routes
In the UK, you may be eligible for Mounjaro if you have a BMI of 30 or above, or 27 or above with weight-related conditions like type 2 diabetes, high blood pressure, or sleep apnoea. Adults of South Asian, Chinese, Black African, or Black Caribbean heritage may qualify at lower BMI thresholds (27.5 or above) because these groups face higher health risks at lower weights. Mounjaro doses start at 2.5 mg and escalate every 4 weeks to a maximum of 15 mg once weekly.
NHS access: Through tier 3 specialist weight management services — waiting times vary by region. Private access: Through GPhC-registered online pharmacies with clinical assessment (typically £129–£320/month depending on dose). Your prescriber will assess whether tirzepatide is suitable for your individual health before 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.
Is Mounjaro the same as Ozempic?
No. Both contain semaglutide, but Mounjaro is Novo Nordisk's brand name for semaglutide, while Ozempic is approved for type 2 diabetes only (doses up to 2 mg). Mounjaro is the licensed brand for weight management. Tirzepatide (Mounjaro's active ingredient) is different — it's a dual GIP+GLP-1 agonist, not a GLP-1 agonist alone.
What are the most common Mounjaro side effects in the UK?
Very common side effects include nausea, diarrhoea, vomiting, and constipation. Most people experience stomach discomfort, especially when starting or increasing the dose. These typically improve over time. Less commonly, people report fatigue, dizziness, headache, or hair loss. Serious side effects like severe stomach pain (possible pancreatitis) require immediate medical attention.
How much weight will I lose on Mounjaro?
Clinical trials showed an average of 15–clinically studied weight loss depending on dose, alongside diet and exercise. However, individual results vary significantly. Some people lose more, some less. Weight loss depends on your starting weight, genetics, adherence, diet, and activity level. Your prescriber can discuss realistic expectations for your situation.
Can I get Mounjaro through the NHS in the UK?
Yes, Mounjaro is available through NHS tier 3 specialist weight management services. You need a GP referral and assessment by a specialist service. Availability varies significantly by region (ICB) and waiting lists can be months to years in some areas. Private prescription is available faster through regulated online pharmacies.
What's the difference between Mounjaro and Wegovy?
Mounjaro (tirzepatide) is a dual GIP+GLP-1 agonist; Wegovy (semaglutide) is GLP-1 only. Mounjaro starts at 2.5 mg and goes to 15 mg; Wegovy starts at 0.25 mg and goes to 2.4 mg. SURMOUNT trials showed Mounjaro at 15 mg achieved ~clinically studied weight loss vs STEP trials showing Wegovy ~clinically studied weight loss. Both require prescription and clinical assessment.
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.