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 Start To Work?
Most people notice early signs of Mounjaro working within the first 2 to 4 weeks, though meaningful weight loss typically becomes visible after 8 to 12 weeks of consistent use. The dual GIP and GLP-1 mechanism of tirzepatide begins affecting appetite and fullness signals almost immediately, but your body needs time to adjust to each dose increase. Weight loss speed depends on your starting dose, lifestyle changes, and individual metabolism. Understanding how Mounjaro works and how to access it in the UK — whether through NHS specialist services or private prescription — helps you set realistic expectations for your weight loss journey.
10,000+ calculations today · NHS-aligned thresholds · 100% free
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.
Cost and Private Access for Mounjaro in the UK
Private prescription costs for Mounjaro in the UK typically range from £129 to £320 per month, depending on your dose and the provider. A standard Mounjaro KwikPen (4 weeks supply at one dose) costs between £100 and £250 through private online prescribing services. Dose escalation — moving from 2.5mg to 5mg to 10mg and beyond — happens gradually over weeks, so your monthly costs remain predictable during the titration period. The starting 2.5mg dose is usually the most affordable, with prices increasing as you reach therapeutic maintenance doses like 10mg or 15mg.
- Private access requires an online clinical assessment with a UK-licensed prescriber
- No NHS referral needed — available without GP involvement
- Payment is typically per pen or per month upfront
- Prescriptions dispensed by GPhC-registered pharmacies
- Most providers offer repeat prescriptions for ongoing supply
Your GLP-1 weight loss calculator can help you estimate which dose might be appropriate for your situation, though final dosing is always decided by your prescriber following assessment.
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: How to Access Mounjaro in the UK
NHS access is through specialist tier 3 or tier 4 weight management services, typically requiring a GP referral. NHS availability and waiting times vary significantly by region and ICB (Integrated Care Board). Many areas have waiting lists of months or even years. Once referred, you'll be assessed by a multidisciplinary team who will determine eligibility based on your BMI, health conditions, and circumstances.
Private route is faster: complete an online consultation, receive a prescription decision within 24 hours, and start treatment within days. You'll need to demonstrate you meet eligibility criteria (BMI 30+, or 27+ with weight-related health conditions), and your prescriber will ask about medical history, current medications, and contraindications. Both routes require genuine clinical assessment — Mounjaro is prescription-only and never sold without a prescription from a UK-licensed doctor or prescriber.
- 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.
Does Mounjaro work immediately?
Mounjaro begins affecting appetite within days of your first injection, but noticeable weight loss typically takes 4 to 8 weeks. Early signs include reduced hunger and feeling fuller after smaller meals. Meaningful results (visible on scales) usually appear by week 12 as your dose increases and your body adjusts to the medication.
How long until I see weight loss results on Mounjaro?
Most people see 2-4kg weight loss in the first month, with accelerating loss over 12 weeks as their dose increases toward therapeutic levels (10-15mg). Clinical trials showed average weight loss of 15-21% body weight over 72 weeks on full doses. Your progress tracker can help monitor your individual timeline.
What's the difference between NHS and private Mounjaro access?
NHS access is free but involves referral, assessment through specialist services, and potentially long waiting lists (months to years in many areas). Private access costs £129-£320 monthly, requires online consultation only, and treatment typically starts within days. Both require genuine clinical assessment and prescription.
How much does Mounjaro cost privately in the UK?
Private Mounjaro costs range from £100-£250 per KwikPen (4 weeks), depending on dose. Starting dose (2.5mg) is usually cheaper; higher maintenance doses (10mg, 15mg) cost more. Some providers offer bundled packages or repeat prescription discounts. Always confirm pricing before starting treatment.
Can I get Mounjaro without a prescription in the UK?
No. Mounjaro is prescription-only medication in the UK. You must complete a clinical assessment with a UK-licensed prescriber (via NHS or private online consultation) before you can legally receive a prescription. Never buy Mounjaro from unlicensed sources — it's unsafe and illegal.
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.