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
Mounjaro Weight Loss in Week 1: UK Cost and Access Guide
Starting Mounjaro in your first week involves understanding both the costs and how to access this prescription-only weight loss injection in the UK. Week 1 is your starting dose (2.5 mg) — the foundation of your treatment plan. This guide explains whether you can get Mounjaro through the NHS, private online prescription routes, what costs to expect, and how the initial access process works. Whether you're exploring NHS specialist services or private prescription options, knowing your pathway helps you make an informed decision about weight loss 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.
UK Private Prescription Costs and Access Routes
Private prescription costs for Mounjaro vary depending on the dose and provider. At the starting 2.5 mg dose in week 1, you can expect to pay approximately £129–£180 per month for private prescription access through a GPhC-registered online pharmacy. Higher doses (5 mg onwards) typically cost £150–£200+ per month. Each KwikPen contains 4 weekly injections, so costs reflect a month's supply.
How private prescription access works: You complete an online health questionnaire and video or phone consultation with a UK-licensed prescriber. If approved, they issue a prescription, which is then dispensed by a registered pharmacy. This route bypasses NHS waiting lists — many areas have waiting lists of months or years for NHS specialist weight management services. The weekly weight loss injection format (once per week) makes adherence straightforward.
- No NHS referral needed for private route
- Prescriber assesses your eligibility based on BMI and health factors
- Available within days, not months
- Costs are out-of-pocket — not covered by NHS prescription charges
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.
NHS vs Private: Which Route Is Right for You?
NHS access to Mounjaro requires referral to a tier 3 specialist weight management service through your GP. NICE has approved tirzepatide (Mounjaro) for NHS use, but availability varies dramatically by region and NHS Integrated Care Board (ICB). Some areas have waiting lists exceeding 18 months; others offer faster access. Week 1 of NHS treatment involves an initial assessment rather than immediate medication.
Private prescription route is faster: book an online consultation, receive a prescription within days, and begin your first 2.5 mg injection in week 1. This suits those who want to start immediately and can afford out-of-pocket costs. Use our GLP-1 weight loss calculator to estimate potential results with Mounjaro at different doses — this helps justify the investment in your weight management plan alongside NHS guidance.
- NHS: free but slower; private: faster but requires payment
- Both require clinical assessment for suitability
- Regional NHS availability varies significantly
- 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.
What is the average cost of Mounjaro in the UK for week 1?
At the 2.5 mg starting dose, private prescription Mounjaro typically costs £129–£180 per month for a KwikPen containing 4 weeks of injections. Each pen is one week's supply. Costs increase with higher dose escalations. NHS access is free but involves waiting lists and regional availability varies.
Can I get Mounjaro on the NHS for my first week?
NHS access to Mounjaro requires referral to a specialist tier 3 weight management service through your GP. NICE has approved it, but availability depends on your region and local ICB. Waiting lists can be very long. Private prescription offers faster access if you can afford costs.
How does the online prescription process work in week 1?
Complete a health questionnaire and consultation (video or phone) with a UK-licensed prescriber. They assess your BMI, health conditions, and medications for suitability. If approved, a prescription is issued and dispensed by a GPhC-registered pharmacy, usually within 2–5 days.
Will I lose weight in week 1 of Mounjaro?
Week 1 is your starting dose (2.5 mg) — significant weight loss typically doesn't occur in the first week. It takes several weeks of consistent injections and dose escalation to see meaningful results. Clinical trials showed weight loss develops over weeks and months alongside diet and activity changes.
Is Mounjaro cheaper than Wegovy in the UK?
Costs are comparable — both typically range £129–£250+ per month depending on dose. Mounjaro's dual GIP/GLP-1 mechanism differs from Wegovy's single GLP-1 action, but pricing is similar. Compare specific provider costs before deciding your weight loss injection option.
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.