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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Vitality Weight Loss — UK Prescription Medication Options
Vitality weight loss through prescription medication is now available to eligible UK adults. If you're looking for evidence-based weight management support beyond diet and exercise alone, several prescription options exist through both NHS and private routes. This guide covers UK-licensed medications, eligibility criteria, and how to find out if you qualify for prescription weight loss treatment.
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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 Loss Medications
Three prescription-only medications are currently licensed in the UK for weight management in adults:
- Mounjaro (tirzepatide) — A dual GIP and GLP-1 receptor agonist, injected once weekly. In clinical trials, participants lost an average of 15–21% of their body weight over 72 weeks when used alongside diet and exercise changes.
- Wegovy (semaglutide) — A GLP-1 receptor agonist, injected once weekly. Clinical trial data showed average weight loss of around 15% of body weight at the maximum dose.
- Saxenda (liraglutide) — A daily GLP-1 injection (three times larger needle frequency than the weekly options). Average weight loss ranges from 5–10% of body weight.
All three are prescription-only and require a clinical assessment before being prescribed. Results vary significantly between individuals — these figures represent trial averages, not assured outcomes. Each medication works by regulating appetite hormones and helping you feel fuller for longer alongside a reduced-calorie diet and increased physical activity.
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.
NHS vs Private Access Routes
NHS access is through specialist tier 3 weight management services — not standard GP prescription. You'll typically need a GP referral and may face significant waiting lists depending on your local integrated care board. NHS availability varies substantially across regions.
Private access is available through GPhC-registered online prescribing services following an online clinical assessment with a UK-licensed prescriber. This route doesn't require an NHS referral and has no waiting list. To explore which option suits you, start by discussing weight management with your GP — they can assess eligibility and explain local NHS provision. You can also independently seek a private clinical assessment online. Our GLP-1 weight loss calculator can help you understand potential outcomes at different doses if you progress to prescription treatment.
Eligibility for prescription weight loss treatment generally requires a BMI of 30 kg/m² or above, or BMI of 27–29.9 with weight-related health conditions such as type 2 diabetes, high blood pressure, or sleep apnoea. If you're of South Asian, Chinese, Black African, or Black Caribbean heritage, lower BMI thresholds may apply. Check your personal BMI using our free BMI calculator above — this gives you a clear starting point for your GP conversation. A prescriber will assess whether medication is appropriate based on your individual health profile, not BMI alone.
- 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.
What's the difference between Mounjaro and Wegovy for weight loss?
Both are once-weekly injections, but Mounjaro uses a dual mechanism (GIP and GLP-1 agonist) whilst Wegovy uses GLP-1 alone. Clinical trials suggest Mounjaro may achieve slightly higher average weight loss (15–21% vs 15%), but individual results vary. Your prescriber will recommend the most suitable option based on your health profile.
Can I access prescription weight loss medication through my NHS GP?
Prescription weight loss medications are typically available through NHS specialist tier 3 weight management services, not standard GP prescription. You'll need a GP referral and assessment. Access varies by region — ask your GP about local provision and waiting times. Private online prescribing is an alternative route without waiting lists.
How quickly will I lose weight on Mounjaro or Wegovy?
NHS recommends losing 0.5–1 kg per week for sustainable results. Clinical trial participants on Mounjaro or Wegovy typically saw meaningful weight loss within 8–12 weeks, but individual timelines vary greatly. Results depend on your starting weight, dose, diet, and activity levels. A prescriber can give personalised projections.
What happens if I stop taking a weight loss injection?
Weight loss effects gradually reverse — most people regain weight within weeks to months of stopping. These medications are designed for long-term use alongside sustained lifestyle changes. Discuss duration and goals with your prescriber to plan sustainable management.
Are there side effects with prescription weight loss injections?
Common side effects include nausea, diarrhoea, constipation, and stomach pain — usually mild and temporary. Serious side effects are rare but can include pancreatitis symptoms or severe allergic reactions. Your prescriber will discuss all risks and monitor you throughout treatment.
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.