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
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Who Can't Take Mounjaro — Contraindications Guide
Mounjaro (tirzepatide) is a prescription-only weight management injection, but it's not suitable for everyone. Certain medical conditions, medications, and life circumstances mean some people cannot safely take Mounjaro. Your GP or prescriber will assess whether this medication is appropriate for you based on your individual health. Understanding who shouldn't take Mounjaro helps ensure safe, personalised weight management decisions.
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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.
Absolute Contraindications — Who Must Not Take Mounjaro
The following people cannot take Mounjaro under any circumstances:
- Under 18 years old — Mounjaro is only licensed for adults; safety and effectiveness in children have not been established
- Pregnant or planning pregnancy — Tirzepatide may harm fetal development; women should use effective contraception during treatment and for 4 weeks after stopping
- Breastfeeding — It is unknown whether tirzepatide passes into breast milk; breastfeeding is not recommended while taking Mounjaro
- Allergy to tirzepatide or any ingredients — Serious allergic reactions are possible; inform your prescriber immediately if you have experienced allergic reactions to GLP-1 or GIP medications
- History of medullary thyroid cancer (MTC) — Tirzepatide may increase thyroid cancer risk in susceptible individuals
- Multiple endocrine neoplasia syndrome type 2 (MEN2) — Contraindicated due to thyroid cancer risk
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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.
Medical Conditions That May Prevent Mounjaro Use
Several medical conditions require careful assessment or may make Mounjaro unsuitable. Severe gastroparesis (stomach paralysis) is a major concern because tirzepatide slows gastric emptying, which could worsen symptoms. Pancreatitis history requires caution — inform your prescriber if you've had acute or chronic pancreatitis, as GLP-1 medications carry a small increased risk. Gallbladder disease may worsen with gradual weight management. Diabetic retinopathy (diabetes-related eye damage) requires monitoring, as weight loss can sometimes affect existing eye conditions. If you have any chronic health conditions, your GP or prescriber will assess the benefit versus risk before prescribing. Use our free BMI calculator to track your current weight status whilst discussing options with your healthcare team.
- 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 Mounjaro if I'm pregnant or trying to conceive?
No. Mounjaro is contraindicated in pregnancy. Women of childbearing age should use effective contraception during treatment and for 4 weeks after the last dose. If you're planning to become pregnant, discuss alternative weight management options with your GP.
What if I'm taking other medications — can Mounjaro interact?
Yes, potential interactions exist. Mounjaro may reduce absorption of oral contraceptives; add barrier contraception or switch to non-oral methods for 4 weeks after starting and after each dose increase. Diabetes medications may need adjustment. Always inform your prescriber of all medications you're taking, including over-the-counter medicines.
Can I take Mounjaro if I have a history of thyroid cancer?
No. Mounjaro is contraindicated in people with a personal history of medullary thyroid cancer (MTC) or multiple endocrine neoplasia type 2 (MEN2). Your prescriber will ask about thyroid cancer history during clinical assessment. If you're unsure, mention any thyroid conditions when discussing weight management with your GP.
Is Mounjaro safe if I have gastroparesis or stomach problems?
Mounjaro is not recommended if you have severe gastroparesis. Because tirzepatide slows stomach emptying, it can worsen this condition. If you have any history of stomach or digestion problems, inform your prescriber before starting treatment.
What's the difference between Mounjaro and Wegovy if I can't take one?
Mounjaro (tirzepatide) is a dual GIP and GLP-1 agonist, whilst Wegovy (semaglutide) is a GLP-1 agonist only. They have slightly different contraindications and mechanisms. If you can't take Mounjaro, Wegovy might be suitable — or vice versa. Your prescriber will assess both options 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.