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
When do people notice weight loss on medication?
Weight loss timelines vary depending on the medication, dose, and individual factors—but most people using prescription weight management medication in the UK start noticing changes within 2 to 4 weeks. Understanding what to expect, and when, helps set realistic goals and maintain motivation. This guide covers the evidence on GLP-1 medications like Mounjaro and Wegovy, NHS eligibility, and how to track your progress accurately.
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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 medications and timelines
Three prescription-only medications are licensed in the UK for weight management: Mounjaro (tirzepatide), Wegovy (semaglutide), and Saxenda (liraglutide). Most people report noticing appetite reduction and feeling fuller after smaller meals within the first 1–2 weeks, though visible weight loss typically appears after 2–4 weeks of consistent use. Clinical trials show average weight loss of 15–21% over several months with Mounjaro and approximately 15% with Wegovy, alongside a reduced-calorie diet and increased physical activity. Individual results vary significantly depending on starting weight, metabolism, adherence to lifestyle changes, and dose. Appetite suppression usually happens first; visible weight changes follow. Early doses may cause mild digestive side effects like nausea or constipation—these often improve within days to weeks. You can track progress using our GLP-1 weight loss calculator to estimate potential outcomes, and monitor changes with our free progress tracker to stay motivated throughout your journey.
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.
Accessing weight loss medication through NHS or private routes
In the UK, prescription weight loss medication is available through two routes: NHS specialist services (via referral from your GP to a tier 3 or tier 4 weight management service) or private prescribing through registered online providers following a clinical assessment. NHS access requires a BMI of 30 or above, or 27–29.9 with weight-related health conditions such as type 2 diabetes or high blood pressure. Private routes are faster but involve costs. Both require a licensed prescriber to assess your individual eligibility and suitability. If you're eligible, you'll typically notice appetite changes within days and measurable weight loss within 2–4 weeks. Use our free BMI calculator to check where you stand, then speak to your GP about available options in your area. Discuss timelines and realistic expectations during your consultation.
- 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 soon will I see weight loss on Mounjaro or Wegovy?
Most people notice appetite suppression within 1–2 weeks, but visible weight loss typically appears after 2–4 weeks of consistent use alongside a reduced-calorie diet and physical activity. Clinical trials show average weight loss of 15–21% over several months, though individual results vary. Early doses may cause temporary digestive side effects.
Does nausea mean the medication is working?
Not necessarily. Nausea is a common side effect, especially in the first few weeks, and usually improves as your body adjusts. It's separate from appetite suppression—you may feel nauseous and still have reduced hunger. If nausea persists beyond a few weeks, contact your prescriber.
Can I speed up weight loss with these medications?
Results depend on medication adherence, calorie deficit, and lifestyle changes—not the medication alone. The NHS recommends losing 0.5–1 kg per week for sustainable results. Faster weight loss may lead to muscle loss and nutrient deficiency. Always follow your prescriber's guidance and maintain consistent dietary and exercise habits.
What if I don't notice weight loss in the first month?
Weight loss timelines vary by individual. Some people see changes within 2 weeks; others take 4–6 weeks. Ensure you're maintaining a consistent calorie deficit, staying hydrated, and taking the medication as prescribed. If you have no changes after 6 weeks, discuss this with your prescriber—dose adjustments may be needed.
How do I track weight loss progress accurately?
Weigh yourself weekly (same day, same time, without clothes) and record results. Use our free progress tracker to log your journey visually. Also track non-scale changes: energy levels, clothes fit, waist circumference, and how you feel. This provides a fuller picture of progress beyond the scales alone. ```
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.