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
Starting Mounjaro in Week 1 — UK Access & Cost Guide
If you've been prescribed Mounjaro, week 1 marks the beginning of your weight management journey with a 2.5mg starting dose. This guide explains how to access Mounjaro in the UK, whether through NHS specialist services or private online prescription, the typical costs involved, and what you can expect during that crucial first week. Understanding your options upfront helps you make an informed decision about which route suits your circumstances. Use our free GLP-1 weight loss calculator to explore potential outcomes as you begin 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.
How to Access Mounjaro in the UK — NHS vs Private
Mounjaro (tirzepatide) is available through two main routes in the UK: NHS specialist weight management services and private online prescribing. NHS access: Your GP can refer you to a tier 3 specialist weight management service, where clinicians assess your eligibility and prescribe Mounjaro if appropriate. This route is free at the point of care, but waiting lists vary significantly by region and can extend several months. Private access: You can obtain a UK prescription through online consultations with licensed prescribers following a clinical assessment. This avoids NHS waiting lists but involves private costs. Both routes require a confirmed BMI of 30 or above (or 27+ with weight-related health conditions) and assessment of your medical history. The NICE guidance on tirzepatide supports both NHS and private access pathways. Your choice depends on waiting times in your area, your preference for convenience, and whether you can afford private prescription costs.
Clinically BackedWeight Loss
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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.
Week 1 Mounjaro Costs & Starting Your Treatment
The 2.5mg starting dose in week 1 represents the first step of dose titration, escalating gradually over weeks based on tolerability. Private prescription costs: Expect to pay approximately £130–£180 for the first month's supply (4 weeks), which includes the pre-filled KwikPen and the first 2.5mg injection. Ongoing costs typically fall between £150–£250 monthly depending on your dose and provider—higher doses cost more. NHS prescribing: Free, but you must complete the NHS referral and assessment process first. In week 1, ensure your KwikPen is stored correctly (refrigerated at 2–8°C until first use), and familiarise yourself with the injection technique. Many providers offer video tutorials. Side effects in week 1 commonly include mild nausea, which usually improves as your body adjusts. Log your progress using our free progress tracker to monitor how you respond to the starting dose.
- 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 does Mounjaro cost in week 1 on a private prescription in the UK?
Private costs for the first month typically range from £130–£180 for the 2.5mg starting dose KwikPen. This is a one-time initial cost before escalation begins. Some providers offer subscription models or bulk discounts, so prices vary. NHS prescriptions are free but require referral to a specialist weight management service.
Can I get Mounjaro on the NHS in week 1?
Yes, through NHS tier 3 specialist weight management services. Your GP refers you, and the NHS service assesses your eligibility and prescribes Mounjaro free of charge if suitable. However, NHS waiting lists vary by region and can be several months long in some areas.
What happens during week 1 of taking Mounjaro?
Week 1 involves your first 2.5mg injection, which you self-administer once weekly (usually on the same day each week). You may experience mild nausea or appetite suppression. Side effects typically resolve within a few days. Your prescriber will advise you to continue for the full 4 weeks on this dose before escalation.
How does the dose titration work after week 1?
Mounjaro requires gradual escalation: weeks 1–4 are 2.5mg, weeks 5–8 are 5mg, weeks 9–12 are 7.5mg, and so on up to 15mg maximum. You stay on each dose for minimum 4 weeks before increasing. This reduces side effects and allows your body to adjust.
What's the difference between Mounjaro and Wegovy cost in the UK?
Mounjaro and Wegovy (semaglutide) have similar private prescription costs in the early weeks—roughly £130–£180 monthly. However, Wegovy starts at a lower dose (0.25mg) and costs may differ slightly depending on your provider and dose escalation schedule. Compare options with your 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.