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 in the UK
Vyvanse (lisdexamfetamine) is a prescription stimulant medication primarily used to treat ADHD in the UK, not approved for weight management. While some people taking Vyvanse may experience weight loss as a side effect, it is not licensed or recommended by NHS for weight loss treatment. If you're interested in evidence-based weight management medication, UK-licensed options like Mounjaro and Wegovy are available for eligible adults. This guide explains the difference and what prescription weight loss support is actually available through the NHS.
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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.
UK-Licensed Weight Management Options
Unlike Vyvanse, the UK has three prescription medications specifically approved for weight management: Mounjaro (tirzepatide), Wegovy (semaglutide), and Saxenda (liraglutide). These are GLP-1 and GIP/GLP-1 receptor agonist medications with clinical evidence supporting their use for weight loss.
- Mounjaro: Dual GIP and GLP-1 agonist; average weight loss 15–21% body weight in clinical trials; once-weekly injection; doses 2.5–15 mg
- Wegovy: GLP-1 agonist only; average weight loss approximately 15% body weight; once-weekly injection; doses 0.25–2.4 mg
- Saxenda: GLP-1 agonist; average weight loss approximately 5–10% body weight; daily injection; doses 0.6–3 mg
All three require a clinical assessment to confirm eligibility. Adults with a BMI of 30 or above, or 27 or above with weight-related health conditions such as type 2 diabetes, high blood pressure, or cardiovascular disease, may qualify. Use our free BMI calculator to check whether you fall into an eligible weight range, and use our GLP-1 weight loss calculator to explore potential outcomes at different doses.
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.
How to Access Weight Loss Treatment in the UK
In the UK, weight management medication is accessed through two main routes. NHS access: referral from your GP to a tier 3 specialist weight management service; availability varies significantly by region and waiting lists can be lengthy. Private access: online consultation with a UK-licensed prescriber; no NHS referral needed; available within days; costs typically £129–£320 per month depending on dose and provider.
Start by speaking with your GP about whether prescription weight loss treatment might be appropriate for you. Your GP can assess your health, discuss your BMI and weight-related conditions, and advise whether NHS specialist services are available locally or whether private prescribing may be an option. Weight loss medication works best alongside a reduced-calorie diet and increased physical activity. Track your progress using our free progress tracker and weight converter to monitor results across different units.
- 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.
Why is Vyvanse not used for weight loss in the UK?
Vyvanse is a stimulant medication licensed in the UK specifically for ADHD, not for weight management. Although some people taking it may experience weight loss as a side effect, this is not its intended purpose and it is not recommended or approved for weight loss treatment. For evidence-based weight management, UK-licensed medications like Mounjaro and Wegovy are the appropriate options.
What's the difference between Vyvanse and weight loss injections like Wegovy?
Vyvanse is a stimulant that increases alertness and focus for ADHD; weight loss is an incidental side effect. Mounjaro and Wegovy are GLP-1 and GIP/GLP-1 agonists specifically designed to support weight management by reducing appetite and promoting fuller feeling. They have clinical trial evidence for weight loss and are licensed for this purpose in the UK.
Am I eligible for prescription weight loss medication on the NHS?
Adults with a BMI of 30 or above, or 27 or above with weight-related health conditions like type 2 diabetes or high blood pressure, may be eligible. NHS access is through specialist tier 3 weight management services—ask your GP for a referral. Eligibility varies by region and waiting lists can be long in many areas.
Can I get Mounjaro or Wegovy privately if I can't wait for NHS treatment?
Yes. Both medications are available through private online prescribing services after a clinical assessment with a UK-licensed prescriber. These are typically quicker than NHS specialist services but involve private costs ranging from approximately £129–£320 per month depending on the medication and dose.
How much weight loss should I expect from Mounjaro or Wegovy?
Clinical trials show average weight loss of approximately 15–21% body weight with Mounjaro and 15% with Wegovy. Results vary significantly between individuals and depend on adherence to medication, diet, and physical activity. Use our GLP-1 weight loss calculator to explore potential outcomes, but remember these are averages—your personal results may differ.
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.