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 Should You Take Mounjaro in the UK?
Mounjaro (tirzepatide) is a prescription-only weight management injection available in the UK through NHS specialist services or private prescribing. The question of when you should take Mounjaro isn't about timing within the day—it's about whether you meet NHS and clinical eligibility criteria. Your GP or a licensed prescriber will assess your individual health situation to determine if this medication is appropriate for you. Understanding UK prescribing pathways, NICE guidance, and eligibility thresholds helps you navigate your options.
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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.
NHS Eligibility and When Mounjaro May Be Prescribed
In the UK, Mounjaro may be prescribed to adults who meet specific NHS criteria. You are typically eligible if you have a BMI of 30 kg/m² or above, or a BMI of 27–29.9 kg/m² alongside at least one weight-related health condition (type 2 diabetes, prediabetes, high blood pressure, abnormal blood fats, sleep apnoea, or cardiovascular disease). For people of South Asian, Chinese, Black African, or Black Caribbean heritage, lower BMI thresholds apply—eligibility may start at BMI 27.5 or above.
NICE has approved tirzepatide for use within NHS specialist weight management services (tier 3/4). However, NHS access varies significantly by region, and waiting lists can be lengthy. Private prescribing through a UK-licensed prescriber and GPhC-registered pharmacy offers faster access without NHS referral, following an online clinical assessment.
Use our free BMI calculator to check your personal BMI and understand where you fall within these thresholds. Your prescriber will also consider your full medical history, current medications, and whether you are pregnant, planning pregnancy, or breastfeeding—all factors that determine whether Mounjaro is suitable for you.
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 Timing: When to Start and How Dosing Works
Once prescribed, your Mounjaro KwikPen arrives with clear instructions on administration timing. The injection is given once weekly, ideally on the same day each week—you choose a day that suits you. You inject subcutaneously (under the skin) into the stomach, thigh, or upper arm, rotating injection sites each week.
Mounjaro dosing begins at 2.5 mg and increases every 4 weeks if tolerated: 5 mg (weeks 5–8), 7.5 mg, 10 mg, 12.5 mg, and up to 15 mg maximum. Your prescriber determines the escalation schedule based on your response and any side effects. If you miss a dose, take it within 4 days of the scheduled time; if more than 4 days have passed, skip that dose and resume your normal schedule. Our GLP-1 weight loss calculator can help you estimate potential weight loss outcomes at different doses based on clinical trial data.
NHS vs Private Routes: Timeline and AccessThe path you take affects when you can begin Mounjaro. NHS route: Speak to your GP about specialist weight management services in your area. Your GP may refer you to a tier 3 service, but waiting times vary from weeks to over a year depending on your region. Private route: You can access an online consultation with a UK-licensed prescriber within days, receive a prescription if approved, and have medication dispensed by a registered pharmacy—often within 1–2 weeks.
Both routes require a clinical assessment confirming eligibility and suitability. Neither offers Mounjaro without a prescription. Once started, regular follow-up appointments (NHS or private) monitor your progress, tolerance, and any side effects. Sustainable weight loss with Mounjaro typically requires concurrent dietary changes and increased physical activity—medication supports rather than replaces these lifestyle factors.
- 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 get Mounjaro on the NHS in the UK?
Yes, Mounjaro (tirzepatide) is approved by NICE for use within NHS specialist weight management services. However, access varies by region and ICB (Integrated Care Board), and waiting lists can be lengthy. Your GP can refer you to tier 3 services, but private prescribing may be faster if you meet eligibility criteria.
What is the ideal time of day to take Mounjaro?
Mounjaro is a once-weekly injection—you choose which day of the week to take it, ideally the same day each week for consistency. There is no specific ideal time of day; simply inject when convenient on your chosen day.
How does Mounjaro dose titration work?
Mounjaro starts at 2.5 mg weekly and increases every 4 weeks if tolerated: 5 mg, 7.5 mg, 10 mg, 12.5 mg, and up to 15 mg maximum. Your prescriber determines the escalation schedule based on your tolerance and response. Some people remain on lower doses if they achieve good results.
What if I miss a Mounjaro injection?
If you remember within 4 days of your missed dose, take it as soon as possible and resume your normal weekly schedule. If more than 4 days have passed, skip that dose and inject on your normal scheduled day. Never take a double dose.
Is Mounjaro different from Wegovy, and which is prescribed first in the UK?
Mounjaro (tirzepatide, dual GIP/GLP-1 agonist) and Wegovy (semaglutide, GLP-1 agonist only) are both licensed for weight management in the UK. Clinical trials show Mounjaro may produce slightly higher average weight loss (~21% vs ~15%), but both are prescribed based on individual eligibility and prescriber assessment. Neither is universally "first-line."
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.