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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Mounjaro And Hyperthyroidism — What You Need To Know
If you have hyperthyroidism and are considering Mounjaro (tirzepatide) for weight management, it's important to understand how this prescription injection may interact with your thyroid condition. Mounjaro is a dual GIP and GLP-1 receptor agonist approved in the UK for adults with obesity or overweight with weight-related health conditions. However, thyroid conditions require careful assessment before starting any new medication. This guide explains what you need to know about Mounjaro, hyperthyroidism, and how to access safe prescribing through the UK healthcare system.
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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.
Mounjaro And Thyroid Health — Clinical Considerations
Mounjaro is not specifically contraindicated in hyperthyroidism, but it does require a thorough clinical assessment from a prescriber who understands your thyroid status. GLP-1 receptor agonists like Mounjaro can affect appetite, nausea, and gastric function — symptoms that may overlap with or mask thyroid-related symptoms, making monitoring more complex.
Key considerations for hyperthyroidism:
- Mounjaro may cause nausea and appetite changes, which can complicate thyroid symptom monitoring
- Thyroid medications (such as propranolol or antithyroid drugs) may need dose adjustment if weight loss is significant
- A prescriber must know your full thyroid history, current medication, and whether your hyperthyroidism is controlled
- Regular thyroid function tests (TFTs) may be needed during tirzepatide treatment
Any prescriber assessing you for Mounjaro will ask about your thyroid condition as part of standard medical history. If your hyperthyroidism is well-controlled and stable, Mounjaro may be safe — but this must be individually assessed.
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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.
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Accessing Mounjaro In The UK — Routes And What To Expect
In the UK, Mounjaro is available through two routes: NHS specialist services and private online prescribing. NHS access: Referral to a tier 3 specialist weight management service through your GP, where thyroid history is fully reviewed. Private access: Online consultation with a UK-licensed prescriber who will assess your full medical history, including hyperthyroidism, before issuing a prescription. Both routes require clinical assessment — you cannot buy Mounjaro without a valid prescription from a registered prescriber. Private prescriptions typically cost £129–£280 per month depending on dose, and are dispensed by GPhC-registered pharmacies. Use our GLP-1 weight loss calculator to understand projected outcomes with Mounjaro, and our BMI calculator to assess where you sit on NHS eligibility thresholds.
- 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 hyperthyroidism?
Mounjaro is not automatically contraindicated in hyperthyroidism, but requires individual assessment by a prescriber who knows your thyroid status, current medication, and disease stability. If your hyperthyroidism is well-controlled, Mounjaro may be safe — however, this must be evaluated on a case-by-case basis. Always disclose your complete thyroid history during any consultation.
Will Mounjaro affect my thyroid medication?
Mounjaro itself does not directly affect thyroid hormones, but significant weight loss can alter how thyroid medications are metabolised, potentially affecting dosing requirements. Your GP or endocrinologist may need to monitor your thyroid function tests and adjust doses accordingly. Inform all prescribers of your thyroid medication when discussing Mounjaro.
What should I tell a prescriber about my hyperthyroidism?
Disclose: whether your hyperthyroidism is currently controlled or active, what medication you take (antithyroid drugs, beta-blockers, etc.), when you were diagnosed, whether you've had thyroid surgery or radioactive iodine, and recent thyroid function test (TFT) results if available. This information is essential for safe prescribing assessment.
How much does Mounjaro cost privately in the UK?
Private Mounjaro costs typically range from £129–£280 per month depending on your dose (2.5 mg to 15 mg weekly). Prices vary between prescribers and pharmacies. Starting doses (2.5 mg) are generally less expensive than maintenance doses (10–15 mg). Some providers offer subscription discounts if you commit to ongoing treatment.
What's the difference between NHS and private Mounjaro access?
NHS access requires GP referral to specialist services and may involve waiting lists; private access is faster but costs money. Both require a prescription from a licensed UK prescriber. NHS prescribers may be more cautious with complex conditions like hyperthyroidism, while private prescribers must still conduct thorough clinical assessment. Neither route assures prescription — assessment depends on your individual health profile.
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