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 It Best To Take Mounjaro?
Mounjaro is a once-weekly injection, so timing is simpler than daily medications — you choose one day each week that works for you and inject at roughly the same time. The injection itself takes just seconds using the Mounjaro KwikPen. What matters most is consistency: picking a day you'll remember and sticking to it. Your prescriber will guide you on the best injection day for your routine, and you can always adjust if needed. This guide explains the practicalities of Mounjaro timing in a UK context, including how the dose titration schedule works over the first several months.
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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 Dosing and Timing Work in Practice
Mounjaro is administered as a once-weekly subcutaneous injection, meaning you pick one day each week and inject at approximately the same time. There is no strict "best time of day" — morning, afternoon, or evening all work equally well. What matters is choosing a day you'll remember and maintaining that schedule weekly.
The dose titration schedule begins at 2.5 mg and escalates every four weeks if tolerated: 2.5 mg (weeks 1–4), 5 mg (weeks 5–8), 7.5 mg (weeks 9–12), 10 mg (weeks 13–16), 12.5 mg (weeks 17–20), and up to 15 mg (week 21 onwards). Each KwikPen contains four weekly doses, so you'll need a new pen each month. Your prescriber will determine whether you progress through doses based on how well you're tolerating the medication and your response. If you experience significant side effects like nausea or diarrhoea, your prescriber may delay escalation or keep you on a lower maintenance dose.
Consistency matters more than the specific time — your body adjusts to the regular weekly rhythm. Mark your calendar or set a phone reminder to help you remember injection day.
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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.
NHS Access and Private Prescription Routes in the UK
In the UK, Mounjaro (tirzepatide) is available through two routes: NHS specialist services and private prescription. NHS access is through tier 3 or 4 specialist weight management services, typically requiring a GP referral. NICE has approved tirzepatide for use within NHS specialist weight management services, but availability and waiting times vary significantly across regions and integrated care boards (ICBs). Many areas have substantial waiting lists.
Private access is available through GPhC-registered online pharmacies following an online consultation with a UK-licensed prescriber. This route does not require NHS referral and typically has shorter timescales. Whichever route you use, your prescriber will assess your eligibility based on BMI, weight-related health conditions, and individual health circumstances. Use our free BMI calculator and GLP-1 weight loss calculator to understand your starting point and projected outcomes at different doses.
- 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, you can inject Mounjaro in the morning, afternoon, or evening — there is no pharmacological advantage to any particular time of day. What matters is choosing a time that fits your routine and injecting at approximately the same time each week. This consistency helps you remember and maintain the weekly schedule.
What if I miss my weekly Mounjaro injection?
If you miss your injection, take it as soon as you remember within 4 days of your scheduled day. If more than 4 days have passed, skip that dose and take your next injection on your normally scheduled day. Never take a double dose. Maintain at least 72 hours between injections.
Can I change my injection day if it doesn't suit me?
Yes, you can adjust your injection day to a day that better suits your routine. However, ensure you maintain at least 3 days (72 hours) between injections. Discuss any change with your prescriber or pharmacist to ensure continuity of your prescription refills.
How do I inject Mounjaro using the KwikPen?
The Mounjaro KwikPen is a pre-filled auto-injection device. Your prescriber or pharmacist will demonstrate the technique. Generally: clean the injection site, remove the pen cap, hold the pen perpendicular to skin, press the button, and hold for 3 seconds. Common sites are the stomach, thigh, or upper arm. Rotate sites weekly to minimise irritation.
What should I do if I have side effects like nausea when I start Mounjaro?
Nausea is common when starting Mounjaro, particularly in the first few weeks. Eating smaller, less fatty meals often helps. Your prescriber may delay dose escalation if side effects are significant. Do not stop taking Mounjaro without medical guidance — discuss any concerns with your GP or prescriber, who can advise on management strategies or adjustment options.
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.