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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Restarting Mounjaro After 3 Weeks โ What You Need to Know
If you've stopped taking Mounjaro after 3 weeks, restarting requires careful consideration of your current dose and health status. Whether you're pausing due to side effects, personal reasons, or exploring alternatives like Wegovy, this guide explains what happens when you restart a GIP/GLP-1 injection, how titration works, and the key differences between Mounjaro and other weight management options available in the UK. Always consult your prescriber before restarting any prescription medication.
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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/mยฒ).
While BMI isn't a perfect measure โ it doesn't account for muscle mass, bone density, or fat distribution โ 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 โ 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.
Restarting Mounjaro vs Considering Wegovy โ Key Differences
If you've been on Mounjaro for only 3 weeks, you're likely still on the starting dose (2.5 mg). When restarting, your prescriber will reassess your suitability, as Mounjaro requires an ongoing clinical assessment. Restarting typically means resuming the same dose schedule, unless side effects or health changes warrant adjustment.
Wegovy (semaglutide) is an alternative GLP-1 injection also licensed in the UK for weight management, but it works differently: Mounjaro is a dual GIP and GLP-1 receptor agonist, while Wegovy is a GLP-1-only medication. In clinical trials, Mounjaro showed average weight loss of approximately 15โ21% of body weight, compared to Wegovy's approximately 15% in the STEP-1 trial. Both require a prescription and clinical assessment. Your prescriber will decide which is most appropriate based on your individual health profile, previous response, and tolerance.
Clinically BackedWeight Loss
No appointments. No waiting rooms. Just care โ 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 โ 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 โ completely free.
Restarting Your Mounjaro KwikPen โ Practical Guidance
When restarting Mounjaro after a 3-week pause, store your KwikPen correctly: unopened pens must stay refrigerated at 2โ8ยฐC, and once started, can be kept at room temperature (below 30ยฐC) for up to 30 days. If your original pen has been stored properly and is within its 30-day window, you may resume with it; otherwise, a new pen will be needed.
Restart your regular injection schedule on your usual day of the week, unless your prescriber advises otherwise. If you've experienced significant side effects previously, discuss dose management with your GP or prescriber โ they may adjust your Mounjaro dose titration or suggest an alternative. Use our free BMI calculator to track your current baseline before restarting, and monitor progress with our GLP-1 weight loss calculator to set realistic expectations for your restart phase.
- 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 โ 5mg โ 7.5mg โ 10mg โ 12.5mg โ 15mg
- GLP-1 receptor agonist
- Up to 15โ17% body weight loss (STEP trials)
- Weekly injection, 5-step dose escalation
- NHS & private prescription available
- Doses: 0.25mg โ 0.5mg โ 1mg โ 1.7mg โ 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 | 15โ22.5% | 12โ17% |
| Key trial | SURMOUNT-1 (2022) | STEP 1 (2021) |
| Max dose | 15 mg weekly | 2.4 mg weekly |
| Escalation period | 20โ32 weeks | 16โ20 weeks |
| Administration | Weekly injection (pen) | Weekly injection (pen) |
| NHS availability | Private prescription only | NHS & private |
| Approx. private cost | ยฃ150โยฃ250/month | ยฃ150โยฃ300/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 โ 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 restart Mounjaro at the same dose after stopping for 3 weeks?
Possibly, but you must consult your prescriber first. If you were on 2.5 mg (the starting dose) and tolerated it well, restarting at the same dose is likely. If you experienced side effects, your prescriber may adjust the titration schedule or suggest alternatives like Wegovy.
What's the difference between Mounjaro and Wegovy for weight management?
Mounjaro (tirzepatide) is a dual GIP and GLP-1 agonist; Wegovy (semaglutide) is a GLP-1-only medication. Both are once-weekly injections licensed in the UK. Clinical trials show similar average weight loss (15โ21%), but mechanisms differ. Your prescriber will recommend the most suitable option based on your health history.
How should I store my Mounjaro KwikPen when restarting?
Unopened KwikPens must be refrigerated at 2โ8ยฐC. Once opened, your pen can be kept at room temperature (below 30ยฐC) for up to 30 days, then discarded. Never freeze. If your pen has been stored correctly and is within 30 days of first use, you can resume with it.
Do I need a new prescription to restart Mounjaro after 3 weeks?
Yes. You'll need to contact your prescriber or GP to restart any prescription medication. They'll reassess your eligibility, discuss why you stopped, and confirm whether restarting Mounjaro or switching to Wegovy is appropriate. This requires a fresh clinical assessment.
What if I had side effects on Mounjaro โ should I try Wegovy instead?
Side effects like nausea and constipation are common on GLP-1 medications and often improve with time. However, if side effects were severe, discuss alternatives with your prescriber. Wegovy may suit some people better, but it also carries similar side effects. Your prescriber will help determine the best option based on your specific experience.
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.