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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How Long Does Weight Loss Take with UK Medication?
Estimating how long weight loss will take depends on several factors, including your starting weight, chosen approach, and whether you use prescription medication. In the UK, several prescription-only weight management options are available for eligible adults. This guide explains how to estimate your personal weight loss timeline, which medication options exist, and how to find out if you qualify for NHS or private weight loss treatment.
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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 main prescription medications are licensed in the UK for weight management: Mounjaro (tirzepatide), Wegovy (semaglutide), and Saxenda (liraglutide). Clinical trials show these medications can support weight loss alongside reduced-calorie diet and increased physical activity.
- Mounjaro: Dual GIP/GLP-1 agonist. Average weight loss in trials was approximately 15–21% of body weight over 72 weeks at maximum dose (15 mg weekly).
- Wegovy: GLP-1 agonist. Average weight loss in trials was approximately 15% of body weight over 68 weeks at maximum dose (2.4 mg weekly).
- Saxenda: GLP-1 agonist given daily. Less commonly prescribed than Mounjaro or Wegovy but still licensed and available.
Individual results vary significantly. Your personal weight loss timeline depends on which medication you use, your dose, how your body responds, and your commitment to lifestyle changes. Use our GLP-1 weight loss calculator to 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.
Eligibility and How to Access Weight Loss Medication
In the UK, you may be eligible for prescription weight loss medication if you have a BMI of 30 or above, or BMI of 27–29.9 with a weight-related health condition such as type 2 diabetes, high blood pressure, or cardiovascular disease. For adults of South Asian, Chinese, Black African, or Black Caribbean heritage, lower BMI thresholds apply (27.5+).
Access is available through two routes: NHS specialist weight management services (via GP referral, though waiting lists can be long and availability varies by region) or private online prescribing (following a clinical assessment with a UK-licensed prescriber). Your GP can advise on NHS eligibility and local services, or you can explore private options. Calculate your BMI using our free BMI calculator to check where you stand.
- 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.
How quickly will I lose weight on Mounjaro or Wegovy?
Weight loss typically begins within the first 2–4 weeks of starting treatment, though some people see results within 1–2 weeks. Most significant losses occur between weeks 8–20 as your dose increases. Clinical trials show an average of 15–clinically studied weight loss over 72 weeks with Mounjaro and approximately 15% over 68 weeks with Wegovy, but individual results vary considerably based on adherence, diet, exercise, and metabolism.
What's the difference between NHS and private weight loss medication access?
NHS access is through specialist tier 3 weight management services via GP referral—it's free but availability varies significantly by region and waiting lists can be months or years. Private access is through UK-licensed prescribers via online consultation—faster access and no NHS referral needed, but you pay for the medication (typically £129–£320 per month depending on dose). Both routes require a clinical assessment to confirm suitability.
Can I estimate my personal weight loss timeline?
Yes. A rough estimate is possible: if you lose 0.5–1 kg per week (a safe rate) and need to lose 20 kg, that's approximately 5–10 months. However, with GLP-1 medications, initial weight loss may be faster, then plateau. Our GLP-1 weight loss calculator provides a personalised projection based on your current weight, height, age, and chosen dose—use it alongside our progress tracker to monitor actual results.
Do I need to change my diet and exercise if I take weight loss medication?
Yes. Prescription weight loss medications work most effectively alongside a reduced-calorie diet and increased physical activity. Clinical trials that showed 15–clinically studied weight loss included structured dietary support and exercise guidance. Medication alone is not effective—lifestyle changes are essential for both weight loss success and maintaining results long-term after stopping treatment.
How do I know if I'm eligible for prescription weight loss medication?
Check your BMI using our free BMI calculator. If your BMI is 30 or above, or 27–29.9 with a weight-related health condition, you may be eligible. Your next step is to speak with your GP about NHS specialist weight management services, or contact a private online prescriber for a clinical assessment. They will review your full health history, medications, and medical conditions to confirm suitability.
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.