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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Mounjaro Weight Loss By Week — What To Expect In The UK
Mounjaro (tirzepatide) is a once-weekly injection that may help support weight loss when combined with lifestyle changes. Weight loss typically begins within the first 2–4 weeks of starting treatment, though results vary significantly between individuals. This guide covers realistic weekly weight loss expectations, how Mounjaro costs in the UK, and how to access it through NHS and private routes. Use our free GLP-1 weight loss calculator to estimate potential outcomes at different doses, and our BMI calculator to track your starting point.
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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.
Mounjaro Weekly Weight Loss & Access Routes In The UK
Weight loss with Mounjaro typically follows a gradual pattern rather than rapid results. During the first 4 weeks on the starting dose (2.5 mg), many people report nausea and appetite suppression before significant weight loss occurs. By weeks 5–8, as the body adjusts and doses escalate, meaningful weight reduction often becomes noticeable — averaging around 1–2 kg per week for many patients, though individual variation is substantial.
In the SURMOUNT-1 clinical trial, participants on 15 mg Mounjaro lost an average of 20.9% of body weight over 72 weeks. This translates to roughly 15–22 kg for a person starting at 100 kg, but results depend heavily on starting weight, diet adherence, physical activity, and individual metabolism.
- Weeks 1–4: Dose initiation (2.5 mg) — appetite changes begin, minimal weight loss typical
- Weeks 5–12: Dose escalation to 5–7.5 mg — noticeable weight loss often begins
- Weeks 13+: Maintenance phase — steady weight loss continues as doses reach therapeutic levels
Access in the UK is through two main routes: NHS specialist weight management services (which may involve waiting lists) or private online prescription following a clinical assessment. Neither route assures specific outcomes — weight loss remains dependent on your individual adherence to reduced-calorie diet and increased physical activity alongside the medication.
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.
UK Cost & How To Access Mounjaro Privately vs NHS
NHS Access: Mounjaro is available through NICE-approved specialist tier 3 and tier 4 weight management services. You'll need a GP referral and assessment by a multidisciplinary team. Availability and waiting times vary significantly by region (ICB). Once prescribed, you pay standard NHS prescription costs (currently £9.90 per item in England for those not exempt).
Private Access: Available through GPhC-registered online prescribing services. Costs typically range from £129–£320 per month depending on dose, with higher doses costing more. The private route requires an online consultation with a UK-licensed prescriber who will assess your suitability — no NHS referral needed. Private prescriptions are dispensed by regulated UK pharmacies.
What to expect: Whether NHS or private, your prescriber will start you on 2.5 mg and increase gradually over 16+ weeks. You'll self-inject once weekly using a KwikPen. Track your progress with our free progress tracker, and use our BMI calculator regularly to monitor changes in your health metrics.
- 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 much weight can you realistically lose with Mounjaro per week?
Weight loss varies significantly, but clinical trials show an average of 0.25–0.5 kg per week initially, increasing to 1–2 kg per week as doses escalate. By 72 weeks at maximum dose, average loss was around 20.9% of body weight — roughly 0.28 kg per week on average. Individual results depend on starting weight, diet, exercise, and metabolism. Your GLP-1 weight loss calculator can estimate your personal projection.
What's the difference between NHS and private Mounjaro in the UK?
NHS access requires GP referral to a specialist weight management service, involves a clinical assessment, and may have long waiting lists. Once prescribed, you pay standard NHS prescription fees. Private access is faster — you can access a prescription through an online clinical assessment with a UK-licensed prescriber without NHS referral. Private costs £129–£320 monthly depending on dose.
Is Mounjaro weight loss assured?
No. Mounjaro may help support weight loss, but individual results vary considerably. Clinical trials showed an average loss of 20.9% at maximum dose, but some people lose more and others less. Weight loss also requires a reduced-calorie diet and increased physical activity. A prescriber will assess whether Mounjaro is suitable for you based on your individual health.
Can I get Mounjaro on the NHS quickly?
NHS access depends on your regional ICB and specialist service capacity. Many areas have waiting lists of several months. If you have a BMI of 30+ (or 27.5+ with weight-related health conditions), ask your GP for a referral to tier 3 weight management services. Waiting times vary significantly by area. Private prescription routes are typically faster if available to you.
What's the difference between Mounjaro and Wegovy weight loss timelines?
Both are once-weekly injections with similar mechanisms (though Mounjaro is a dual GIP/GLP-1 agonist, Wegovy is GLP-1 only). Clinical trial data suggests slightly higher average weight loss with Mounjaro (20.9% vs ~15% for Wegovy), but this varies by individual. Timeline to results is similar — gradual over weeks 5–12, with meaningful loss by 3–4 months on higher doses.
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.