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 Programs with Prescription Medication in the UK
A weight loss program that includes prescription medication may help eligible UK adults manage their weight more effectively. The NHS and private prescribers now offer several licensed options, including GLP-1 receptor agonists like Mounjaro and Wegovy. These medications work alongside dietary changes and increased physical activity to support sustainable weight management. Eligibility depends on your BMI and individual health circumstances, and any prescription requires a clinical assessment from a qualified healthcare professional.
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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 Management Options
Three prescription weight loss 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. Clinical trials showed participants lost an average of 15–21% of their body weight over 72 weeks, though individual results vary significantly.
- Wegovy (semaglutide) — a GLP-1 receptor agonist injected once weekly. In clinical trials, participants achieved average weight loss of around 15% of their body weight, alongside a reduced-calorie diet and increased physical activity.
- Saxenda (liraglutide) — a daily GLP-1 injection, typically used when weekly injections are not suitable.
All three are prescription-only medicines requiring assessment by a UK-licensed prescriber. Eligibility generally applies to 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 cardiovascular disease. For people of South Asian, Chinese, Black African, or Black Caribbean heritage, lower BMI thresholds may apply due to higher health risks at lower weights.
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.
Accessing Weight Loss Medication: NHS vs Private
NHS access is available through specialist tier 3 weight management services, typically requiring a GP referral. However, NHS availability varies considerably by region, and waiting lists can be lengthy in many areas. Your GP can tell you whether your local integrated care board (ICB) offers these services and what the waiting time might be.
Private prescribing is available through GPhC-registered online pharmacies and prescribers without requiring an NHS referral. Following an online clinical assessment, a UK-licensed prescriber can issue a prescription if the medication is clinically appropriate for you. Start by speaking with your GP about your weight management goals — they can provide personalised advice, assess your BMI using our free BMI calculator, and discuss whether prescription medication might be suitable alongside lifestyle changes. Use our GLP-1 weight loss calculator to explore potential outcomes at different medication doses.
Before starting any weight loss program, calculate your current BMI and discuss your health history with a healthcare professional. Many people combine prescription medication with the support of a dietitian, and tracking your progress using our free progress tracker can help you stay motivated and accountable.
- 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) is a GLP-1 agonist only. Mounjaro has two mechanisms of action, and in trials showed slightly higher average weight loss (15–21% vs approximately 15% for Wegovy). Both are once-weekly injections. Individual results vary, and suitability depends on your personal health profile, assessed by your prescriber.
Am I eligible for prescription weight loss medication on the NHS?
Generally, 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. Lower thresholds apply for some ethnic backgrounds. Eligibility is assessed individually by a specialist weight management service. Ask your GP for a referral to your local tier 3 service.
How quickly will I lose weight with these medications?
Clinical trials showed average weight loss of 15–21% over several months to a year, depending on the medication and dose. However, individual results vary significantly. Weight loss medications work best alongside a reduced-calorie diet and increased physical activity. Sustainable loss typically occurs at 0.5–1 kg per week.
Can I get prescription weight loss medication privately without waiting for the NHS?
Yes. Private UK-licensed prescribers can assess and prescribe weight loss medication following an online clinical assessment, without an NHS referral. This is available through GPhC-registered pharmacies. Costs vary by medication, dose, and provider, typically ranging from £129–£320+ per month. Always ensure you use a legitimate, regulated prescriber.
What happens if I stop taking the medication?
Weight loss effects may reverse if the medication is stopped and lifestyle changes are not maintained. These medications are tools to support sustained weight management, not permanent solutions. Long-term success depends on continuing healthy eating and physical activity habits. Your prescriber will discuss this with you before you start.
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.