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
What Medications Cannot Be Taken With Mounjaro?
If you're taking Mounjaro (tirzepatide), it's important to know which other medications may interact with it. While most interactions are manageable, some medications require careful monitoring or dose adjustments. This guide covers the key drug interactions you should discuss with your prescriber or GP, how Mounjaro affects oral medications, and what safety steps to take before starting treatment. Always inform your healthcare provider of all medicines, supplements, and over-the-counter products you're taking.
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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.
Key Mounjaro Drug Interactions and Considerations
Oral contraceptives (the Pill) are the most important interaction to be aware of. Mounjaro may reduce how quickly oral medications are absorbed in your stomach by slowing gastric emptying. If you're taking the Pill, your prescriber will recommend adding a barrier method of contraception (such as condoms) or switching to a non-oral method for 4 weeks after starting Mounjaro AND for 4 weeks after each dose increase. This ensures contraceptive protection remains reliable.
- Diabetes medications (sulphonylureas and insulin) — your prescriber may need to adjust doses to reduce hypoglycaemia risk
- Oral medications in general — take these at least 30 minutes before your Mounjaro injection, or as advised by your GP
- Thyroxine (levothyroxine) — may require separate timing from other medications
- Certain blood pressure and heart medications — monitor blood pressure regularly
Always tell your prescriber about every medication you take, including over-the-counter pain relief, supplements, and herbal products. Many interactions are manageable with proper monitoring.
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.
Accessing Mounjaro Safely in the UK
Whether you access Mounjaro through the NHS or privately, a clinical assessment must happen before you start treatment. Your prescriber will review your complete medical history and current medications to identify any potential interactions. If you're prescribed Mounjaro via a UK-licensed online prescriber, the consultation includes detailed medication questions—this is standard safety practice, not optional.
Before starting Mounjaro: Bring a complete list of all medications to your GP appointment or online consultation. Include prescription medicines, over-the-counter drugs, vitamins, and supplements. This allows your prescriber to make informed recommendations and flag any concerns. Most people can safely take Mounjaro alongside their existing medications with minor adjustments. If you have questions about a specific drug interaction, contact your prescriber—never stop or change medications without professional guidance.
- 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.
Can I take paracetamol or ibuprofen with Mounjaro?
Yes, paracetamol and ibuprofen are generally safe to take with Mounjaro. However, if you experience nausea as a side effect, avoid ibuprofen on an empty stomach. Always take over-the-counter pain relief with food where possible, and inform your prescriber if you use these regularly.
Does Mounjaro affect how the contraceptive pill works?
Yes—Mounjaro slows stomach emptying, which may reduce oral contraceptive absorption. Your prescriber will recommend adding barrier contraception (condoms) or switching to a non-oral method for 4 weeks after starting and after each dose increase to ensure protection.
Will Mounjaro interact with my diabetes medication?
If you take sulphonylureas or insulin for diabetes, your prescriber will likely adjust your doses once you start Mounjaro. This is because Mounjaro itself affects blood sugar levels. Your GP will monitor this closely and arrange regular check-ups to ensure safe dosing.
What should I do if I'm unsure about a medication interaction?
Always tell your GP or prescriber about every medication you take during your initial consultation. They will check for interactions and advise on timing or dosing changes. Never stop or change medications without professional guidance, even if you suspect an interaction.
Can I take supplements or herbal products with Mounjaro?
Most supplements are safe with Mounjaro, but inform your prescriber about all of them—including vitamins, minerals, and herbal remedies. Some herbal products can affect blood sugar or digestion, so professional review is important before combining them with weight loss medication.
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.