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 Shouldn't Take Mounjaro — Important Eligibility Criteria
Mounjaro (tirzepatide) is a prescription-only weight management injection available in the UK, but it's not suitable for everyone. Certain medical conditions, medications, and life circumstances mean some people cannot or should not take this GLP-1 receptor agonist. Understanding who shouldn't use Mounjaro helps ensure safe and appropriate prescribing within NHS tier 3 services and private prescribing pathways. Your GP or prescriber will assess your individual suitability during a clinical consultation.
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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.
Medical Conditions and Circumstances Where Mounjaro Is Contraindicated
Mounjaro should not be used in people with:
- Pregnancy or breastfeeding — tirzepatide may harm a developing baby and passes into breast milk; women of childbearing age should use contraception during treatment and for 4 weeks after stopping
- Personal or family history of medullary thyroid cancer (MTC) — GLP-1 agonists carry a theoretical risk in this population
- Multiple endocrine neoplasia syndrome type 2 (MEN 2) — contraindicated due to thyroid cancer risk
- Severe gastroparesis (stomach paralysis) — Mounjaro slows gastric emptying, which could worsen this condition
- Type 1 diabetes — Mounjaro is approved for type 2 diabetes and weight management only
- Acute pancreatitis — current or recent pancreatitis requires specialist assessment
- Severe kidney disease (eGFR below 15 mL/min/1.73m²) — limited safety data in severe renal impairment
- Allergy to tirzepatide or any excipients — documented hypersensitivity is an absolute contraindication
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.
Age, Medication Interactions, and NHS Assessment Considerations
Age and NHS context: Mounjaro is not licensed for anyone under 18 years old. For older adults, prescribers assess individual health carefully as muscle loss risk increases with age.
Medication interactions: If you take oral contraceptives, you must add a barrier method or switch contraception for 4 weeks after starting and 4 weeks after each dose increase — Mounjaro reduces oral medication absorption. People taking sulphonylureas or insulin for diabetes may need dose adjustments and require close monitoring.
NHS and private prescribing: Both NHS tier 3 specialists and private prescribers conduct thorough medical assessments. Be honest about all medical history, medications, and allergies. Your prescriber may recommend Mounjaro is unsuitable based on your individual health profile, even if you meet BMI eligibility criteria.
- 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 planning pregnancy?
No. Mounjaro is contraindicated in pregnancy and breastfeeding. If you're using oral contraception, you must add a barrier method or switch contraception during treatment and for 4 weeks after stopping. Discuss family planning with your GP before starting Mounjaro.
What if I have a family history of thyroid cancer — can I still take Mounjaro?
No. If you or a close family member have had medullary thyroid cancer (MTC) or multiple endocrine neoplasia type 2 (MEN 2), Mounjaro is contraindicated. GLP-1 agonists carry a theoretical risk in people with this history. Your GP will advise alternative options.
Does Mounjaro work for type 1 diabetes?
No. Mounjaro is licensed only for type 2 diabetes and weight management in adults. It is not approved for type 1 diabetes. If you have type 1 diabetes, discuss other weight management approaches with your diabetes team.
I have severe stomach problems — can Mounjaro help me lose weight?
It depends. Mounjaro slows how quickly food leaves your stomach, which could worsen severe gastroparesis. Your GP or prescriber must assess your condition carefully. You may not be suitable for Mounjaro, but other treatments might help.
What should I tell my prescriber before starting Mounjaro?
Tell your prescriber about all medical conditions, medications (especially diabetes drugs and oral contraceptives), kidney disease, pancreatitis history, thyroid conditions, allergies, and any family history of thyroid or endocrine cancers. Complete honesty ensures they assess your suitability accurately and safely.
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.