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 Diets and Medication in the UK
Weight loss diets are one approach to managing your weight, but prescription medication can offer additional support for eligible adults in the UK. If you're exploring weight management options beyond diet and exercise, understanding what's available through the NHS and privately is essential. This guide covers UK-licensed prescription weight loss options, eligibility criteria, and how to have a conversation with your GP about the right approach for you.
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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 Options
Three prescription medications are currently licensed for weight management in the UK: Mounjaro (tirzepatide), Wegovy (semaglutide), and Saxenda (liraglutide). Mounjaro and Wegovy are once-weekly injections, while Saxenda is a daily injection. All three work by mimicking natural hormones that regulate appetite and blood sugar.
Clinical evidence shows that these medications, used alongside reduced-calorie diet and increased physical activity, can help eligible adults lose weight. In clinical trials, Mounjaro helped participants lose an average of 15–21% of their body weight, while Wegovy showed average losses of around 15% over 68 weeks. Results vary between individuals, and medications are most effective when combined with lifestyle changes.
To be eligible for prescription weight loss medication in the UK, you typically need a BMI of 30 or above, or a BMI of 27–29.9 with weight-related health conditions such as type 2 diabetes, high blood pressure, or sleep apnoea. Lower BMI thresholds may apply if you have South Asian, Chinese, Black African, or Black Caribbean heritage. Use our free BMI calculator to check where you sit, and our GLP-1 weight loss calculator can help you estimate potential outcomes at different doses.
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 — How to Get Started
NHS access: Prescription weight loss medication is available through NHS specialist tier 3 weight management services. Your GP can refer you to your local service, though waiting lists vary significantly by region and can extend several months. Not all areas have immediate availability, and access depends on your local Integrated Care Board (ICB) capacity.
Private access: You can also access prescription weight loss medication through private online prescribing services, which offer faster access without NHS waiting lists. These services require an online consultation with a UK-licensed prescriber, who will assess your suitability before issuing a prescription dispensed by a GPhC-registered pharmacy.
The first step is speaking with your GP. They can assess whether weight management medication is appropriate for you, check your BMI and health history, and discuss whether NHS referral or private options suit your situation. Track your progress with our free progress tracker alongside whichever approach you choose.
- 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.
Are weight loss diets or medication more effective?
Both can work, and they're most effective together. Prescription medications like Mounjaro or Wegovy are designed to support dietary changes and exercise, not replace them. Evidence suggests combining medication with a reduced-calorie diet and physical activity produces the best results. Your GP can advise which approach is right for you.
What is the difference between Mounjaro and Wegovy?
Both are once-weekly injections, but they work slightly differently. Mounjaro is a dual GIP and GLP-1 agonist, while Wegovy is a GLP-1 agonist alone. Clinical trials showed Mounjaro may produce slightly higher average weight loss (15–21%) compared to Wegovy (around 15%), though individual results vary significantly. Your prescriber will recommend the most suitable option.
Am I eligible for weight loss medication on the NHS?
Generally, you're eligible if you have a BMI of 30 or above, or 27–29.9 with weight-related health conditions like type 2 diabetes or high blood pressure. Lower thresholds apply if you have certain ethnic backgrounds. Speak with your GP about referral to your local NHS weight management service to discuss eligibility and local availability.
How quickly will I lose weight on prescription medication?
Weight loss typically begins within the first 4 weeks but increases over several months as your dose is adjusted. Clinical trials show most weight loss occurs between weeks 8 and 52. The NHS recommends losing 0.5–1 kg per week as a healthy, sustainable rate. Individual results vary, and medications work best with dietary and lifestyle changes.
What happens if I stop taking weight loss medication?
Weight regain is common after stopping medication, particularly if diet and exercise habits aren't maintained. This is why long-term lifestyle changes are crucial. Some people continue medication indefinitely, while others use it as a temporary support tool. Your prescriber will discuss the best duration and approach for your individual situation.
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.