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
When Does Mounjaro Start Working — UK Timeline & Access
Mounjaro (tirzepatide) typically begins affecting appetite within the first few days to a week of your first injection, though most people notice more significant weight loss effects between weeks 2 and 4. However, the timeline varies considerably between individuals. This guide explains when you can expect to feel changes, how to access Mounjaro in the UK, what it costs through private routes, and how NHS access works if you qualify for specialist weight management services.
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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.
How Mounjaro Becomes Effective — Timeline & What to Expect
Week 1: Most people report reduced appetite and changed food preferences within days of the first 2.5 mg dose, though this varies. Some experience nausea initially, which typically settles after a few days.
Weeks 2–4: As you remain on the starting dose, appetite suppression deepens. Many people begin noticing they eat less without feeling deprived. Your body is adapting to the medication.
Weeks 5–8: Your dose escalates to 5 mg. This is when weight loss often becomes more noticeable for many users, typically 1–2 kg per week depending on diet and activity. The medication's dual GIP and GLP-1 mechanism is now working at a stronger level.
Weeks 9–16+: Further dose escalations (7.5 mg, 10 mg) are introduced if tolerated. Average weight loss accelerates. Clinical trials showed participants on higher doses (15 mg) lost approximately 20% of their body weight over 72 weeks alongside reduced-calorie diet and increased physical activity.
Important: Results vary significantly between individuals. Some see rapid changes; others see gradual, steady progress. Try our free GLP-1 weight loss calculator to estimate potential results at different doses based on your starting weight.
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.
Mounjaro Cost in the UK — Private vs NHS Access Routes
Private prescription cost: Through private online prescribers, Mounjaro costs approximately £129–£180 per month for standard doses (5–10 mg), rising to £180–£220+ monthly for the maximum 15 mg dose. Prices vary between providers and may include consultation fees. This route does not require NHS referral and is often faster than NHS waiting lists.
NHS access: Mounjaro is available through NHS specialist tier 3 weight management services following NICE approval. However, access is limited by regional availability and significant waiting lists exist in many areas. Your GP can refer you if you meet eligibility criteria (BMI ≥30 or ≥27 with weight-related health conditions). NHS provision is free at point of use but availability is variable across ICBs.
Online clinical assessment: Private prescriptions require a consultation with a UK-licensed prescriber, typically completed online. You'll answer health questions, declare medications, and confirm you have no contraindications. A prescriber then decides if Mounjaro is appropriate for you.
- 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 quickly will I lose weight on Mounjaro?
Weight loss typically becomes noticeable between weeks 2–4 as your dose settles. Average losses are 1–2 kg per week during active dose escalation phases, though individual results vary significantly. Clinical trials showed average weight loss of 15–21% of body weight over 72 weeks alongside diet and exercise. Your personal rate depends on your starting weight, adherence to calorie deficit, activity level, and individual metabolism.
Does Mounjaro work from the first injection?
You may feel appetite reduction within days of your first 2.5 mg injection, but meaningful weight loss typically takes 2–4 weeks to become noticeable. The medication requires time to reach therapeutic levels in your system. Many people experience nausea initially (a known side effect) before appetite suppression becomes the dominant effect. Patience through the first month is important.
Is Mounjaro available on the NHS in the UK?
Yes, Mounjaro (tirzepatide) is approved by NICE for NHS use through specialist tier 3 weight management services. However, access is limited and waiting lists can be lengthy in many regions. Your GP can refer you if you meet eligibility criteria (BMI ≥30, or ≥27 with weight-related conditions). Availability varies significantly across NHS integrated care boards. Private prescription is often faster but involves out-of-pocket costs.
What is the cost of Mounjaro privately in the UK?
Private prescriptions for Mounjaro typically cost £129–£220 per month depending on dose strength (5 mg–15 mg), plus any online consultation fee. Prices vary between GPhC-registered providers. Some packages include follow-up consultations. This compares to NHS provision at no cost to eligible patients, but NHS access often involves waiting times of several months. Use our BMI calculator to check if you might meet NHS eligibility criteria.
How do I get a private Mounjaro prescription in the UK?
Complete an online consultation with a UK-licensed prescriber through a GPhC-registered online pharmacy. You'll answer health questions about your weight, medical history, and current medications. The prescriber assesses whether Mounjaro is suitable and, if approved, issues a prescription. Your dose begins at 2.5 mg, escalating weekly under clinical guidance. All prescriptions are issued by UK-licensed doctors only.
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.