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 Long Does Mounjaro Take To Work — And What It Costs in the UK
Mounjaro (tirzepatide) typically begins reducing appetite within days, though noticeable weight loss usually takes 4–8 weeks to become apparent. Most people start seeing consistent results by weeks 8–12 as their body adjusts to the medication. The timeframe depends on your individual response, diet, physical activity, and which dose you're taking. This guide explains how Mounjaro works, when to expect results, and the cost and access routes available to UK adults seeking this prescription weight loss injection.
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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.
Timeline: When Does Mounjaro Start Working?
Mounjaro is a dual GIP receptor and GLP-1 receptor agonist that works by mimicking natural hormones to regulate appetite and support feeling fuller after meals. Most people notice changes within the first few days — typically reduced hunger, less interest in food, and smaller appetite. However, this is different from visible weight loss.
- Weeks 1–4 (starting dose 2.5 mg): Appetite suppression begins; weight loss may be minimal (0–1 kg average)
- Weeks 5–8 (dose escalation to 5 mg): More noticeable appetite control; weight loss accelerates (approximately 1–2 kg per week)
- Weeks 9–16 (doses 7.5–10 mg): Consistent weight loss continues; results become visually apparent for most people
- Week 17+ (maintenance doses up to 15 mg): Weight loss plateaus as body reaches a new equilibrium; ongoing loss slower but sustainable
Individual results vary significantly based on starting weight, baseline metabolism, adherence to diet and exercise, and genetic factors. Some people see substantial loss by week 8; others see more gradual progress over 12 weeks.
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.
Cost and Access Routes in the UK
Accessing Mounjaro in the UK depends on your chosen route. NHS access is typically through specialist tier 3 weight management services following a GP referral, though availability and waiting times vary significantly by region. Private prescription access involves an online consultation with a UK-licensed prescriber, followed by dispensing through a GPhC-registered pharmacy. Private costs range from approximately £130–£280 per month depending on your dose, with 2.5 mg being the lowest cost and 15 mg the highest. Each KwikPen contains 4 weekly injections. Use our GLP-1 weight loss calculator to estimate potential results at different doses, and track your progress with our free progress tracker once you start treatment.
- 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 noticeable by weeks 4–8, with average loss of 0.5–2 kg per week during dose escalation. Clinical trials showed average loss of 15–21% of body weight over 72 weeks on higher doses. Results vary; some people lose faster, others more gradually. Combine Mounjaro with a reduced-calorie diet and physical activity for best outcomes.
Does Mounjaro work better than Wegovy?
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist, while Wegovy (semaglutide) is GLP-1 only. Clinical trials suggest tirzepatide may produce slightly greater average weight loss, but individual results vary significantly. Neither is universally "better" — it depends on your personal response and medical history.
How much does Mounjaro cost privately in the UK?
Private Mounjaro costs typically range from £130–£280 per month depending on dose. Starting dose (2.5 mg) is cheapest; maximum dose (15 mg) is most expensive. Prices vary slightly between providers. Each KwikPen is a 4-week supply. NHS access may be available through specialist services but involves regional waiting lists.
Can I get Mounjaro on the NHS?
Yes, Mounjaro is available through NHS specialist weight management services for eligible adults. You'll need a GP referral to tier 3 services. Availability, eligibility criteria, and waiting times vary significantly by region and integrated care board (ICB). Some areas have shorter waits; others may have waiting lists of several months.
What happens if I stop taking Mounjaro?
Weight may be regained if diet and exercise habits don't change. Mounjaro is not a permanent solution — it's a tool to support weight loss alongside lifestyle changes. Your prescriber will advise on duration of treatment based on your individual health, progress, and response to the medication. ```
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.