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
Antibiotics and Mounjaro — What You Need to Know
If you're taking Mounjaro (tirzepatide) and have been prescribed antibiotics, you may be concerned about potential interactions. Mounjaro can slow gastric emptying—how quickly food and medications move through your stomach—which may affect how your body absorbs oral antibiotics. This guide explains the interaction between antibiotics and Mounjaro, what to tell your prescriber, and how to take both medications safely. Always inform your GP or prescriber of all medications before starting any new treatment.
10,000+ calculations today · NHS-aligned thresholds · 100% free
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 Affects Medication Absorption
Mounjaro slows gastric emptying, meaning food and medications spend longer in your stomach before moving into your intestines. This can reduce how quickly oral antibiotics are absorbed into your bloodstream, potentially affecting their effectiveness.
The extent of this effect varies between individuals and may decrease over time as your body adapts to the medication. Some antibiotics are more affected than others—particularly those that rely on rapid absorption for optimal efficacy, such as certain quinolones and macrolides.
- Gastric emptying effects are usually most pronounced at higher Mounjaro doses (10–15 mg)
- Effects tend to diminish after the first 8–12 weeks as your body adjusts
- Intravenous antibiotics bypass the stomach entirely and are not affected
Your prescriber will assess whether an alternative antibiotic or adjusted timing is needed based on your specific antibiotic class and Mounjaro dose.
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 to Tell Your GP or Prescriber
Before starting any antibiotic while on Mounjaro, inform your healthcare provider that you are taking tirzepatide and your current dose. Your prescriber may:
- Choose an intravenous antibiotic if available and clinically appropriate
- Recommend spacing your Mounjaro injection and antibiotic doses further apart
- Monitor you more closely for signs of infection
- Switch to an alternative antibiotic not affected by delayed gastric emptying
Do not adjust your Mounjaro dose or skip doses to take antibiotics without medical guidance. Your GP can advise on the safest approach for your individual situation. The same caution applies with other oral medications—always disclose your full medication list.
- 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 be less effective while taking Mounjaro?
Possibly. Mounjaro slows gastric emptying, which may reduce how quickly oral antibiotics are absorbed. However, most people still absorb enough of the antibiotic to be effective. Your prescriber can assess your specific antibiotic and adjust the approach if needed. Intravenous antibiotics are unaffected.
Should I stop taking Mounjaro if I'm prescribed antibiotics?
No. Do not stop Mounjaro without your prescriber's guidance. Instead, inform your GP or prescriber that you take tirzepatide. They can choose an appropriate antibiotic or adjust timing. Stopping Mounjaro abruptly could affect your weight management plan.
How long does Mounjaro affect medication absorption?
Mounjaro's effect on gastric emptying is usually most noticeable in the first 8–12 weeks. Effects often diminish as your body adapts, though some slowing may persist. Your prescriber considers this when recommending an antibiotic.
Can I take antibiotics at a different time of day to avoid interaction?
Possibly, but timing alone may not fully overcome the absorption delay caused by Mounjaro. Your prescriber is the best person to advise on optimal timing for your specific antibiotic. Some antibiotics require consistency with food or other medications.
Do I need to tell my GP I'm on Mounjaro before any treatment?
Yes, absolutely. Always inform any healthcare provider—GP, dentist, hospital, prescriber—that you take tirzepatide (Mounjaro) and your current dose. This applies to antibiotics, other medications, and any medical procedure or investigation.
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.