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 Work in the UK?
Mounjaro (tirzepatide), a GLP-1 receptor agonist and GIP receptor agonist, typically begins showing weight loss results within 4 to 8 weeks of starting treatment. However, the timeline varies significantly between individuals and depends on dose, diet, physical activity, and how your body responds to the medication. This guide explains when you might expect to see changes, how much Mounjaro costs in the UK, and how to access it through both NHS and private routes.
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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 Cost and Timeline for Mounjaro
Mounjaro is available privately in the UK through GPhC-registered online pharmacies following a clinical assessment. Private costs typically range from £129 to £320 per month, depending on your dose and the provider. The starting dose (2.5 mg) is usually the most affordable, with costs increasing as you progress through the titration schedule (5 mg, 7.5 mg, 10 mg, 12.5 mg, and 15 mg maximum). Most people remain on their maintenance dose for several weeks before increasing, meaning your initial monthly cost may be lower. You'll need to budget for ongoing prescriptions — there is no NHS subsidy for private Mounjaro. The KwikPen device contains 4 doses (4 weeks of treatment), so costs are typically quoted per month or per 4-week supply. Private prescribing also avoids NHS waiting lists, meaning you can often start within days of your online consultation.
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 Access: Timeline and Getting Started
NHS route: Access is through tier 3 specialist weight management services. Your GP must refer you, but NHS waiting lists can be months or even years in many regions. Once assessed and approved, NHS prescribing is free. Private route: Faster access — typically within 1–7 days of completing an online consultation. A UK-licensed prescriber reviews your health history and issues a prescription if appropriate. Your prescription is then dispensed by a GPhC-registered pharmacy. No NHS referral needed. Most people starting privately see initial appetite reduction within the first 2 weeks, with measurable weight loss typically visible by week 4–6. Use our free GLP-1 weight loss calculator to project potential results at different doses, and the BMI calculator to track your starting point and progress.
- 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 many weeks until I see weight loss with Mounjaro?
Most people report initial appetite reduction within 1–2 weeks. Measurable weight loss typically appears by week 4–8, though individual timelines vary. Slower initial results are common if you're on the starting 2.5 mg dose. Results depend on diet, activity, and individual metabolism.
Is Mounjaro free on the NHS in the UK?
Yes, Mounjaro is free on the NHS if prescribed through a specialist tier 3 weight management service. However, NHS access is limited and waiting lists are very long in most regions. Many people access it privately instead to avoid delays.
How much does Mounjaro cost privately in the UK?
Private Mounjaro costs typically range from £129 to £320 per month depending on your dose. Starting dose (2.5 mg) is usually cheapest. Costs increase as you titrate up. Each KwikPen contains 4 weeks of doses. Budget accordingly for ongoing prescriptions.
How quickly can I start Mounjaro privately?
You can usually start within days of your online consultation. After completing a clinical assessment with a UK-licensed prescriber, your prescription is issued and dispensed by a GPhC-registered pharmacy. NHS route takes much longer due to specialist service waiting lists.
Do I need a GP referral to get Mounjaro privately?
No. Private Mounjaro is accessed via an online consultation with a licensed prescriber — no GP referral needed. The prescriber assesses your eligibility based on your health history. Your GP doesn't need to be involved, though informing them is advisable for your medical records.
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.