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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Weight Loss Trials in the UK: Prescription Medication Options
Weight loss trials in the UK have led to several prescription medications now available for eligible adults. If you're considering weight management medication, understanding what's available, how it works, and whether you qualify is essential. The UK's prescription weight loss options include medications that have undergone rigorous clinical trials and are now licensed for use. Your GP can help assess whether you're eligible and which option might suit your situation. Start by checking your BMI using our free BMI calculator to understand your starting point.
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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.
UK-Licensed Weight Loss Medications Approved for Weight Management
Three main prescription weight loss medications are currently licensed in the UK for adults meeting eligibility criteria:
- Mounjaro (tirzepatide) — a dual GIP and GLP-1 receptor agonist injection given once weekly. Clinical trials showed participants lost an average of 15–21% of their body weight over 72 weeks alongside diet and exercise.
- Wegovy (semaglutide) — a GLP-1 receptor agonist injection given once weekly. The STEP clinical trials demonstrated average weight loss of approximately 15% of body weight, with some participants achieving higher results.
- Saxenda (liraglutide) — a GLP-1 receptor agonist given by daily injection. Clinical evidence supports weight loss of around 5–10% of body weight for most users.
All three are prescription-only medicines requiring a clinical assessment before use. Individual results vary significantly based on adherence, diet, and physical activity levels.
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 Eligibility Criteria
Eligibility for prescription weight loss medication in the UK includes:
- BMI of 30 kg/m² or above, or BMI 27–29.9 with a weight-related health condition (type 2 diabetes, high blood pressure, sleep apnoea, cardiovascular disease)
- Lower thresholds apply for adults of South Asian, Chinese, Black African, or Black Caribbean heritage (BMI 27.5+)
- Adults aged 18 and over who are not pregnant or breastfeeding
NHS access: Through specialist tier 3 weight management services (waiting lists vary by region). Private access: Through GPhC-registered online prescribers following a clinical assessment. Both routes require a prescription from a licensed UK prescriber. Use our GLP-1 weight loss calculator to explore potential outcomes at different doses.
- 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?
Mounjaro (tirzepatide) is a dual GIP and GLP-1 agonist with average weight loss of 15–21%, while Wegovy (semaglutide) is a GLP-1-only agonist with average weight loss around 15%. Both are once-weekly injections. Mounjaro's dual mechanism may offer slightly greater average results, though individual responses vary. Your prescriber will advise which is suitable for you.
Can I get weight loss medication on the NHS?
Yes, if you meet eligibility criteria and are referred to an NHS specialist weight management service (tier 3). Availability and waiting times vary by region. Your GP can discuss referral options. Private prescription is available without NHS referral through approved online prescribers, though this involves a cost.
How much weight will I lose with prescription weight loss medication?
Clinical trials show average weight loss of 5–21% of body weight depending on the medication and dose, alongside diet and exercise. Individual results vary significantly — some people lose more, others less. Weight loss typically occurs over several months. Your prescriber will give personalised expectations based on your health profile.
Are weight loss injections safe?
UK-licensed weight loss medications have undergone rigorous clinical trials and are approved by the MHRA. Common side effects include nausea and stomach discomfort, usually mild and temporary. Serious side effects are rare. Always discuss medical history and current medications with your prescriber before starting any weight loss medicine.
What happens when I stop taking weight loss medication?
Weight loss results are typically maintained through ongoing lifestyle changes — diet, physical activity, and behaviour change. Weight regain can occur if healthy habits are not sustained after stopping medication. Your healthcare team will support you in maintaining progress through continued healthy choices and monitoring.
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.