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
Which Medications Cannot Be Taken With Mounjaro?
Mounjaro (tirzepatide) is a prescription-only weight management injection used by UK adults, but it can interact with certain other medications. Before starting Mounjaro from a KwikPen, it's essential to tell your prescriber about all medications you're currently taking — including over-the-counter products, supplements, and herbal remedies. Some medications require dose adjustments or monitoring, whilst others may not be suitable to use alongside Mounjaro. Your prescriber will assess any potential interactions during your clinical assessment before issuing a prescription.
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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 Medication Interactions With Mounjaro
Oral contraceptives (the pill): Mounjaro slows gastric emptying — how quickly food (and medications) leave your stomach. This can reduce how well oral contraceptives are absorbed. If you take the contraceptive pill, you should use an additional barrier method (condom) or switch to a non-oral contraceptive for 4 weeks after starting Mounjaro AND for 4 weeks after each dose increase. This is one of the most important drug interactions to be aware of.
Diabetes medications: If you take sulphonylureas (like gliclazide or glipizide) or insulin, Mounjaro may increase the risk of low blood sugar (hypoglycaemia). Your prescriber may need to adjust these doses, and you should monitor your blood sugar levels more carefully. This requires specialist medical supervision.
Other oral medications: Because Mounjaro slows gastric emptying, the absorption of any oral medication taken at the same time may be affected. Always inform your prescriber of all regular medications before starting treatment so they can assess individual risk.
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 Do Before Starting Mounjaro
Before your clinical assessment for Mounjaro, compile a complete list of all medications and supplements you're currently taking — including prescription medicines, over-the-counter painkillers, vitamins, herbal supplements, and any treatments from private healthcare providers. Be honest about all products, as even seemingly minor medications can interact.
During your assessment, your prescriber will review this list, discuss any necessary adjustments, and confirm whether Mounjaro is suitable for you. If you start any new medications whilst on Mounjaro, inform your prescriber. If you're unsure whether a specific medication is compatible, always ask your GP or pharmacist before starting — they can check your dose titration plan and ensure safety. Never stop or adjust other medications without medical 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 standard ibuprofen doses can generally be taken with Mounjaro. However, as with any medication, inform your prescriber of regular pain relief use during your clinical assessment. If you need frequent pain relief, discuss this with your GP to rule out underlying conditions requiring treatment.
Will Mounjaro affect my blood pressure medication?
Mounjaro itself may help lower blood pressure through weight loss, which could mean your blood pressure medication needs adjusting. Your prescriber should monitor your blood pressure regularly. Never adjust blood pressure medication doses yourself — always consult your GP, as changes require medical supervision.
What about thyroid medication and Mounjaro?
Mounjaro is not known to directly interact with thyroid medication (levothyroxine). However, weight loss can sometimes affect thyroid hormone requirements, so your GP may want to recheck your thyroid levels a few months after starting Mounjaro. Continue taking thyroid medication as prescribed unless your GP advises otherwise.
Can I take antidepressants with Mounjaro?
Most antidepressants do not have significant direct interactions with Mounjaro. However, some antidepressants can affect appetite or blood sugar, so your prescriber should know about them. Always provide a full medication list during your clinical assessment to ensure safety.
What if I'm taking multiple medications — is Mounjaro still safe for me?
Many people taking Mounjaro also use other medications successfully. The key is thorough disclosure during your clinical assessment. Your prescriber will review all interactions, suggest necessary monitoring or dose adjustments, and confirm whether Mounjaro is appropriate for your specific situation. This is why a proper assessment is essential before prescription.
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.