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 Can You Resume Mounjaro After Surgery?
If you're taking Mounjaro (tirzepatide) and facing planned surgery, you'll need to pause your injections temporarily. The timing for resuming depends on the type of surgery, your recovery, and your GP's assessment. Most UK guidelines suggest stopping Mounjaro 2–4 weeks before elective surgery and waiting until you've fully recovered before restarting — typically 2–4 weeks post-operation. Always discuss your individual situation with your surgical team and prescriber before stopping or restarting your tirzepatide treatment.
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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.
Why Mounjaro Must Be Paused Before Surgery
Mounjaro slows gastric emptying — the rate at which food leaves your stomach. This delayed gastric function increases the risk of complications during and after surgery, including aspiration (stomach contents entering the airway) and nausea. Anaesthetists recommend pausing GLP-1 and GIP/GLP-1 medications before procedures requiring general anaesthesia.
Stopping Mounjaro also reduces the risk of dehydration and electrolyte imbalance during surgery and recovery. Your surgical team will provide specific guidance based on your procedure type. For minor procedures under local anaesthetic, timing may differ — discuss this with your surgeon and GP. Document all your medications with the hospital pre-assessment team to ensure safe anaesthesia planning.
The NHS recommends stopping tirzepatide at least 2 weeks before elective surgery, though some anaesthetists suggest 3–4 weeks for major operations.
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.
When to Restart Mounjaro After Surgery
Restart timing depends on your recovery and what you can tolerate eating. Most patients can resume Mounjaro 2–4 weeks after surgery, once they are:
- Eating normally or near-normal meals without nausea
- Fully mobile and managing daily activities
- Clear of post-operative complications
- Approved by their GP or surgical team
Do not restart your Mounjaro KwikPen without GP or prescriber approval. If you resume too early and experience severe nausea or vomiting, stop immediately and contact your GP. Your prescriber may recommend restarting at your current dose or stepping down to a lower dose if your stomach is still recovering. Recovery times vary — listen to your body and follow your medical team's guidance.
- 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 the day before surgery?
No. Stop Mounjaro at least 2 weeks before elective surgery. Most UK guidelines recommend 3–4 weeks for major procedures. Discuss your specific surgery date with your anaesthetist and prescriber to confirm the exact stop date. Do not take your weekly injection if it falls close to your surgery date.
What if I miss doses while recovering from surgery?
Missing doses during recovery is normal and medically appropriate. Do not try to "catch up" with double doses. Once cleared to restart by your GP, resume at your next scheduled injection day and continue your normal weekly routine. Your prescriber may adjust your dose schedule during recovery.
Will restarting Mounjaro affect my surgical wound healing?
No direct evidence shows tirzepatide harms wound healing. However, delayed gastric emptying and potential nausea during early recovery could affect nutrition, which supports healing. Ensure adequate protein and nutrient intake before restarting. Your GP can advise on optimal timing for your individual recovery.
What if I had emergency surgery and couldn't stop Mounjaro beforehand?
Inform the surgical team immediately that you take tirzepatide. Anaesthetists can manage this and will monitor you closely for aspiration risk and nausea. Recovery may be slower. Contact your prescriber after surgery to discuss when it's safe to resume your regular injection schedule.
Can I use our GLP-1 weight loss calculator after surgery?
Yes, but only once you've resumed Mounjaro and reached a stable dose post-recovery. Our free GLP-1 calculator can help estimate weight loss projections once your treatment is back on track. Discuss realistic timelines with your GP — surgery recovery may temporarily pause weight loss progress.
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.