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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Mounjaro and General Anaesthetic — What You Need to Know
If you're taking Mounjaro (tirzepatide) and need surgery requiring a general anaesthetic, it's crucial to inform your anaesthetist and surgical team beforehand. Mounjaro can affect how your body responds to anaesthesia and may need to be paused before your procedure. This guide explains what you need to do, how to prepare, and what to expect when combining Mounjaro with general anaesthetic 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.
Why General Anaesthetic and Mounjaro Require Special Care
Mounjaro affects how your stomach empties food (gastric emptying) and can influence how your body processes medications, including anaesthetic agents. This means anaesthetists need to plan your anaesthetic carefully to ensure safety during surgery. Key concerns include:
- Delayed gastric emptying increasing aspiration risk (food entering airways during anaesthesia)
- Interactions between tirzepatide and anaesthetic medications
- Changes in blood sugar control during and after surgery
- Nausea and vomiting risk in recovery
Your anaesthetist will adjust your anaesthetic plan based on your Mounjaro use, including choosing appropriate medications and monitoring strategies. Always disclose your Mounjaro dose titration schedule and when you last injected, as this information is essential for safe anaesthesia planning.
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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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What to Do Before Surgery — Practical Steps
Tell your surgical team immediately that you're taking Mounjaro. Your GP and anaesthetist need this information at least 2 weeks before elective surgery. Most anaesthetists recommend pausing Mounjaro for a short period before your procedure — your anaesthetist will advise exact timings based on your surgery type and Mounjaro eligibility status.
Provide your medical team with your current Mounjaro dose, injection schedule, and how long you've been taking it. If you have a Mounjaro UK prescription from NHS specialist services or private online consultation, bring all documentation. Your anaesthetist will also want to know about any side effects you've experienced, particularly nausea or stomach issues, as these affect recovery planning.
- 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.
Should I stop taking Mounjaro before general anaesthetic?
Most anaesthetists recommend pausing Mounjaro before elective surgery, but timing depends on your procedure type and Mounjaro dose. Your surgical team will provide specific instructions — do not stop without their guidance. For emergency surgery, inform the anaesthetist immediately of your Mounjaro use so they can adjust your anaesthetic plan accordingly.
How far in advance should I tell my surgical team about Mounjaro?
Inform them as soon as you know surgery is needed, ideally at least 2 weeks before elective procedures. This gives your anaesthetist time to review your Mounjaro eligibility history, current dose, and adjust your anaesthetic plan safely. For emergency surgery, tell the anaesthetist and surgical team immediately upon arrival.
Can Mounjaro affect anaesthetic effectiveness?
Yes, Mounjaro can affect how your body processes anaesthetic medications. Your anaesthetist will adjust drug doses and choice of agents based on your Mounjaro use. This is why detailed disclosure is essential — your anaesthetist uses this information to ensure appropriate anaesthetic depth and safety throughout your procedure.
Will Mounjaro affect my recovery from anaesthesia?
Mounjaro may increase nausea and vomiting risk during recovery. Your anaesthetist will prescribe appropriate anti-nausea medications beforehand. Delayed gastric emptying from Mounjaro means you may need to fast longer after surgery. Follow all pre and post-operative fasting instructions your surgical team provides carefully.
What if I need emergency surgery while taking Mounjaro?
Tell the anaesthetist and surgical team immediately about your Mounjaro use. Provide your current dose and when you last injected. While emergency surgery cannot be delayed, your anaesthetist will use this information to manage anaesthetic risks appropriately and plan your recovery care, including anti-nausea medication and monitoring.
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