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
Fast Weight Loss Products in the UK
When you're looking to lose weight quickly, you'll find various fast weight loss products available in the UK — but not all deliver sustainable results. The most effective options combine lifestyle changes with evidence-based approaches. Prescription weight loss medications, approved by the NHS and MHRA, can support weight management when used alongside a reduced-calorie diet and increased physical activity. This guide explains what actually works, how to access prescription weight loss treatment on the NHS, and what the clinical evidence shows about gradual weight management.
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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.
Prescription Weight Loss Medications — What the Evidence Shows
Prescription weight loss medications are the most clinically proven fast weight loss products available in the UK. Unlike unregulated supplements or fad diet products, these medicines undergo rigorous testing and are monitored by the MHRA.
GLP-1 receptor agonist injections are currently the most effective prescription option for weight management. Wegovy (semaglutide) and Mounjaro (tirzepatide) are both once-weekly injections licensed for weight loss in UK adults. The STEP-1 clinical trial showed that Wegovy helped participants lose an average of 14.9% of their body weight over 68 weeks — significantly more than diet alone. Mounjaro, a dual GIP and GLP-1 medication, demonstrated even greater results in clinical trials, with average weight loss of 15–21% of body weight depending on dose.
These medications work by activating hormone pathways that reduce appetite, increase fullness, and help regulate food intake. They're prescription-only and require a clinical assessment to ensure suitability. Access through the NHS varies by region and typically involves referral to a specialist weight management service, though private prescribing via UK-licensed online prescribers is also available.
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 Weight Loss Support and Other Evidence-Based Approaches
The NHS weight loss pathway offers structured support at multiple levels. Your GP can initially help with lifestyle advice, calorie-counted diet plans, and referral to community weight management programmes. For more intensive support, specialist tier 3 services can prescribe weight loss medications like Mounjaro or Wegovy where appropriate. Using our free BMI calculator above can help you understand your current health category and discuss options with your GP.
Other effective fast weight loss approaches include low-calorie structured diets (under medical supervision), intermittent fasting, and very low-calorie diets (VLCDs) — though these require professional guidance. The NHS recommends losing 0.5–1 kg per week for sustainable results. Track your progress with our free progress tracker to stay motivated and identify what works best for you.
- 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 are the fastest weight loss products available on prescription in the UK?
Wegovy (semaglutide) and Mounjaro (tirzepatide) are the fastest-acting prescription weight loss products currently licensed in the UK. Both are once-weekly injections. Clinical trials show Wegovy assists average weight loss of around 15% of body weight, whilst Mounjaro showed 15–21% average weight loss. Both require prescription and clinical assessment. Results vary individually and are achieved alongside diet and exercise changes.
Can I get prescription weight loss medication through the NHS?
Yes, prescription weight loss medications are available through NHS specialist tier 3 weight management services, though availability varies significantly by region and local ICB commissioning. You'll need referral from your GP. Waiting times can be lengthy in many areas. Private online prescribing through UK-licensed prescribers is an alternative route if you meet clinical eligibility criteria (typically BMI 30+ or 27+ with weight-related health conditions).
Are there fast weight loss products I can buy without a prescription?
Many unregulated supplements and diet products claim fast weight loss but lack clinical evidence. Structured, lower-calorie diet programmes and apps can support weight loss, but prescription medications have the strongest clinical backing. The NHS recommends discussing any weight loss product with your GP first to ensure safety and suitability. Our free weight loss calculator can help you estimate potential results with evidence-based approaches.
How do prescription weight loss injections like Mounjaro work?
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist — it activates two natural hormone pathways to reduce appetite, increase feelings of fullness, and help regulate food intake. Wegovy (semaglutide) works via GLP-1 activation alone. Both slow how quickly food leaves your stomach and help regulate blood sugar. They're most effective when combined with reduced-calorie diet and physical activity increases.
What's the difference between fast weight loss and sustainable weight loss?
Fast weight loss often involves rapid calorie restriction or unproven products, which can lead to muscle loss and rebound weight gain. Sustainable weight loss (0.5–1 kg per week) preserves muscle, is easier to maintain long-term, and delivers better health outcomes. Prescription medications support sustainable loss by addressing appetite regulation, not just cutting calories drastically. Use our BMI calculator and progress tracker to monitor healthy, steady progress.
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.