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 a 3-Week Break
If you've stopped Mounjaro for three weeks, you'll need to restart carefully under your GP or prescriber's guidance. Mounjaro is a once-weekly GLP-1 and GIP receptor agonist injection used for weight management in UK adults. Stopping and restarting aren't straightforward — your prescriber needs to assess whether to resume at your previous dose or restart the titration schedule. This guide covers NHS-aligned guidance on restarting safely and what to expect.
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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 to Safely Restart Mounjaro After 3 Weeks
After a 3-week break, you should not restart Mounjaro without contacting your GP or prescriber first. The NHS tier 3 weight management services and MHRA guidance state that any treatment gap requires clinical reassessment. Your prescriber will consider several factors: why you stopped, your current health status, any side effects you experienced previously, and whether your weight or other health markers have changed.
- If you stopped due to side effects, your prescriber may recommend a lower starting dose or a slower dose titration schedule.
- If you stopped for another reason and tolerated your previous dose well, restarting at that dose may be appropriate — but this is a clinical decision, not automatic.
- A 3-week gap is short enough that complete retitration may not be necessary, but your prescriber has the final say.
Never attempt to restart without guidance. Contact your prescriber before using your next Mounjaro KwikPen. They'll advise based on your individual situation, which may differ from generalised guidance.
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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 Prescribing and What to Do Next
In the UK, Mounjaro for weight management is typically prescribed through NHS tier 3 specialist weight management services or via private online prescribing with a UK-licensed prescriber. If you were receiving Mounjaro on the NHS, contact your tier 3 service to discuss restarting. If you were using a private provider, reach out to them directly — they have your clinical history and can advise on dose resumption.
- Don't delay — gaps in treatment can affect your weight management progress and clinical outcome.
- Be honest about why you stopped (side effects, cost, other reasons) — this information helps your prescriber make the right decision.
- If you experienced specific side effects, mention them so your prescriber can plan a safer restart strategy.
- 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 restart Mounjaro at the same dose I was on before a 3-week break?
Possibly, but only your prescriber can decide. After a 3-week gap, your body's tolerance may have changed. If you tolerated your previous dose well and have no new health concerns, restarting at that dose might be appropriate. However, if you stopped due to side effects, your prescriber may recommend starting lower and titrating more slowly. Always get clinical guidance before restarting.
What happens if I restart Mounjaro too quickly after stopping?
Restarting without medical guidance could cause side effects to return suddenly, or trigger new ones if your tolerance has changed. Your body may also react differently after a break. This is why clinical reassessment is essential — your prescriber ensures a safe restart tailored to your current health status, not a generic resume.
Will stopping Mounjaro for 3 weeks affect my weight loss?
A 3-week break may slow your weight loss progress, but won't erase previous results. Your prescriber can help you re-establish momentum once you restart safely. If weight regain is a concern, discuss this openly with your GP or weight management service — they may adjust your dose plan or explore other support.
Should I contact my NHS tier 3 service or my GP to restart Mounjaro?
Contact whoever prescribed it. If you were referred to an NHS tier 3 weight management service, contact them directly — they manage your treatment plan. If a private prescriber issued it, contact that provider. Your GP can also help facilitate restart discussions, especially if coordinating with NHS services.
What if I can't afford to restart Mounjaro privately?
Discuss this with your GP. In some regions, NHS tier 3 services may offer Mounjaro as part of their weight management pathway — eligibility and waiting lists vary significantly. Your GP can advise on NHS options in your area and discuss alternatives if Mounjaro (tirzepatide) isn't currently accessible to you.
Ready to take control of your weight loss journey?
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