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 Mounjaro Weight Loss Jab?
Mounjaro is a prescription-only weekly weight loss injection licensed in the UK for adults with obesity or overweight with related health conditions. It contains tirzepatide, which works as a dual GIP and GLP-1 receptor agonist — activating two natural hormone pathways to help regulate appetite and support feeling fuller after meals. Unlike some weight loss injections, Mounjaro's dual mechanism may offer greater appetite suppression. You'll need a clinical assessment from a licensed prescriber before starting treatment, and results vary significantly between individuals.
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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 and Expected Results
Mounjaro works by mimicking two natural hormones: GIP (glucose-dependent insulinotropic polypeptide) and GLP-1 (glucagon-like peptide-1). Together, these help signal to your brain that you're full, reduce cravings, and slow how quickly food leaves your stomach. This dual action differentiates it from single-mechanism GLP-1 injections like Wegovy.
In the SURMOUNT clinical trial, participants using Mounjaro at the maximum 15mg dose lost an average of 20.9% of their body weight over 72 weeks — though individual results vary. Lower doses (5mg and 10mg) showed average losses of approximately 15% and 19.5% respectively. These results were achieved alongside a reduced-calorie diet and increased physical activity, not through the injection alone.
You can estimate your potential weight loss using our free GLP-1 weight loss calculator, which projects outcomes at different dose levels.
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 How to Access
In the UK, you may be eligible for Mounjaro if you have a BMI of 30 or above, or BMI of 27–29.9 with weight-related conditions such as type 2 diabetes, high blood pressure, or heart disease. For South Asian, Black African, or Black Caribbean adults, lower BMI thresholds apply (27.5+).
Mounjaro comes as a pre-filled KwikPen and is injected once weekly, starting at 2.5mg and increasing gradually to a maximum of 15mg over several months. Each pen contains four weeks of doses. Access is through NHS specialist weight management services (tier 3) with potentially long waiting lists, or privately via online prescribing following a clinical assessment. Your GP can advise you on NHS access in your area.
- 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 or Wegovy?
No. Mounjaro (tirzepatide) is a dual GIP and GLP-1 injection. Ozempic contains semaglutide and is approved for diabetes, not weight loss. Wegovy is also semaglutide but at a weight management dose — it's a single GLP-1 mechanism. Mounjaro's dual action may offer different appetite suppression compared to Wegovy, though individual responses vary.
What are the main side effects of Mounjaro?
Very common side effects include nausea, diarrhoea, vomiting, and constipation — usually mild and temporary. Indigestion, injection site reactions, and fatigue are also common. Serious side effects are rare but include severe stomach pain (possible pancreatitis) and gallbladder problems. Always report severe symptoms to your GP or prescriber immediately.
How do I inject Mounjaro?
Mounjaro is a pre-filled KwikPen. You inject once weekly into your stomach, upper thigh, or upper arm (arm requires assistance). Rotate injection sites each week. Unopened pens store in the fridge at 2–8°C. After first use, you can keep the pen at room temperature below 30°C for up to 30 days.
Can I get Mounjaro on the NHS in the UK?
NHS access is through specialist tier 3 weight management services, not standard GP prescription. You'll need a referral from your GP. Availability and waiting times vary significantly by region (ICB). Many areas have long waiting lists. Private prescribing via online consultation is faster but costs approximately £129–£320 monthly depending on dose.
Will I need to use MyWeightCheck's BMI calculator to check eligibility?
Our free BMI calculator helps you understand your starting point and track changes, but it's not a clinical assessment. Your GP or prescriber will formally assess your BMI, health conditions, and suitability during your consultation. Use the calculator to understand your current BMI range — it's a useful baseline for your discussion.
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.