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 Are Mounjaro Injections?
Mounjaro injections contain tirzepatide, a prescription-only weekly injection licensed in the UK for weight management in adults. Unlike single-mechanism medications, Mounjaro works as a dual GIP and GLP-1 receptor agonist—meaning it activates two natural hormone pathways to help regulate appetite and support feeling fuller after meals. Clinical trials showed participants lost an average of 15–21% of their body weight, though individual results vary significantly. You'll need a prescription and clinical assessment to access Mounjaro in the UK, either through NHS specialist weight management services or private prescribers.
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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's dual mechanism is what sets it apart from other weight loss injections like Wegovy (semaglutide), which work on the GLP-1 pathway alone. By targeting both GIP (glucose-dependent insulinotropic polypeptide) and GLP-1 receptors, Mounjaro may help reduce appetite more effectively for some people. The injection slows how quickly food leaves your stomach—though this effect typically lessens over time—and supports better fat utilisation.
You inject once weekly using a pre-filled KwikPen device into your stomach, thigh, or upper arm. Doses start at 2.5 mg and increase gradually every 4 weeks, up to a maximum of 15 mg weekly. Most people see noticeable appetite reduction within the first 2–4 weeks, but weight loss requires combined effort: Mounjaro works best alongside a reduced-calorie diet and increased physical activity. Results are not assured, and some people respond better than others.
- Injection site: stomach, thigh, or upper arm (rotate weekly)
- Frequency: once every 7 days
- Onset: appetite effects within 2–4 weeks; weight loss typically visible within 4–8 weeks
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.
Eligibility, Doses, and Side Effects in the UK
To access Mounjaro in the UK, you'll need a BMI of 30 kg/m² or above, or 27–29.9 kg/m² with a weight-related health condition such as type 2 diabetes, high blood pressure, abnormal cholesterol, sleep apnoea, or cardiovascular disease. Check your BMI using our free BMI calculator above. Adults of South Asian, Chinese, Black African, or Black Caribbean heritage may qualify at lower thresholds (BMI 27.5+)—this reflects higher health risks at lower weights in these groups.
Common side effects include nausea, diarrhoea, constipation, and stomach pain—usually mild and temporary as your body adjusts. Serious side effects are rare but include severe abdominal pain (possible pancreatitis), gallbladder problems, and serious allergic reactions. Nausea often decreases as your body adapts, typically within 2–4 weeks. Always inform your prescriber of all medications, as Mounjaro may affect oral contraceptive absorption.
- 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 Ozempic is approved for type 2 diabetes (up to 2 mg), while Wegovy is the licensed weight management version (up to 2.4 mg). Mounjaro contains tirzepatide, a different GLP-1 medicine—it's a dual GIP and GLP-1 receptor agonist, not semaglutide. Never use Ozempic for weight loss outside of medical supervision.
How much weight will I lose on Mounjaro?
Clinical trials showed average weight loss of 15–21% of body weight over 72 weeks at the highest dose. However, individual results vary significantly. Weight loss depends on your starting weight, diet, activity level, and how your body responds. Your prescriber can help estimate realistic outcomes based on your circumstances.
Can I get Mounjaro on the NHS?
Yes, NICE has approved Mounjaro for NHS use through specialist tier 3 weight management services. However, availability varies significantly by region, and waiting lists can be lengthy. Your GP can refer you to your local specialist service, though access is not assured everywhere in the UK.
What happens if I stop taking Mounjaro?
Weight regain is common after stopping, as appetite returns to baseline. Most people regain weight within months if they don't maintain diet and activity changes. Mounjaro is typically used long-term alongside lifestyle modifications, not as a short-term fix. Discuss stopping with your prescriber.
How do I store my Mounjaro pen?
Unopened pens must be stored in the fridge at 2–8°C and kept in their original carton. Once opened, pens can be stored at room temperature (below 30°C) for up to 30 days. Never freeze—if frozen, the pen cannot be used. Always check the expiry date before use.
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.