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 I Take Mounjaro in the UK?
Mounjaro (tirzepatide) is a once-weekly prescription injection, and timing is straightforward — you choose a day each week and inject at roughly the same time. In the UK, Mounjaro is prescribed through NHS specialist weight management services or private online prescribing following a clinical assessment. Your prescriber will explain the dosing schedule, starting with 2.5 mg and potentially increasing every four weeks up to a maximum of 15 mg. Understanding when and how to take Mounjaro correctly is essential for getting the best results alongside a reduced-calorie diet and increased physical activity.
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Calculate Your BMI Instantly
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 Prescribing and Mounjaro Timing
Mounjaro is administered once weekly — you inject the same day each week, ideally at a similar time to build a consistent routine. The MHRA-approved Mounjaro KwikPen comes pre-filled with four weekly doses per pack. In the UK NHS context, Mounjaro may be prescribed through tier 3 specialist weight management services if you meet eligibility criteria: a BMI of 30 or above, or 27–29.9 with weight-related health conditions such as type 2 diabetes, hypertension, or cardiovascular disease. Lower BMI thresholds (BMI 27.5+) apply if you are of South Asian, Chinese, Black African, or Black Caribbean heritage, due to higher health risks at lower BMI levels. Your prescriber will advise on the correct injection day and provide detailed guidance on using your KwikPen. Unlike some medications, there is no "best time of day" — consistency matters more than timing.
- Choose a fixed day each week (e.g. Tuesday morning) and stick to it
- You can inject at any time of day that suits your routine
- Rotation of injection sites (stomach, thigh, or upper arm) is important to prevent skin reactions
- Store unopened pens in the fridge (2–8°C); opened pens can be kept at room temperature for up to 30 days
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.
NHS Access and Dose Titration Schedule
In the UK, accessing Mounjaro on the NHS involves referral to your local tier 3 weight management service, though waiting times vary significantly by region and ICB. Dose titration — the gradual increase from 2.5 mg up to your maintenance dose — takes at least 16–20 weeks. Your prescriber will check how you're tolerating each dose before increasing. Common side effects like nausea often improve within the first few weeks at each dose level. Mounjaro vs Wegovy — both are once-weekly injections, but Mounjaro uses a dual GIP and GLP-1 mechanism, while Wegovy uses GLP-1 only. Clinical trials showed Mounjaro may help with slightly greater average weight loss, though individual results vary significantly. Use our free GLP-1 weight loss calculator to explore potential weight loss projections at different doses, and our BMI calculator to monitor your progress against NHS healthy weight targets.
- 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 day should I inject Mounjaro?
Choose any day of the week that suits you — consistency is key. Inject at roughly the same time each week (e.g. every Tuesday morning). You can change your chosen day if needed, but inform your prescriber. There is no "best" day medically; what matters is maintaining a weekly routine.
Can I take Mounjaro at different times of day?
Yes. Mounjaro can be injected at any time of day — morning, afternoon, or evening. Choose what fits your routine and stick to it. Unlike some medications, the specific time of day does not affect how Mounjaro works.
How do I get Mounjaro on the NHS in the UK?
Ask your GP for a referral to your local tier 3 specialist weight management service. You must meet NHS eligibility criteria: BMI 30+ or BMI 27–29.9 with weight-related health conditions. Waiting times vary by region. Private prescribing through a UK-licensed prescriber is an alternative route without NHS waiting.
What is the Mounjaro dosing schedule?
You start at 2.5 mg weekly for four weeks, then increase to 5 mg. Doses typically increase every four weeks (2.5 → 5 → 7.5 → 10 → 12.5 → 15 mg) based on tolerability. Your prescriber may keep you on a lower dose if side effects occur or if you achieve your goals.
Should I take Mounjaro before or after meals?
Timing relative to meals does not matter — Mounjaro works the same regardless. Inject whenever is convenient for you on your chosen day. Some people prefer injecting in the evening; others choose morning. The injection itself works through hormone activation, not food timing.
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.