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
What to Expect from Mounjaro in the First 4 Weeks
During the first 4 weeks of Mounjaro treatment, you'll be on the starting dose of 2.5 mg — a lower dose designed to help your body adjust to the medication. This is the dose titration phase, not yet the therapeutic dose, so significant weight loss is not the primary goal at this stage. Understanding what to expect in these early weeks, along with UK access routes and costs, can help you make an informed decision about whether this prescription-only tirzepatide injection is right for you.
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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 Mounjaro Costs and Access Routes
In the UK, there are two main ways to access Mounjaro: through the NHS specialist tier 3 weight management services, or through private online prescription services. NHS access typically requires a GP referral to your local specialist weight management service, though availability varies significantly by region and waiting lists can be lengthy — sometimes months or even years depending on your ICB area. Private access is available through GPhC-registered online pharmacies following an online clinical assessment with a UK-licensed prescriber. Private costs typically range from £129 to £320+ per month depending on your dose, with the starting 2.5 mg dose usually at the lower end of this range. Once you progress through dose titration to higher doses (5 mg, 10 mg, 15 mg), costs may increase. Your private prescriber will assess your eligibility during the online consultation, checking your BMI, any weight-related health conditions, and medication interactions. Unlike Mounjaro vs Wegovy comparisons based on their different mechanisms, cost varies mainly by prescription route and dose level.
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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: Route Comparison and Eligibility
The NHS route is free at point of care once prescribed through a tier 3 service, but access is limited to specialist services and subject to regional availability and NICE guidance. The private route offers faster access without referral — you can have a prescription within 24–48 hours in many cases — but you pay the full cost of the medication. To be eligible for either route, you generally need a BMI of 30 or above, or 27+ with at least one weight-related health condition such as type 2 diabetes, prediabetes, high blood pressure, or sleep apnoea. Your online prescription assessment will review your medical history, current medications, and confirm you're not pregnant or breastfeeding. Once your prescription is approved, your Mounjaro KwikPen will be dispensed by the registered pharmacy, with full instructions and support provided.
- 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 weight loss should I expect in the first 4 weeks of Mounjaro?
At the starting 2.5 mg dose during weeks 1–4, weight loss is typically minimal — often 0–2 kg. This is the adjustment phase. Clinical trials showed meaningful weight loss develops at higher doses (5 mg, 10 mg, 15 mg) over weeks 5–72. Individual results vary significantly based on diet, activity, and metabolism.
How much does Mounjaro cost per month in the UK privately?
Private Mounjaro costs typically range from £129 to £320+ per month depending on your dose and pharmacy. The starting 2.5 mg dose is usually at the lower end. Costs increase as you move through dose titration to 5 mg, 10 mg, and 15 mg. Always confirm the exact cost with your prescriber before treatment begins.
Can I get Mounjaro on the NHS in the UK?
Yes, Mounjaro (tirzepatide) is approved by NICE for NHS specialist weight management services. Access requires a GP referral to your local tier 3 weight management service. Availability and waiting times vary significantly by region. Ask your GP about NHS eligibility and local services in your area.
What happens after the first 4 weeks on Mounjaro?
After 4 weeks on 2.5 mg, your dose will increase to 5 mg for weeks 5–8, then continue escalating every 4 weeks (7.5 mg, 10 mg, 12.5 mg, 15 mg) based on your response and tolerance. Weight loss typically increases at higher doses. Your prescriber will monitor your progress throughout.
Is Mounjaro the same as Wegovy for cost and access in the UK?
Both are prescription-only weight management injections available through NHS and private routes in the UK. Costs vary by dose and pharmacy. Mounjaro (tirzepatide) is a dual GIP and GLP-1 agonist, while Wegovy (semaglutide) is a GLP-1 agonist only — different mechanisms may lead to different results for different people. Your prescriber can advise which suits you.
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.