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
Free tracker included with every download this week
Eating Weight Loss Plan With UK Prescription Medication
An eating weight loss plan works best when combined with proven medical support if you're eligible. In the UK, prescription weight loss medications like Mounjaro and Wegovy are now available through NHS specialist services and private prescribing for adults meeting specific health criteria. This guide explains how UK-licensed medications fit into a comprehensive weight management strategy, eligibility thresholds, and how to explore your options with your GP. We'll also show you how to calculate your starting point using your current BMI and weight.
10,000+ calculations today · NHS-aligned thresholds · 100% free
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 Prescription Weight Loss Options
Three prescription weight loss medications are licensed in the UK for 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 sleep apnoea. Mounjaro (tirzepatide) is a once-weekly dual GIP and GLP-1 receptor agonist injection. In clinical trials, participants on the maximum 15mg dose lost an average of approximately 21% of their body weight over 72 weeks, alongside a reduced-calorie diet and increased physical activity. Wegovy (semaglutide) is a once-weekly GLP-1 injection that helped participants lose around 15% of their body weight on average in clinical trials. Saxenda (liraglutide) is a daily GLP-1 injection option. All three are prescription-only medicines requiring a clinical assessment before being prescribed. Our free GLP-1 weight loss calculator can help you understand potential outcomes at different dose levels, though individual results vary significantly.
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 and Getting Started
In the UK, you can access prescription weight loss medication through two routes. The NHS route involves requesting a referral from your GP to a specialist tier 3 weight management service, though availability varies by region and waiting times can be lengthy. The private route uses online consultations with UK-licensed prescribers followed by dispensing through registered pharmacies. Before starting any medication, your weight management plan should include dietary changes, increased physical activity, and behavioural support. Use our free BMI calculator to understand your current health category, and our weight converter to track progress in your preferred units. Your GP can discuss whether prescription support is appropriate for your individual circumstances alongside lifestyle changes.
- 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 BMI do I need to be eligible for prescription weight loss medication in the UK?
Adults with a BMI of 30 or above are generally eligible. If your BMI is 27–29.9 and you have weight-related health conditions (type 2 diabetes, high blood pressure, sleep apnoea, or cardiovascular disease), you may also qualify. For adults of South Asian, Chinese, Black African, or Black Caribbean heritage, lower BMI thresholds may apply due to higher health risks at lower weights.
How much weight can I expect to lose with Mounjaro or Wegovy?
Clinical trial averages show Mounjaro users lose around 15–21% of body weight, and Wegovy users lose around 14–15%, over 68–72 weeks. However, individual results vary significantly based on dose, adherence, diet, and physical activity. These medications work best alongside a reduced-calorie eating weight loss plan, not as a replacement for lifestyle changes.
Can I get prescription weight loss medication through the NHS?
Yes, through specialist tier 3 weight management services. You'll need a GP referral. Availability and waiting times vary significantly by region. Some areas have shorter waits than others. Private online prescribing offers faster access if you meet eligibility criteria and prefer this route.
What's the difference between Mounjaro and Wegovy?
Mounjaro is a dual GIP and GLP-1 agonist (maximum 15mg weekly), while Wegovy is a GLP-1 agonist only (maximum 2.4mg weekly). Mounjaro clinical trials showed slightly higher average weight loss, but both are effective. Choice depends on individual suitability, assessed by your prescriber following a clinical consultation.
Do I still need to diet if I take a weight loss injection?
Yes. Prescription weight loss medications are most effective alongside a reduced-calorie eating weight loss plan and regular physical activity. Medications support appetite control and satiety, but they work best as part of a comprehensive approach. Your weight management plan should include all three elements: medication, diet, and exercise.
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.