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
Free tracker included with every download this week
Fastest Weight Loss Diet: UK Prescription Options
When seeking the fastest weight loss results, prescription medication may be an option if you're eligible. In the UK, licensed weight management injections are now available through the NHS and private prescribing services. These medications work alongside diet and exercise changes—not instead of them—to support faster, sustainable weight loss. Understanding your options and eligibility is the first step toward effective weight management. Use our free BMI calculator to check where you currently stand, and explore whether prescription support might be right 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 Weight Management Medication Options
Three prescription-only medications are licensed in the UK for weight management alongside lifestyle changes. Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist injected once weekly, with clinical trial results showing average weight loss of 15–21% of body weight over 72 weeks. Wegovy (semaglutide) is a GLP-1 receptor agonist, also once weekly, with STEP trial data showing approximately clinically studied weight loss. Saxenda (liraglutide) is a daily GLP-1 injection, typically prescribed when once-weekly options aren't suitable. All three require a prescription following clinical assessment. Eligibility requires a BMI of 30 or above, or 27 or above with weight-related health conditions such as type 2 diabetes, hypertension, or cardiovascular disease. Your prescriber will assess whether you're suitable based on your individual health, medical history, and current medications.
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 Weight Loss Medication in the UK
NHS access is through tier 3 specialist weight management services via GP referral, though availability varies significantly by region and waiting lists can be lengthy. Private access is available through GPhC-registered online prescribing services following a clinical consultation—faster but at personal cost (typically £129–£320 monthly depending on dose). Both require a consultation with a licensed prescriber who will assess your suitability. Neither route assures weight loss; results vary based on adherence to medication, diet, and physical activity. Speak with your GP about the best weight loss UK pathway for your circumstances, whether NHS or private.
- 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 fastest safe rate of weight loss?
The NHS recommends losing 0.5–1kg (1–2lbs) per week for sustainable results. Faster loss is possible with medical support but increases muscle loss risk. Even a clinically studied weight loss delivers significant health benefits including improved blood sugar control and reduced blood pressure.
Am I eligible for prescription weight loss medication in the UK?
Generally, you're eligible if you have a BMI of 30 or above, or 27 or above with weight-related conditions like type 2 diabetes or high blood pressure. Your GP or a licensed prescriber will assess your individual eligibility following a consultation. South Asian, Chinese, Black African, and Black Caribbean adults may qualify at slightly lower BMI thresholds due to higher health risks.
How quickly do weight loss injections work?
Weight loss usually begins within 2–4 weeks, but most significant results appear after 8–12 weeks of consistent use. Maximum results are typically seen after 16–20 weeks. Speed depends on your starting weight, dose, diet adherence, and physical activity. Results vary significantly between individuals.
Do I need to change my diet if I take weight loss medication?
Yes. Prescription weight management medications are most effective alongside a reduced-calorie diet and increased physical activity. They support appetite reduction and help you feel fuller on smaller portions—but don't replace the need for healthier eating habits. Your prescriber or a dietitian can advise on the best dietary approach for you.
What happens after I stop taking weight loss medication?
Weight regain can occur if lifestyle changes aren't maintained. Most people benefit from ongoing support through weight management programmes, continued physical activity, and sustained dietary changes. Your GP or prescriber can discuss long-term weight maintenance strategies with you.
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.