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 Weight Loss Jabs — How They Work
Mounjaro weight loss jabs are a prescription-only injectable medicine used for weight management in UK adults. The active ingredient is tirzepatide, a dual GIP and GLP-1 receptor agonist that works differently from other weekly weight loss injections like Wegovy. Rather than a single mechanism, Mounjaro activates two natural hormone pathways to help reduce appetite, support feeling fuller after meals, and may assist with weight loss when combined with lifestyle changes. Access is through NHS specialist services or private prescribing following a clinical assessment. Results vary between individuals, and it's important to understand how this medication works before considering treatment.
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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 as a Weight Loss Jab
Mounjaro is a dual GIP and GLP-1 receptor agonist — meaning it activates two separate hormone pathways in your body. This dual action is what distinguishes it from single-mechanism injections. GIP (glucose-dependent insulinotropic polypeptide) and GLP-1 (glucagon-like peptide-1) are natural hormones your gut produces after eating.
When you use Mounjaro as a weekly weight loss injection, it:
- Reduces appetite and food cravings
- Helps you feel fuller after smaller portions
- Slows how quickly food leaves your stomach
- Supports better blood sugar regulation
In the SURMOUNT-1 clinical trial, participants taking Mounjaro 15 mg lost an average of approximately 20.9% of their body weight over 72 weeks — though results varied considerably between individuals. Weight loss occurred alongside a reduced-calorie diet and increased physical activity. Try our free GLP-1 weight loss calculator to see projected outcomes at different doses based on clinical trial data.
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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.
Mounjaro Eligibility and How to Access in the UK
To be eligible for Mounjaro in the UK, you typically need a BMI of 30 kg/m² or above, or a BMI of 27–29.9 with at least one weight-related health condition such as type 2 diabetes, high blood pressure, or cardiovascular disease. If you're of South Asian, Chinese, Black African, or Black Caribbean heritage, lower BMI thresholds may apply. Check your BMI instantly using our free BMI calculator above.
Mounjaro is available through two routes: NHS specialist weight management services (via GP referral to tier 3 services) and private prescribing (through registered online pharmacies following a clinical assessment). A prescriber will assess your individual health before issuing a prescription. The Mounjaro KwikPen device delivers a once-weekly injection, with doses ranging from 2.5 mg to 15 mg, typically titrated over 20 weeks. Track your progress using our free progress tracker as you adjust 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.
What's the difference between Mounjaro and Wegovy weight loss jabs?
Both are prescription weight loss injections, but Mounjaro (tirzepatide) uses a dual GIP + GLP-1 mechanism, while Wegovy (semaglutide) is a single GLP-1 agonist. Mounjaro has a higher maximum dose (15 mg vs 2.4 mg) and clinical trials showed slightly higher average weight loss. Both require a prescription and clinical assessment. Individual results vary, and either may be appropriate depending on your health profile.
Can I get Mounjaro weight loss jabs on the NHS in the UK?
Yes, Mounjaro is available through NHS specialist tier 3 weight management services. Access requires a GP referral and assessment by a specialist team. However, NHS availability varies significantly by region, and waiting times can be lengthy in many areas. Private prescribing via registered online pharmacies offers faster access but involves private costs ranging from approximately £150–£300 per month depending on dose.
How much weight will I lose with Mounjaro jabs?
Clinical trials showed average weight loss of approximately 15–21% of body weight, but individual results vary significantly. Some people lose more, others less. Weight loss depends on your starting weight, how well you tolerate the dose, your adherence to a reduced-calorie diet, and physical activity levels. Your GP or prescriber can discuss realistic expectations based on your personal circumstances.
What are the main side effects of Mounjaro weight loss jabs?
Very common side effects include nausea, diarrhoea, vomiting, and stomach pain — usually mild and temporary as your body adjusts. Less common side effects include fatigue, dizziness, and injection site reactions. Serious side effects are rare but can include severe stomach pain (possible pancreatitis) or gallbladder problems. Always report persistent symptoms to your prescriber.
Is Mounjaro the same as the injection used for type 2 diabetes?
Mounjaro (tirzepatide) is approved specifically for weight management in the UK. It's different from Ozempic, which contains semaglutide and is approved for type 2 diabetes. Don't confuse weight loss injections with diabetes medications — they work differently and have different dosing schedules. Always use the medication prescribed for your specific condition.
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.