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 vs Wegovy — Timing Guide for UK Users
Both Mounjaro (tirzepatide) and Wegovy (semaglutide) are once-weekly injections for weight management in the UK, but there are important differences in how and when you take them. While neither medication needs to be taken at a specific time of day, understanding the practical differences between these two medications — including their dose titration schedules, injection frequency, and how they fit into your weekly routine — can help you plan your treatment effectively. This guide compares the timing and administration of both medications to help you understand how they work in practice.
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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 vs Wegovy: Timing and Dose Schedule Differences
Mounjaro (tirzepatide) uses a four-week dose escalation schedule starting at 2.5 mg, with increases every 4 weeks if needed, reaching a maximum of 15 mg once weekly. You can inject any day of the week that suits your routine — there's no requirement for a specific time of day. Each Mounjaro KwikPen contains four weeks of doses (four pre-filled pens), so planning your injection day is straightforward.
Wegovy (semaglutide) has a longer 16-week dose titration schedule, starting at 0.25 mg and escalating to 2.4 mg maximum. Like Mounjaro, you can choose any day of the week for your injection — consistency matters more than timing to a specific hour. Both medications allow flexibility in choosing your injection day, whether you prefer a Monday, Wednesday, or weekend dose.
The key difference is escalation speed: Mounjaro reaches maintenance doses faster (4–8 weeks for 10 mg), whilst Wegovy's gradual titration spans 16+ weeks before reaching 2.4 mg.
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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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Choosing Your Injection Day and Building a Routine
The "best" time to take either Mounjaro or Wegovy is whichever day you'll remember consistently. Many UK users choose the same day each week — some prefer Monday mornings, others choose Friday evenings, and some prefer weekends when they have more time. What matters is maintaining at least 72 hours (3 days) between doses if you need to adjust your schedule.
Both medications should be stored in a refrigerator before use (2–8°C), but once you've injected, you don't need to time doses around meals or specific activities. You can inject into your stomach, thigh, or upper arm (thigh and stomach are easiest for self-injection). Try our GLP-1 weight loss calculator to understand your expected dose timeline, and use our progress tracker to log your injection dates and weight changes week by week.
- 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 and Wegovy at any time of day?
Yes. Neither Mounjaro nor Wegovy requires a specific time of day — you can inject in the morning, afternoon, or evening. What matters is choosing a consistent day each week. Many UK users pick the same day (e.g., every Monday) to build a routine and avoid missed doses.
What's the difference between Mounjaro and Wegovy injection schedules?
Mounjaro escalates doses every 4 weeks (from 2.5 mg to 15 mg maximum), whilst Wegovy escalates every 4 weeks too but takes 16+ weeks to reach the maximum 2.4 mg dose. Both are once-weekly injections, but Mounjaro's dual GIP+GLP-1 mechanism works differently to Wegovy's single GLP-1 action, which may affect how quickly you feel effects.
What if I miss my weekly Mounjaro or Wegovy injection?
If you miss a dose by 4 days or less, take it as soon as you remember and continue your normal schedule the following week. If more than 4 days have passed, skip that dose and resume your normal weekly schedule. Never take a double dose. Always maintain at least 72 hours between injections.
Should I inject Mounjaro or Wegovy before or after meals?
You don't need to time your injection around meals. Both medications can be injected at any time, regardless of whether you've eaten. However, both medications slow gastric emptying and reduce appetite, so you may naturally eat less at meals following your injection.
Which medication has a quicker onset — Mounjaro or Wegovy?
Clinical trials (SURMOUNT for Mounjaro, STEP for Wegovy) showed weight loss effects begin within weeks of starting, but individual timelines vary. Mounjaro's dual mechanism may show faster results for some users, whilst Wegovy's gradual titration means a longer ramp-up. Your GP or prescriber will recommend which suits your circumstances after a clinical assessment.
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.