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 — Important Safety Information
If you take Mounjaro (tirzepatide) and need surgery, it's important to inform your GP, surgeon, and anesthetist before your procedure. Mounjaro affects how quickly food leaves your stomach, which can influence anesthesia safety and recovery. This guide explains what you need to know and when to pause your medication before surgery.
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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 You Must Tell Your Healthcare Team
Always inform your surgical team that you take Mounjaro before any scheduled procedure, including minor surgery, dental work, or investigations requiring anesthesia. Your GP, surgeon, and anesthetist need this information to plan your care safely.
Key points to communicate:
- The exact dose of Mounjaro you're taking
- When you last had an injection
- Any stomach or digestion issues you've experienced
- Any previous surgery complications
- All other medications you take
Your anesthetist may need to adjust their approach based on your Mounjaro use, as the medication slows gastric emptying (how quickly your stomach empties). This is a routine consideration and your healthcare team has experience managing patients on GLP-1 medications like tirzepatide.
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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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When to Stop Taking Mounjaro Before Surgery
Current guidance suggests pausing Mounjaro for at least one week before surgery, though your specific surgeon may advise differently based on the type of procedure. This timing helps reduce the risk of complications related to slow gastric emptying during and after anesthesia.
Your surgical team will give you specific instructions about when to stop and when to restart your injections. Never stop or restart Mounjaro without explicit guidance from your healthcare provider. If your surgery is urgent or emergency, inform the anesthetist immediately about your Mounjaro use so they can adjust their plan accordingly. After surgery, follow your surgeon's advice before resuming your normal injection schedule.
- 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.
Do I need to tell my dentist I take Mounjaro?
Yes. Even for minor dental procedures, inform your dentist and any anesthetist involved. Mounjaro can affect stomach emptying and anesthesia safety. Most dental procedures don't require stopping Mounjaro, but your dentist will advise based on the procedure type.
How long before surgery should I stop Mounjaro?
Generally, pause Mounjaro for at least one week before surgery, though your surgeon may give different guidance. If surgery is urgent or emergency, tell the anesthetist immediately so they can adjust their approach. Always follow your surgical team's specific instructions.
Can I take Mounjaro the day before surgery?
Your surgical team will advise. Most commonly, Mounjaro is paused for one week before surgery to allow stomach emptying to normalise. Your pre-surgery instructions will specify exactly when to have your last injection.
What if I have an emergency operation?
Inform the anesthetist and surgical team immediately that you take Mounjaro. They can adjust anesthesia techniques and monitoring accordingly. Emergency teams are experienced in managing patients on weight loss medications and will keep you safe.
When can I restart Mounjaro after surgery?
Follow your surgeon's specific guidance. Restart timing depends on the type of surgery and your recovery. Your surgical team will advise, typically allowing several days for your stomach to fully recover before resuming injections.
Ready to take control of your weight loss journey?
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