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 — UK Safety Information
If you're taking Elvanse (lisdexamfetamine) for ADHD and considering Mounjaro (tirzepatide) for weight management, it's important to understand how these medications interact. Both are prescription-only medicines in the UK, and using them together requires careful medical assessment. This guide explains what you need to know about combining these medications, based on UK prescribing guidance and clinical evidence. Always consult your GP or healthcare professional before starting any new medication, especially if you're already taking another prescription drug.
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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 Together
Mounjaro is a dual GIP and GLP-1 receptor agonist that works on appetite and blood sugar regulation in the gut and brain. Elvanse (lisdexamfetamine) is a stimulant medication that works on dopamine and noradrenaline in the central nervous system for ADHD management. These medications work through completely different pathways, which is why they are not contraindicated together.
However, combining them requires careful monitoring because:
- Stimulant medications like Elvanse can increase heart rate and blood pressure
- Mounjaro may cause nausea and gastric effects that could interact with Elvanse's appetite suppression
- Both medications may independently cause dizziness or fatigue, which could compound if combined
- There is limited clinical trial data on using these two medications together specifically
Your GP or prescriber needs to assess your individual health profile, blood pressure, heart rate, and medical history before confirming it's safe to use both medications at the same time.
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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.
NHS Guidance and What Your GP Needs to Know
The UK Medicines and Healthcare products Regulatory Agency (MHRA) does not list any absolute contraindication between Mounjaro (tirzepatide) and Elvanse (lisdexamfetamine). However, both are prescription-only medicines requiring specialist oversight. Your GP or NHS weight management specialist needs to know your complete medication history, including Elvanse dosing, before prescribing Mounjaro.
If you're accessing Mounjaro through an NHS tier 3 weight management service, inform your specialist immediately that you take Elvanse. If using a private prescriber online, you must disclose all current medications during your clinical assessment. Never start or stop either medication without professional guidance. Your heart rate, blood pressure, and appetite levels should be monitored regularly when using both medications together, particularly during the initial Mounjaro dose titration phase.
- 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.
Can I take Mounjaro if I'm on Elvanse for ADHD?
Potentially yes, but only with explicit approval from your GP or prescriber. These medications work through different mechanisms, so there's no absolute contraindication. However, your healthcare professional must assess your individual cardiovascular health, current Elvanse dose, and overall medical history before confirming it's safe. Never assume it's okay — always disclose Elvanse use during any Mounjaro clinical assessment.
Will Mounjaro reduce the effectiveness of Elvanse?
Mounjaro may slow gastric emptying (stomach function), which could theoretically affect how quickly Elvanse is absorbed. However, there's no clinical evidence that Mounjaro reduces Elvanse efficacy. If you notice changes in ADHD symptom control after starting Mounjaro, report this to your GP immediately. Dose adjustments to either medication may be needed.
What side effects might I experience combining Mounjaro and Elvanse?
Mounjaro commonly causes nausea, diarrhoea, and appetite loss. Elvanse commonly causes appetite suppression and increased heart rate. Together, these could amplify appetite suppression or nausea. You may also experience increased dizziness or fatigue. Close monitoring by your GP during the first 4–8 weeks is essential to check whether side effects are tolerable.
Do I need to adjust my Elvanse dose when starting Mounjaro?
Not necessarily, but your prescriber may recommend monitoring. Mounjaro's effects on appetite and nausea could make your current Elvanse dose feel different. Some people find they tolerate their usual dose well; others may need adjustments. Your GP or ADHD specialist should review your Elvanse dosing after you've been on Mounjaro for 2–4 weeks.
Should I use the BMI calculator or weight loss calculator if I'm on both medications?
Yes. Our free BMI calculator and GLP-1 weight loss calculator are tools to track your health metrics and estimate potential weight loss progression. However, because you're on Elvanse, your actual weight loss may differ from standard projections due to the appetite-suppressing effects of the stimulant. Use the tools for baseline tracking, but discuss realistic expectations with your prescriber given your ADHD medication.
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.