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
Where Do You See Weight Loss First?
Weight loss typically shows first in areas where your body stores fat most readily, though this varies significantly between individuals. For most people, the face, chest, and upper body tend to slim down first, whilst stubborn areas like the belly, hips, and thighs often take longer. Understanding how your body loses weight can help you stay motivated during your weight management journey. If you're considering prescription weight loss medication available in the UK—such as Mounjaro, Wegovy, or other GLP-1 options—knowing what to expect can make the process feel more achievable.
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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 Prescription Weight Management Options
If you're eligible, prescription weight loss medications may help support your weight management journey alongside diet and physical activity. The main UK-licensed options are:
- Mounjaro (tirzepatide) — a dual GIP and GLP-1 receptor agonist, given as a once-weekly injection starting at 2.5 mg, escalating to a maximum of 15 mg. Clinical trials showed participants lost an average of 15–21% of their body weight at higher doses.
- Wegovy (semaglutide) — a GLP-1 receptor agonist, once-weekly injection up to 2.4 mg. Clinical trial data showed average weight loss of approximately 15% of body weight.
- Saxenda (liraglutide) — a GLP-1 receptor agonist given as a daily injection up to 3 mg.
All three are prescription-only and require a clinical assessment before being prescribed. Eligibility typically includes adults with a BMI of 30 or above, or 27 or above with weight-related health conditions like type 2 diabetes or high blood pressure. Individual results vary significantly. Try our free GLP-1 weight loss calculator to explore 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.
Getting Started: NHS vs Private Access in the UK
You can access prescription weight loss medication through two main routes in the UK. NHS access is through specialist tier 3 weight management services—you'll need a GP referral, though availability and waiting times vary significantly by region. Private access is available through GPhC-registered online pharmacies following an online clinical assessment; you don't need an NHS referral and can typically start within days.
Your GP is the best starting point. They can assess your overall health, discuss your weight management goals, and advise whether prescription medication might be suitable for you. They can also explain the NHS pathway in your area. Use our free BMI calculator to understand your current status before your appointment—this gives you a clear baseline for that conversation.
- 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.
Does weight loss show in the face first?
For many people, yes—the face often slims down relatively early in weight loss because facial fat is mobilised readily. However, this varies by genetics, age, and individual metabolism. Some people notice changes in the face and neck first, whilst others see changes in the waist and upper body before facial changes become noticeable.
Can prescription weight loss medication help me lose weight faster?
Prescription medications like Mounjaro and Wegovy may help support weight loss by reducing appetite and supporting feeling fuller after meals. Clinical trials showed average weight loss of 15–21% body weight. However, they work best alongside a reduced-calorie diet and increased physical activity. Results vary significantly between individuals, and individual results cannot be assured.
How do I know if I'm eligible for weight loss medication in the UK?
General eligibility includes a BMI of 30 or above, or 27 or above with weight-related health conditions (diabetes, high blood pressure, sleep apnoea, cardiovascular disease). Your GP or a licensed prescriber can assess your individual circumstances. 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.
How long does it take to see weight loss results with GLP-1 medication?
Many people notice initial results within the first 2–4 weeks, though this varies. Steady, sustainable weight loss typically continues over 12–16 weeks as doses are increased. The full benefit is usually assessed after 12–16 weeks of treatment. Using our free progress tracker can help you log changes and stay motivated throughout your journey.
What's the difference between Mounjaro and Wegovy for weight loss?
Mounjaro (tirzepatide) is a dual GIP and GLP-1 agonist that may produce slightly higher average weight loss (15–21%) than Wegovy (semaglutide), a single GLP-1 agonist (approximately 15% average). Both are once-weekly injections, but Mounjaro has higher maximum doses. Individual response varies, and your prescriber will recommend what's most suitable for you based on your health profile.
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.