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
Should I Go On Mounjaro? What You Need to Know
Whether Mounjaro is right for you depends on your BMI, health conditions, and personal circumstances. This dual GIP and GLP-1 receptor agonist injection may help with weight management if you meet NHS eligibility criteria, but it's not suitable for everyone. This guide explains how to decide whether to pursue Mounjaro treatment with your GP or a licensed prescriber.
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.
Who Is Eligible For Mounjaro in the UK?
Mounjaro (tirzepatide) is a prescription-only injection licensed for weight management in UK adults who meet specific criteria. You may be eligible if you have a BMI of 30 kg/m² or above, or a BMI of 27–29.9 kg/m² alongside at least one weight-related health condition such as type 2 diabetes, prediabetes, high blood pressure, or cardiovascular disease.
If you're of South Asian, Chinese, Black African, or Black Caribbean heritage, lower BMI thresholds may apply — your prescriber can assess this. Mounjaro cannot be prescribed if you're under 18, pregnant, breastfeeding, or have a history of severe medullary thyroid cancer or multiple endocrine neoplasia type 2.
Use our free BMI calculator above to check where your BMI falls, and our GLP-1 weight loss calculator to estimate potential outcomes at different doses.
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.
How Does Mounjaro Work and What Results Can You Expect?
Mounjaro works as a dual GIP and GLP-1 receptor agonist — activating two natural hormone pathways that regulate appetite and blood sugar. This dual mechanism may help reduce food cravings, support feeling fuller after meals, and slow gastric emptying. In the SURMOUNT-1 clinical trial, participants lost an average of 15–21% of their body weight over 72 weeks, though individual results vary significantly.
Weight loss is not assured and depends on adherence, diet, exercise, and individual metabolism. Results typically take 4–8 weeks to become noticeable. Mounjaro is injected once weekly using a Mounjaro KwikPen, with doses escalated gradually from 2.5 mg up to a maximum of 15 mg.
- 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 are the main side effects of Mounjaro?
Very common side effects include nausea, diarrhoea, vomiting, and constipation — usually mild and short-lived. Less common effects include fatigue, dizziness, injection site reactions, and hair loss. Serious side effects are rare but include severe stomach pain (possible pancreatitis) and severe allergic reactions. Your prescriber will discuss risks before starting.
Can I get Mounjaro on the NHS in the UK?
Mounjaro is available through NHS specialist tier 3 weight management services, but access varies by region and waiting lists can be very long. You'll typically need a GP referral. Alternatively, it's available privately through UK-licensed online prescribers following a clinical assessment and prescription from a GPhC-registered pharmacy.
How does Mounjaro compare to Wegovy?
Mounjaro (tirzepatide) is a dual GIP+GLP-1 agonist, while Wegovy (semaglutide) is a GLP-1-only agonist. Mounjaro achieved slightly higher average weight loss (15–21%) compared to Wegovy (approximately 15%) in clinical trials. Both are once-weekly injections, but Mounjaro doses are different and escalate more gradually. Results vary between individuals.
Will I need to stay on Mounjaro forever?
Mounjaro is typically used for ongoing weight management rather than short-term treatment. If you stop taking it, appetite-regulating effects diminish over time and weight may return. Your prescriber will discuss long-term use and whether this medication suits your goals. Combining Mounjaro with sustainable lifestyle changes is essential.
How do I start Mounjaro in the UK?
Contact your GP about referral to a specialist weight management service (NHS route), or book a consultation with a UK-licensed online prescriber (private route). You'll have a clinical assessment to check eligibility, discuss health conditions and medications, and confirm it's appropriate for you. A prescription is then issued by a registered 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.