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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When Is Best To Take Mounjaro? UK Timing Guide
Mounjaro (tirzepatide) is given as a once-weekly injection, and the timing of your injection is flexible — you can take it on any day of the week that suits you best. The key is consistency: choose the same day each week and stick to it. This page explains UK prescribing guidance for Mounjaro timing, how the dose titration schedule works, and what NHS services expect from patients receiving this prescription-only weight management medication.
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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.
Mounjaro Injection Timing — UK Prescribing Guidance
Unlike daily medications, Mounjaro does not require a specific time of day — only a consistent day of the week. You can inject on Monday morning, Wednesday evening, or any time that fits your routine. The important factor is maintaining the same day each week to avoid missed doses and keep your tirzepatide levels stable.
How to choose your Mounjaro day:
- Pick a day you will remember — many people choose the same day they do their weekly shopping or a familiar routine day
- Set a phone reminder for that day at a time convenient for you
- If you miss your usual day, you can inject within 4 days without affecting your schedule; beyond 4 days, skip that dose and return to your normal weekly day
- Never inject more than once every 3 days (72 hours minimum between doses)
Your prescriber will discuss your preferred day during your initial clinical assessment. Dose titration happens on schedule — you'll increase your dose every 4 weeks (e.g., from 2.5 mg to 5 mg in week 5, then 7.5 mg in week 9) regardless of which day you choose, as long as you're consistent.
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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.
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NHS Access and Prescription Timing for Mounjaro
In the UK, Mounjaro is accessed through NHS specialist tier 3 weight management services or private prescribing. Timing your first injection depends on your route: NHS services may have waiting lists of several months in some regions, whilst private prescribers can issue prescriptions within days of a clinical assessment. Your first dose will be 2.5 mg, given in week 1 of treatment. NICE guidance supports tirzepatide use for adults with BMI ≥30, or BMI 27–29.9 with weight-related health conditions. Your GP can refer you to NHS specialist services if you're eligible, or you can pursue private prescribing through a UK-licensed prescriber. Use our GLP-1 weight loss calculator to understand potential outcomes, and the BMI calculator to confirm your starting eligibility.
- 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.
Can I take Mounjaro at any time of day?
Yes. Mounjaro has no specific time requirement — you can inject in the morning, afternoon, or evening. What matters is choosing the same day each week. Many people inject on their chosen day at a time that suits their routine, such as after breakfast or before bed.
What if I miss my usual Mounjaro day?
If you're within 4 days of your scheduled injection day, take it as soon as you remember and continue your normal weekly schedule. If more than 4 days have passed, skip that dose and take your next dose on your usual day. Never take two doses within 72 hours.
How does the Mounjaro dose schedule work in the UK?
Starting dose is 2.5 mg in week 1. You increase to 5 mg in week 5, then escalate every 4 weeks (7.5 mg, 10 mg, 12.5 mg, 15 mg maximum) if tolerated. Your prescriber will advise on timing based on your response.
Does Mounjaro need to be taken with or without food?
Mounjaro is an injection, not an oral medication, so food does not affect it. You can inject regardless of whether you've eaten. Some people find injecting before meals helpful; others prefer after meals. Choose what feels comfortable.
How do I access Mounjaro on the NHS in the UK?
Ask your GP for a referral to a tier 3 specialist weight management service if you have a BMI ≥30 or BMI 27–29.9 with weight-related conditions. NHS access varies by region and waiting times can be long. Private prescribing through a UK-licensed prescriber is available without NHS referral.
Ready to take control of your weight loss journey?
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