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 Anesthesia: What You Need to Know
If you're taking Mounjaro (tirzepatide) and need surgery or a dental procedure requiring anesthesia, it's important to inform your healthcare team in advance. Mounjaro can affect how your stomach empties and may interact with anesthesia protocols. This guide explains what you need to do before any surgical procedure to ensure your safety.
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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.
What Happens When You Take Mounjaro Before Surgery
Mounjaro is a GIP and GLP-1 receptor agonist that slows gastric emptying — the rate at which food and liquid leave your stomach. This is an important consideration before anesthesia because a full stomach during surgery increases the risk of aspiration (stomach contents entering the airway) under general anesthesia. Your anaesthetist needs to know you're taking tirzepatide so they can plan your anesthesia safely.
- Tell your surgical team at your pre-operative assessment that you take Mounjaro
- Your GP or prescriber may advise you to pause Mounjaro before surgery — typically 2–4 weeks beforehand, depending on the procedure
- Your anaesthetist may recommend fasting for a longer period than usual
- Inform all healthcare staff, including dentists, if you have a dental procedure requiring sedation
The exact guidance depends on the type and urgency of your procedure, so always discuss with your surgical team.
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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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NHS Guidance and Pre-Operative Assessment
During your NHS pre-operative assessment (usually 2–4 weeks before elective surgery), you'll be asked about all medications you're taking. Mention Mounjaro explicitly and bring the medication name (tirzepatide) in writing if helpful. Your anaesthetist will assess your individual risk and may adjust fasting protocols or recommend stopping Mounjaro before your surgery date.
If you're in a specialist weight management service through the NHS, your tier 3 team can liaise directly with your surgical team. For emergency surgery, inform the hospital staff immediately that you take Mounjaro so they can manage your anesthesia accordingly.
- 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 surgery?
Your surgical team or anaesthetist will advise whether to pause Mounjaro before your procedure. For most elective surgeries, stopping 2–4 weeks beforehand is recommended. For emergency surgery, inform staff immediately and they'll manage anesthesia accordingly. Never stop without guidance from your healthcare provider.
Why does Mounjaro affect anesthesia?
Mounjaro slows gastric emptying, meaning food and liquid stay in your stomach longer. During general anesthesia, a full stomach increases aspiration risk. Your anaesthetist needs this information to plan safer anesthesia protocols and may recommend extended fasting before your procedure.
Should I tell my dentist I take Mounjaro?
Yes, always inform your dentist before any procedure, including routine cleanings or extractions. If sedation is needed, your dentist must know you take tirzepatide so they can adjust their anesthesia plan accordingly. This applies to both NHS and private dental practices.
What if I need emergency surgery?
Inform hospital staff immediately that you take Mounjaro. Tell the anaesthetist explicitly. Your surgical team will manage anesthesia safely even without advance planning, but knowing you take tirzepatide helps them assess aspiration risk and plan appropriate precautions.
Can I restart Mounjaro after surgery?
Your surgical team or GP will advise when it's safe to restart Mounjaro, usually after you've recovered from anesthesia and can eat normally again. This typically takes a few days to a week. Never restart without guidance from your healthcare provider or prescriber.
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