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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Prescription Meds for Weight Loss in the UK
If you're looking for prescription weight loss medication in the UK, there are now several licensed options available to help support sustainable weight management. These medications work alongside diet and exercise changes and may help reduce appetite and support weight loss. Access varies between NHS specialist services and private prescribing. This guide covers the main prescription weight loss meds available to UK adults and how to find out if you're eligible.
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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 for weight management in the UK: Mounjaro (tirzepatide), Wegovy (semaglutide), and Saxenda (liraglutide). All three are GLP-1 or dual GIP/GLP-1 receptor agonists that work by reducing appetite and helping you feel fuller after eating.
- Mounjaro — a once-weekly dual GIP and GLP-1 injection. Clinical trials showed participants lost an average of 15–21% of their body weight over 72 weeks
- Wegovy — a once-weekly GLP-1 injection. STEP trial data showed average weight loss of approximately 15% of body weight
- Saxenda — a daily GLP-1 injection, with evidence supporting modest weight loss when combined with lifestyle changes
These are prescription-only medicines requiring clinical assessment before being prescribed. Individual results vary significantly, and weight loss is not assured. All require a reduced-calorie diet and increased physical activity for best results. You can check your BMI and explore projected weight loss with our free GLP-1 weight loss calculator to understand where you stand.
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 in the UK
In the UK, prescription weight loss medication is accessed through two routes. NHS access is through specialist tier 3 weight management services, typically requiring a GP referral. Waiting lists vary by region and can be lengthy in many areas. Private access is available through GPhC-registered online prescribers following a clinical assessment — no NHS referral required.
To find out if you're eligible, speak to your GP about your weight management goals and health. Eligibility for adults typically requires a BMI of 30 or above, or 27–29.9 with weight-related health conditions like type 2 diabetes, high blood pressure, or cardiovascular disease. South Asian, Chinese, Black African, and Black Caribbean adults may have access at lower BMI thresholds due to increased health risks at those levels.
- 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.
Who is eligible for prescription weight loss medication in the UK?
Generally, adults with a BMI of 30 or above, or 27–29.9 with weight-related health conditions like type 2 diabetes, hypertension, or sleep apnoea. South Asian, Chinese, Black African, and Black Caribbean adults may be eligible from lower BMI levels. A GP or prescriber will assess your individual suitability.
How much weight can I expect to lose with these medications?
Clinical trials show average weight loss of 15–21% of body weight, but individual results vary significantly. Weight loss depends on the specific medication, dose, adherence, diet, and physical activity. These medicines are tools alongside lifestyle changes, not replacements for them.
What's the difference between NHS and private prescription routes?
NHS access is through specialist weight management services (typically longer waiting lists, free on prescription). Private access is through online prescribers without NHS referral (faster, but you pay for treatment). Both routes require a clinical assessment to confirm suitability.
Are these medications safe long-term?
These medications have been studied in clinical trials lasting up to 72 weeks. Long-term safety data continues to be gathered. They have known side effects, commonly nausea and digestive changes. Always discuss safety concerns with your GP or prescriber.
Can I use weight loss medication if I take other medications?
Some medications may interact with GLP-1 injectables — for example, oral contraceptives may have reduced absorption. Always inform your GP or prescriber of all medications you take. They will assess safety and may recommend adjustments to your treatment plan.
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.