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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Vyvanse and Weight Loss: What You Need to Know
Vyvanse (lisdexamfetamine) is a prescription stimulant medication primarily used to treat ADHD and binge eating disorder in the UK. While some people taking Vyvanse experience weight loss as a side effect, it is not licensed or recommended as a weight loss treatment. If you're looking to manage your weight, this guide explains how Vyvanse compares to licensed weight management options available in the UK, and what evidence-based approaches your GP can discuss with you.
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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 Vyvanse Affects Weight
Vyvanse is a stimulant medication that increases levels of noradrenaline and dopamine in the brain. This can suppress appetite as a side effect, which may lead to reduced food intake and weight loss in some people. However, weight changes vary considerably between individuals — some people maintain stable weight, whilst others may experience weight gain instead.
Vyvanse is not approved or marketed for weight management in the UK. Its primary indication is ADHD (attention deficit hyperactivity disorder) in adults and children, and binge eating disorder in adults. Using any medication for a purpose other than its licensed indication should only be done under close medical supervision and with explicit GP approval.
If weight loss occurs whilst taking Vyvanse for ADHD, this is an incidental effect, not the intended therapeutic outcome. Your GP will monitor your weight as part of routine ADHD care.
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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
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Vyvanse vs. Licensed Weight Loss Treatments in the UK
If you're seeking dedicated weight management treatment, the UK has prescription options specifically licensed and approved for weight loss. These include Wegovy (semaglutide), a once-weekly GLP-1 injection, and Mounjaro (tirzepatide), which combines GIP and GLP-1 mechanisms. Both require clinical assessment and are available through NHS specialist weight management services or private prescribing.
Unlike Vyvanse, these medications are designed to help regulate appetite and support weight loss alongside reduced-calorie diet and increased physical activity. Clinical trials have shown they can help participants lose 14–21% of body weight on average, though individual results vary. Try our free GLP-1 weight loss calculator to estimate potential outcomes with prescription weight loss medications, or use our BMI calculator to check whether you may be eligible for treatment.
Vyvanse carries different risks than weight loss medications — as a stimulant, it may increase heart rate and blood pressure, and has potential for dependence. Weight loss treatments like Wegovy and Mounjaro have their own side effect profiles, primarily gastrointestinal.
Always discuss any medication decision with your GP. If ADHD treatment is causing unintended weight changes that concern you, tell your prescriber — dose adjustments or alternative medications may be considered. For intentional weight management, your GP can refer you to NHS tier 3 specialist weight management services, where prescription weight loss treatments and tailored support are available. Weight loss is most effective when combining medication (if appropriate) with behaviour change, dietary support, and physical activity.
- 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.
Does Vyvanse cause weight loss?
Vyvanse may suppress appetite in some people, leading to weight loss as a side effect. However, weight changes vary — others may experience no change or weight gain. Vyvanse is not licensed for weight loss and should not be used for this purpose without GP approval.
Is Vyvanse a weight loss medication?
No. Vyvanse is licensed for ADHD and binge eating disorder, not weight management. If weight loss occurs, it's an incidental side effect, not the intended therapeutic effect. Licensed weight loss medications in the UK include Wegovy and Mounjaro.
Can I take Vyvanse to lose weight?
Using Vyvanse for weight loss is off-label use and should only be considered under explicit GP supervision, which is uncommon. Licensed, evidence-based weight loss treatments are safer and more appropriate options. Discuss weight management with your GP.
What are better alternatives to Vyvanse for weight loss?
Prescription options licensed for weight management in the UK include Wegovy (semaglutide) and Mounjaro (tirzepatide). Both are GLP-1 (or dual GIP/GLP-1) injections available through NHS specialist services or private prescribing. Check your BMI using our free BMI calculator to see if you may be eligible.
Should I mention weight changes if I'm taking Vyvanse?
Yes. Tell your GP or prescriber if Vyvanse is affecting your weight significantly — either loss or gain. They may adjust your dose, consider alternatives, or discuss whether intentional weight loss treatment is appropriate alongside ADHD management.
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.