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
Who Cannot Take Mounjaro in the UK?
Not everyone can safely take Mounjaro (tirzepatide), even if they meet the BMI eligibility criteria. Certain medical conditions, medications, and life stages make Mounjaro unsuitable. Understanding these contraindications is essential before pursuing prescription weight loss treatment in the UK. Your GP or licensed prescriber will assess your individual health profile to determine whether Mounjaro or an alternative like Wegovy is appropriate for you. Use our free BMI calculator above to check your starting point, then discuss prescription options with a healthcare professional.
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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 Groups Who Cannot Take Mounjaro
Mounjaro is not suitable for:
- Pregnant women or those planning pregnancy — tirzepatide may harm fetal development; women should use reliable contraception during treatment and for 4 weeks after stopping
- Breastfeeding mothers — it is unknown whether tirzepatide passes into breast milk
- People under 18 years old — not studied or approved for use in children and adolescents
- Individuals with a history of medullary thyroid cancer (MTC) — GLP-1 and GIP agonists are contraindicated due to animal study findings
- Those with multiple endocrine neoplasia syndrome type 2 (MEN2) — family history of MTC is also a contraindication
- People with severe diabetic retinopathy complications — rapid blood sugar changes may worsen vision problems
- Individuals with a documented allergy to tirzepatide or any excipients — though allergies are uncommon
Additionally, those with severe gastroparesis (stomach paralysis) or significant digestion disorders should not take Mounjaro, as it slows gastric emptying.
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.
Mounjaro vs Wegovy: Who Cannot Take Each
Both Mounjaro and Wegovy share most contraindications — neither is suitable during pregnancy, breastfeeding, or under age 18. However, there are subtle differences. Wegovy (semaglutide) is a GLP-1 only agonist, while Mounjaro (tirzepatide) uses dual GIP+GLP-1 mechanism. Clinical trial data (SURMOUNT for Mounjaro, STEP for Wegovy) showed comparable safety profiles, but individual tolerance differs. If you cannot tolerate Mounjaro due to gastrointestinal side effects or other reasons, your prescriber may suggest switching to Wegovy — a weight loss injection uk alternative requiring separate clinical assessment. Try our GLP-1 weight loss calculator to explore both options, then discuss suitability with your GP or licensed prescriber.
- 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 have type 2 diabetes?
Yes, Mounjaro can be used alongside diabetes treatment, but your diabetes medications may need adjustment. Inform your prescriber about all current medications. Mounjaro is licensed for weight management in adults with BMI ≥30, regardless of diabetes status. A clinical assessment will determine suitability.
Is Mounjaro safe if I have gallbladder problems?
Caution is required. Mounjaro may increase gallbladder-related complications. Inform your prescriber if you have a history of gallstones, pancreatitis, or bile duct issues. They may recommend Wegovy instead or monitor you closely. Clinical assessment is essential before prescription.
What if I'm taking oral contraceptives with Mounjaro?
Mounjaro may reduce the absorption of oral contraceptives, reducing their effectiveness. Women taking the contraceptive pill should add a barrier method or switch to a non-oral contraceptive for 4 weeks after starting Mounjaro and 4 weeks after each dose increase. Discuss alternatives with your GP.
Can I take Mounjaro if I have heart problems?
People with a history of heart attack or stroke may still be eligible for Mounjaro under NHS NICE guidance, as weight loss can improve cardiovascular health. However, individual assessment is required. Your GP or specialist will evaluate the risk versus benefit. Do not assume it is unsuitable without professional review.
What if I cannot tolerate Mounjaro — can I switch to Wegovy?
Yes, switching is possible if you experience intolerable side effects. Both are GLP-1-based weight loss injection uk options, though Wegovy is GLP-1 only whilst Mounjaro is dual GIP+GLP-1. Approximate dose equivalences exist, but any switch must be managed by your prescriber. A new clinical assessment may be required.
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.