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
Can You Take Antibiotics While Taking Mounjaro?
Yes, you can usually take most antibiotics while on Mounjaro, but there are important considerations to discuss with your GP or prescriber. Because Mounjaro (tirzepatide) can affect how quickly food moves through your stomach, it may impact how your body absorbs certain oral medications, including some antibiotics. This doesn't mean you can't take them together — it means your healthcare team needs to know about all medications you're taking so they can advise you properly. Always inform your GP or prescriber about any infection requiring antibiotics before starting 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.
How Mounjaro May Affect Antibiotic Absorption
Mounjaro slows gastric emptying — the rate at which food and medications move from your stomach into your small intestine. This effect typically reduces over time as your body adjusts to the medication. Because oral antibiotics are absorbed in the small intestine, slower gastric emptying may theoretically delay or affect absorption of some antibiotics.
- Intravenous antibiotics bypass the stomach entirely, so there is no interaction concern
- Most common oral antibiotics (amoxicillin, flucloxacillin, erythromycin) are not significantly affected by gastric emptying changes
- Certain antibiotics may need timing adjustments or monitoring — your GP will advise
- The effect on gastric emptying typically diminishes after the first few weeks of Mounjaro use
When your prescriber assesses whether Mounjaro is suitable for you, mention all regular medications and any recent infections requiring antibiotics.
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.
What You Should Do Before Taking Antibiotics
Always tell your GP or prescriber that you are taking Mounjaro before starting any antibiotic course. This applies whether you're accessing Mounjaro through NHS specialist tier 3 services or via private prescription. Your healthcare team can then:
- Choose the best antibiotic for your infection and your current Mounjaro dose
- Advise on timing — for example, taking antibiotics at a specific time of day relative to meals
- Monitor your treatment if needed
- Suggest alternative antibiotics if necessary
If you're unsure whether a medication interacts with Mounjaro, ask your pharmacist or GP — they have access to your full medication history and can give personalised advice. Use our free GLP-1 weight loss calculator to understand your Mounjaro dose context, and our BMI calculator to track your overall health progress alongside any medical treatment.
- 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.
Will antibiotics stop Mounjaro from working?
No. Antibiotics do not interfere with how Mounjaro works. However, Mounjaro may slow the absorption of some oral antibiotics. This is why it's important to inform your prescriber — they can choose the most suitable antibiotic or adjust timing if needed.
Should I stop Mounjaro if I need antibiotics?
No, you should not stop Mounjaro without guidance from your prescriber. Continue taking your regular Mounjaro injections as scheduled. Simply inform your GP or pharmacist that you're on Mounjaro when you're prescribed antibiotics.
Are intravenous antibiotics safer with Mounjaro than oral ones?
Intravenous (IV) antibiotics bypass the stomach completely, so gastric emptying does not affect their absorption. However, this doesn't mean oral antibiotics are unsafe — most are well-tolerated alongside Mounjaro. Your GP will recommend the most appropriate option for your infection.
Can I take my antibiotic at the same time as my Mounjaro injection?
Your Mounjaro injection is given once weekly subcutaneously (under the skin) — it doesn't interact with oral medications taken at the same time. However, discuss timing of oral antibiotics with your GP, who may suggest taking them at specific times relative to meals or other medications.
What if I'm not sure whether an antibiotic is safe with Mounjaro?
Always ask your GP, prescriber, or pharmacist before starting any new medication while taking Mounjaro. They have your full medical history and current prescriptions on file. If you're accessing Mounjaro privately, your prescriber will have documented your medication list during your clinical assessment.
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.