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 Medication Available in the UK
Despite the term "nonprescription weight loss," the most effective medical options for weight management in the UK actually require a prescription. Three licensed medications are available: Mounjaro (tirzepatide), Wegovy (semaglutide), and Saxenda (liraglutide). These are prescription-only medicines available through both NHS specialist services and private prescribing. This guide explains eligibility criteria, how they work, and how to access them. Use our free BMI calculator above to check whether you might be eligible for prescription weight loss support.
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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 Prescription Weight Loss Medications
Mounjaro (tirzepatide) is a once-weekly injection that works as a dual GIP and GLP-1 receptor agonist. In clinical trials, it helped participants lose an average of 15–21% of their body weight alongside a reduced-calorie diet and increased physical activity. Wegovy (semaglutide) is a once-weekly GLP-1 receptor agonist injection with an average weight loss of around 15% in trials. Saxenda (liraglutide) is a daily GLP-1 injection, less commonly prescribed than the weekly options.
You may be eligible if you have 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. Adults of South Asian, Chinese, Black African, or Black Caribbean heritage may qualify at slightly lower BMI thresholds due to higher health risks at lower weights. All three are prescription-only medicines requiring a clinical assessment before being prescribed. Individual results vary significantly—these figures are clinical trial averages, not assured outcomes.
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 Medication in the UK
NHS access is through specialist tier 3 or tier 4 weight management services. Your GP can refer you if you meet eligibility criteria, though waiting lists vary significantly by region and can be lengthy in many areas. Private access is available through UK-licensed prescribers following an online clinical assessment with a GPhC-registered pharmacy. This typically does not require an NHS referral and offers faster access, though at a cost of approximately £130–£320 per month depending on the dose.
Start by speaking with your GP about weight management options. Use our free weight loss calculator to estimate potential outcomes at different doses, and our weight converter to track your progress in whichever measurement you prefer. Your prescriber will assess whether medication is suitable based on your individual health history and current medications.
- 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 is the difference between Mounjaro and Wegovy?
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist, while Wegovy (semaglutide) activates only GLP-1. Clinical trials showed Mounjaro produced slightly higher average weight loss (15–21% vs 15%), but individual results vary. Both are once-weekly injections. The choice depends on prescriber assessment, availability, and your personal health profile.
Am I eligible for prescription weight loss medication on the NHS?
You may be eligible if you have a BMI of 30 or above, or 27 or above with weight-related health conditions like type 2 diabetes or high blood pressure. South Asian, Chinese, Black African, or Black Caribbean adults may qualify at lower BMI thresholds. Your GP can assess your eligibility and refer you to a specialist weight management service.
How much weight will I lose on weight loss medication?
Clinical trials show average losses of 15–21% of body weight, but individual results vary significantly. Weight loss depends on the medication, dose, your adherence to the treatment, dietary changes, and physical activity. A prescriber can discuss realistic expectations for your situation. Our GLP-1 weight loss calculator can help estimate potential outcomes.
Can I get weight loss medication privately if the NHS waiting list is too long?
Yes. Private prescribing through UK-licensed providers is available without an NHS referral. Following an online clinical assessment, a prescription can be issued and dispensed by a GPhC-registered pharmacy. Costs typically range from £130–£320 per month depending on the dose and provider.
Are there side effects I should know about?
Common side effects include nausea, diarrhoea, constipation, and stomach pain, particularly in the first weeks. Most side effects are manageable and often reduce over time as the body adjusts. Serious side effects are rare but can include pancreatitis or gallbladder issues. Your prescriber will discuss all risks and benefits during your assessment.
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.