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 to Take Mounjaro — Timing and Scheduling
Mounjaro (tirzepatide) is a once-weekly injection, which means the timing is about choosing a consistent day each week that fits your routine. Unlike daily medications, there's no specific time of day you need to inject — your prescriber will help you select a day that works best for you. Whether it's Monday morning or Friday evening, what matters is maintaining that same day every week. This guide explains Mounjaro timing, injection schedules, and how the NHS supports tirzepatide treatment in the UK.
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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 Timing and Weekly Schedule
Mounjaro is injected once every seven days — the exact time of day is flexible and not medically significant. You can inject at any time that suits your routine, though consistency helps with remembering your weekly dose. Many people choose the same day and time weekly (for example, every Monday morning) to establish a routine, but this is a personal preference rather than a medical requirement.
Each Mounjaro KwikPen contains four pre-filled doses, providing a four-week supply. Your prescriber will initiate you at 2.5 mg and typically increase the dose every four weeks — so you'll progress through 2.5 mg, 5 mg, 7.5 mg, 10 mg, 12.5 mg, and potentially up to the maximum 15 mg dose. The minimum time between injections is 72 hours (3 days), though weekly dosing is standard.
- Minimum 72 hours between doses
- Standard schedule: same day every 7 days
- Time of day: flexible and not medically critical
- Each KwikPen covers 4 weeks of treatment
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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 Eligibility and Mounjaro Access in the UK
In the NHS, access to Mounjaro (tirzepatide) is through specialist tier 3 or tier 4 weight management services, not standard GP prescription. NICE has approved tirzepatide for use within NHS weight management pathways for adults with a BMI of 30 kg/m² or above, or 27–29.9 kg/m² with weight-related health conditions. Once prescribed through NHS specialist services, your injections are dispensed on a weekly schedule. Eligibility criteria include type 2 diabetes, prediabetes, hypertension, abnormal blood fats, or cardiovascular disease history.
- NHS access via specialist weight management tier 3 services
- BMI ≥30, or ≥27 with comorbidities
- Lower thresholds for South Asian, Black African, and Caribbean adults
- Regional variation in NHS availability and waiting times
Private prescribing offers faster access outside the NHS pathway. Following an online clinical assessment with a UK-licensed prescriber, if Mounjaro is clinically appropriate, your prescription is dispensed by a GPhC-registered pharmacy — typically with next-day or rapid delivery. Private patients also follow the same once-weekly injection schedule, though there may be flexibility in delivery timing. The choice between NHS and private routes depends on your circumstances, regional NHS availability, and cost considerations. Always inform your prescriber of any other medications, as Mounjaro may affect absorption of oral contraceptives and certain diabetes medications.
- Private prescribing available without NHS referral
- Prescription issued following online clinical assessment
- Dispensed by UK-registered pharmacies
- Same once-weekly injection schedule applies
- Inform prescriber of all current medications
- 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 time of day should I inject Mounjaro?
There is no specific time of day required for Mounjaro injection. You can inject in the morning, afternoon, or evening — what matters is consistency. Choose a time and day each week that fits your routine, and stick to that schedule. This helps establish a habit and reduces the chance of missed doses.
Can I change my Mounjaro injection day?
Yes, you can change your injection day if needed. The minimum time between injections is 72 hours (3 days). If you need to shift your weekly schedule, ensure at least 3 days have passed since your last injection, then resume your new day weekly. Contact your prescriber if you're frequently missing your scheduled day.
What happens if I miss a Mounjaro dose?
If you miss a dose, the guidance depends on timing. If fewer than 4 days have passed, inject as soon as you remember and resume your normal schedule. If more than 4 days have passed, skip that dose and take your next injection on the normally scheduled day. Never take two doses within 72 hours of each other.
Is Mounjaro available on the NHS in my area?
Mounjaro access on the NHS depends on your region. Specialist tier 3 weight management services in some ICBs have approved tirzepatide, but availability and waiting times vary significantly. Contact your GP for referral to your local specialist weight management service, or ask about the current status of Mounjaro prescribing in your area.
How does Mounjaro dose timing work with the titration schedule?
Mounjaro starts at 2.5 mg weekly and increases every 4 weeks (2.5 mg → 5 mg → 7.5 mg → 10 mg → 12.5 mg → 15 mg). You stay on each dose for a minimum of 4 weeks before escalation. Your prescriber assesses your tolerance and response before recommending a dose increase. The day and time of your weekly injection remains consistent throughout.
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.