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 and Elvanse — How They Compare for Weight Management
If you're considering Mounjaro or Elvanse for weight management in the UK, it's important to understand they work very differently. Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist, while Elvanse (lisdexamfetamine) is a stimulant medication primarily for ADHD. This guide explains how they work, their clinical uses, and why a GP or licensed prescriber must assess which, if any, is appropriate for your individual health. Use our free BMI calculator above to check where your weight sits on the NHS scale, then discuss your options with a healthcare professional.
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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 and Elvanse Work Differently
Mounjaro (tirzepatide) is a once-weekly injection licensed in the UK for weight management in eligible adults. It activates two natural hormone pathways — GIP and GLP-1 — which together may help reduce appetite, support feeling fuller after meals, and regulate how the body uses fat. In clinical trials (SURMOUNT-1), participants taking Mounjaro lost an average of 15–21% of their body weight over 72 weeks, alongside reduced-calorie diet and increased physical activity.
Elvanse (lisdexamfetamine) is a stimulant medication primarily licensed in the UK for ADHD in children and adults. It works by increasing dopamine and noradrenaline in the brain, improving focus and attention. Elvanse is not licensed for weight management and is not typically prescribed for weight loss. Some weight loss may occur as a side effect due to reduced appetite, but this is not its intended clinical purpose.
Key difference: Mounjaro is designed specifically for weight management via hormone activation. Elvanse is designed for ADHD symptom management via stimulant action. They are fundamentally different medication classes with different approved uses in the UK.
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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.
Eligibility and Prescribing in the UK
Mounjaro is available in the UK for adults with a BMI of 30 or above, or 27 or above with weight-related health conditions (type 2 diabetes, hypertension, or cardiovascular disease), following clinical assessment through NHS specialist services or private online prescribing with a licensed UK prescriber.
Elvanse is prescribed in the UK only for ADHD diagnosis following specialist psychiatric or developmental assessment. It is not indicated for weight loss. If you have been taking Elvanse for ADHD, weight changes are a side effect rather than the therapeutic intention.
If you're overweight or obese and interested in prescription weight management treatment, speak to your GP or a licensed prescriber about Mounjaro, Wegovy (semaglutide), or other options appropriate for your health profile. Try our free GLP-1 weight loss calculator to explore potential outcomes with different medications.
- 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 Elvanse used for weight loss in the UK?
No. Elvanse (lisdexamfetamine) is licensed only for ADHD treatment in the UK. It is not approved for weight management. Some people may experience weight loss as a side effect due to reduced appetite, but this is not its clinical purpose and Elvanse should not be prescribed specifically for weight loss.
Can I take Mounjaro and Elvanse together?
This is a question for your prescriber or GP. Both are potent medications with side effects that could interact. Any combination would require specialist assessment and close monitoring. Never combine medications without explicit medical guidance.
Which is more effective for weight loss — Mounjaro or Elvanse?
Mounjaro is specifically designed and clinically tested for weight management, with average weight loss of 15–21% in trials. Elvanse is not indicated for weight loss. If weight management is your goal, Mounjaro is the appropriate option — assessed through a licensed prescriber.
Can I get Mounjaro through the NHS in the UK?
Yes, through NHS specialist tier 3 weight management services following referral and assessment by your GP. Availability varies significantly by region and waiting times can be long. You can also access Mounjaro privately through online consultation with a licensed UK prescriber.
How do I know if Mounjaro is right for me?
A licensed prescriber or GP will assess your BMI, medical history, weight-related conditions, and current medications. Use our BMI calculator to check your baseline, then discuss eligibility with a healthcare professional who can provide personalised guidance.
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.