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 Thyroid Health — What UK Adults Need to Know
Mounjaro (tirzepatide) is a prescription-only weight management injection licensed in the UK. Many people wonder about its effects on thyroid function, especially those with existing thyroid conditions. This guide explains what the evidence shows about Mounjaro and thyroid health, how to access it safely through the NHS or private prescribing, and what you need to know before starting treatment. Always consult your GP before beginning any new medication, particularly if you have a thyroid condition.
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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, Thyroid Function, and What the Evidence Shows
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist that works by mimicking natural hormones to help regulate appetite and support weight management. The drug does not directly affect thyroid hormone production, but weight loss itself can influence thyroid function slightly. Some people taking GLP-1 medications like tirzepatide report changes in thyroid-related symptoms—particularly energy levels and metabolism—though these often reflect the effects of weight loss rather than direct thyroid action. Clinical trials have not identified Mounjaro as causing thyroid disease or dysfunction in otherwise healthy individuals. However, people with existing thyroid conditions (such as thyroiditis or a history of medullary thyroid carcinoma) should not take Mounjaro. Your prescriber will assess your medical history, including any thyroid disorders, during the clinical consultation. If you have Graves' disease, Hashimoto's thyroiditis, or take levothyroxine, inform your healthcare provider before starting Mounjaro. Regular monitoring by your GP is recommended when starting weight loss medication, especially if you have an existing endocrine condition.
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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.
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Accessing Mounjaro in the UK — NHS vs Private Routes
NHS access: Mounjaro is available through specialist tier 3 weight management services following NICE approval. You'll need a GP referral, and access varies significantly by region. Waiting times can be lengthy—sometimes several months to over a year in some areas. Private access: Available through online consultations with UK-licensed prescribers. A clinician will review your health history, including thyroid function, before issuing a prescription. Private prescriptions are dispensed by GPhC-registered pharmacies. Costs typically range from £129–£320 per month depending on your dose. Whether you access Mounjaro privately or through the NHS, your prescriber will confirm it's safe for you before proceeding. Use our free BMI calculator above to check your eligibility, and our GLP-1 weight loss calculator to estimate potential outcomes at different doses.
- 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.
Does Mounjaro affect thyroid function or thyroid medication absorption?
Mounjaro does not directly alter thyroid hormone production. However, it may slow the absorption of oral medications, including levothyroxine (thyroid replacement therapy), due to delayed stomach emptying. If you take thyroid medication, inform your prescriber—dose timing adjustments may be needed to maintain stable levels.
Can I take Mounjaro if I have Hashimoto's thyroiditis or Graves' disease?
Mounjaro is not recommended if you have a history of medullary thyroid carcinoma. For other thyroid conditions like Hashimoto's or Graves' disease, discuss this with your GP or prescriber. If your condition is well-controlled on medication, Mounjaro may be considered, but careful monitoring is essential.
What is the cost of Mounjaro on the NHS in the UK?
If prescribed through an NHS specialist weight management service, Mounjaro is provided free. However, NHS access is limited and subject to local availability. Waiting lists vary; some regions have longer delays than others. Your GP can refer you to your local tier 3 service.
How does Mounjaro compare to Wegovy for people with thyroid conditions?
Both Mounjaro (tirzepatide) and Wegovy (semaglutide) are GLP-1-based medications with similar thyroid considerations. Neither directly causes thyroid disease. The main difference is mechanism: Mounjaro is a dual GIP/GLP-1 agonist, while Wegovy is GLP-1 only. Clinical trial results show Mounjaro achieved slightly higher average weight loss, though individual results vary significantly.
What should I tell my GP or prescriber about my health before starting Mounjaro?
Always disclose any history of thyroid disease, thyroid cancer, endocrine disorders, current thyroid medication, family history of medullary thyroid carcinoma, pancreatitis, gallbladder disease, severe digestion problems, or pregnancy plans. A thorough health assessment ensures Mounjaro is safe and appropriate for you.
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