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
How Quickly Does Mounjaro Take To Work in the UK?
Mounjaro (tirzepatide) doesn't work instantly — it takes time to build up in your system and show effects. Most people notice changes in appetite within the first 1–2 weeks, but meaningful weight loss typically becomes visible after 4–8 weeks of treatment. The timeline depends on your dose, diet, and how your body responds. If you're considering Mounjaro in the UK, understanding both the effectiveness timeline and how to access it through NHS or private prescription routes will help you make an informed decision.
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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.
How Long Does Mounjaro Take to Show Results — Timeline & Cost Context
Mounjaro works through dose titration — your dose increases gradually over weeks to allow your body to adjust and find the optimal level. Here's what to expect on the timeline:
- Weeks 1–4 (2.5 mg): Starting dose. Many people report reduced appetite and food cravings within days, though weight loss is typically minimal at this stage.
- Weeks 5–8 (5 mg): First escalation. More noticeable appetite suppression and early weight loss may become visible on scales.
- Weeks 9–16 (7.5–10 mg): Further escalation. Weight loss momentum typically builds. Clinical trials show average loss of 5–8% of body weight by week 12.
- Weeks 17+ (12.5–15 mg): Maintenance doses. Maximum effect typically reached by week 20. SURMOUNT trial data shows average weight loss of 15–21% of body weight at 72 weeks on Mounjaro.
Individual results vary significantly. Some people see rapid changes; others experience slower progress. Combining Mounjaro with a reduced-calorie diet and increased physical activity produces better results than medication alone.
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 Mounjaro in the UK — NHS vs Private Cost & Timeline
NHS access: Limited availability. NICE has approved tirzepatide for NHS specialist tier 3 weight management services, but access varies dramatically by region and ICB. NHS waiting lists can be months to years long, and you'll need a GP referral to specialist services. Private prescription access: Faster and more flexible. A UK-licensed prescriber conducts an online clinical assessment (usually 15–20 minutes). If approved, your prescription is sent to a GPhC-registered pharmacy. Costs range from approximately £129–£320 per month depending on dose — higher doses cost more. Private access requires no NHS referral. Try our GLP-1 weight loss calculator to estimate potential results at different Mounjaro doses and understand whether the investment aligns with your goals.
- 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?
Weight loss typically becomes visible after 4–8 weeks. Clinical trials showed average weight loss of 5–8% by week 12 and 15–21% by week 72. However, individual results vary. Diet, exercise, starting weight, and how your body responds all affect speed. Track your progress with our free progress tracker to monitor changes beyond just the scales.
Does Mounjaro work better than Wegovy in the UK?
Mounjaro and Wegovy use different mechanisms — Mounjaro is a dual GIP and GLP-1 agonist; Wegovy is GLP-1 only. Clinical trials show Mounjaro produced slightly higher average weight loss (15–21% vs 15% for Wegovy), but individual response varies. Your prescriber will recommend based on your personal health profile and medical history.
What's the cost difference between NHS and private Mounjaro?
NHS access is free (if available through your local ICB and specialist service) but involves long waiting lists. Private prescriptions cost £129–£320 per month depending on dose. Doses range from 2.5 mg to 15 mg — higher doses cost more. Check your local NHS pathway first, but private access is significantly faster.
How do I get a Mounjaro prescription in the UK privately?
Book an online consultation with a UK-licensed prescriber. The assessment takes 15–20 minutes and reviews your medical history, BMI, and weight-related health conditions. If approved, your prescription is issued and sent to a GPhC-registered pharmacy for dispensing. No NHS referral needed.
Can I use our BMI calculator to check if I'm eligible for Mounjaro?
Yes. Our free BMI calculator shows your BMI instantly. UK eligibility typically requires BMI ≥30, or BMI ≥27 with weight-related health conditions like diabetes or hypertension. South Asian, Black African, or Black Caribbean adults may have lower thresholds. Use the calculator to check your starting point, then discuss eligibility with your GP or prescriber.
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.