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 I Take Antibiotics With Mounjaro?
Yes, most antibiotics can be taken with Mounjaro, but there are important considerations. Mounjaro may slow how quickly your stomach empties, which can affect how some oral medications—including certain antibiotics—are absorbed. The key is timing and informing your prescriber. Always tell your GP or the doctor assessing your Mounjaro prescription about any antibiotics you're taking or have been prescribed, so they can advise on safe use together.
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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 Affects Medication Absorption
Mounjaro (tirzepatide) is a GIP and GLP-1 receptor agonist that slows gastric emptying—the rate at which food and medication leave your stomach. This delayed gastric emptying can reduce how quickly your body absorbs some oral medications, including antibiotics. For most people, this effect is temporary and reduces over time as your body adapts to the medication.
Common antibiotics such as amoxicillin, penicillin, and trimethoprim are generally safe to use with Mounjaro, but absorption may be slightly delayed. This means the antibiotic may take longer to reach its full effectiveness in your bloodstream. In most cases, this doesn't prevent the antibiotic from working—it may just take an extra hour or two to reach peak levels.
- Inform your prescriber about any antibiotics before starting or adjusting your Mounjaro dose titration
- Take antibiotics as directed on the prescription label
- If you have concerns about effectiveness, contact your GP
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.
When to Seek Medical Advice
Contact your GP or prescriber immediately if you're prescribed an antibiotic and have questions about taking it with Mounjaro. Certain antibiotics may interact differently depending on your individual health, kidney function, or other medications you're taking. Your GP can advise whether any adjustment is needed—such as taking your antibiotic at a different time of day away from food, or spacing doses further apart.
If you're on a UK NHS prescription for Mounjaro through a specialist weight management service, or a private Mounjaro UK prescription, always mention any new medications to your healthcare team. This ensures your treatment plan remains safe and effective throughout your weight management journey.
- 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 Mounjaro stop my antibiotic from working?
No. Mounjaro may slow how quickly the antibiotic is absorbed, but it doesn't prevent it from working. Most antibiotics remain fully effective even if absorption is delayed by a few hours. Always complete the full course of antibiotics as prescribed.
Should I take my antibiotic at a different time if I'm on Mounjaro?
Most people don't need to change the timing. However, if your GP advises you to space doses differently, follow their guidance. Taking antibiotics with water on an empty stomach may help absorption, but check the antibiotic label first.
Are there antibiotics I should avoid with Mounjaro?
Most common antibiotics are safe with Mounjaro. However, some oral medications are more affected by delayed gastric emptying. Your prescriber or GP can review your specific antibiotic and advise if any precautions are needed.
Does Mounjaro interact with other oral medications?
Yes. Mounjaro may affect absorption of oral contraceptives (which is why additional contraception is recommended for 4 weeks after starting or dose changes) and potentially other oral medicines. Always inform your healthcare team of all medications you take.
What's the difference between Mounjaro and other weight loss injections like Wegovy?
Mounjaro is a dual GIP and GLP-1 agonist, while Wegovy (semaglutide) is a GLP-1 agonist only. Both may affect medication absorption similarly. Both require a UK prescription and clinical assessment before use.
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.