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
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What Is a Mounjaro Plan and How Does It Work?
A Mounjaro plan is a structured prescription treatment programme using tirzepatide, a dual GIP and GLP-1 receptor agonist injection licensed for weight management in the UK. The plan involves starting at a low dose and gradually increasing over several weeks, alongside dietary changes and physical activity. Each plan is personalised based on your health, BMI, and individual response. Understanding how a Mounjaro plan works — from initial eligibility through dose titration to ongoing support — helps you make an informed decision about whether this prescription-only medication 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.
How a Mounjaro Plan Works — Dose Escalation and Timeline
A typical Mounjaro plan starts with a 2.5 mg dose for the first four weeks, then increases gradually if tolerated. The standard escalation follows this schedule: 5 mg (weeks 5–8), 7.5 mg (weeks 9–12), 10 mg (weeks 13–16), 12.5 mg (weeks 17–20), and 15 mg (week 21 onwards) as the maximum maintenance dose.
Each dose is a once-weekly injection using a pre-filled KwikPen device. You inject into your stomach, thigh, or upper arm, rotating sites each week. The entire escalation process typically takes 5–6 months to reach a stable maintenance dose, though your prescriber may adjust this timeline based on how you respond and any side effects.
Clinical trial data (SURMOUNT-1) showed that participants on Mounjaro lost an average of 15% to 21% of their body weight — though individual results vary significantly. This weight loss was achieved alongside a reduced-calorie diet and increased physical activity. Use our free GLP-1 weight loss calculator to estimate potential weight loss at different doses.
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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.
UK Eligibility, Access, and Getting Started With Your Plan
To be eligible for a Mounjaro plan in the UK, you must have a BMI of 30 kg/m² or above, or BMI of 27–29.9 with a weight-related health condition such as type 2 diabetes, high blood pressure, or sleep apnoea. Adults of South Asian, Chinese, Black African, or Black Caribbean heritage may qualify at lower BMI thresholds (from BMI 27.5) due to higher health risks at lower weights.
A Mounjaro plan can be accessed through the NHS via specialist tier 3 weight management services (requires GP referral; availability and waiting times vary by region) or through private prescribing following an online clinical assessment with a UK-licensed prescriber. Your prescriber will assess your medical history, current medications, and suitability before initiating a plan. Check your BMI using our free BMI calculator above to understand your starting point.
- 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 happens during the first week of a Mounjaro plan?
You receive your first 2.5 mg KwikPen and inject once during week 1. This is the starter dose to allow your body to adjust. Most people experience mild side effects like nausea or stomach changes — these typically reduce as your body adapts. Your prescriber will give you injection guidance and safety information before you start.
Can I stop my Mounjaro plan at any time?
Yes. Mounjaro is not a lifelong commitment. However, stopping suddenly may result in rapid weight regain. Most people continue for at least 1–2 years to achieve and maintain weight loss. Discuss stopping plans with your prescriber — they may suggest a gradual wind-down rather than abrupt cessation.
How does a Mounjaro plan compare to a Wegovy plan?
Mounjaro (tirzepatide) is a dual GIP and GLP-1 agonist; Wegovy (semaglutide) is a GLP-1 agonist only. Mounjaro showed average weight loss of 15–21% in trials; Wegovy showed approximately 15%. Both are once-weekly injections. The choice depends on your individual response, prescriber recommendation, and availability. Results vary between individuals.
What if side effects are severe during my Mounjaro plan?
Nausea, diarrhoea, and constipation are common but usually improve within 2–4 weeks. If severe side effects persist, contact your prescriber — they may pause escalation, reduce the dose, or suggest alternatives. Serious symptoms (severe stomach pain, allergic reactions) require immediate medical attention.
What support do I need alongside my Mounjaro plan?
Mounjaro works best with a reduced-calorie diet (typically 500 kcal/day deficit) and regular physical activity. Many people benefit from behaviour change support, nutritional guidance, or group weight management programmes. Your prescriber or GP can signpost you to NHS support services or private programmes aligned with your plan.
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.