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 Side Effects and Thyroid Health
Mounjaro (tirzepatide) is a prescription-only GLP-1 and GIP receptor agonist licensed in the UK for weight management. One concern patients often have is whether this medication affects thyroid function. While thyroid-related side effects are not listed as common effects of Mounjaro in clinical trials, thyroid health monitoring is important for anyone considering this treatment. This guide explains what the evidence shows, what to monitor, and how to access Mounjaro safely in the UK through both NHS specialist services and private prescription routes.
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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.
Thyroid Effects and Safety Monitoring
Clinical trials of Mounjaro (tirzepatide) did not identify thyroid dysfunction as a common side effect. However, because Mounjaro affects how your body processes energy and metabolism, some patients and healthcare providers recommend baseline thyroid screening before starting treatment. This is particularly important if you have a personal or family history of thyroid disease.
What the evidence shows:
- Thyroid disorders were not reported as frequent adverse events in SURMOUNT trials
- gradual weight management itself can sometimes affect thyroid hormone levels
- Any GLP-1 medication may slightly alter thyroid hormone requirements in patients already on thyroid replacement therapy
- Your GP or prescriber should check your thyroid function (TSH and free T4) before starting, especially if you have a history of thyroid problems
If you take levothyroxine or other thyroid medication, inform your prescriber before starting Mounjaro, as dose adjustments may be needed over time.
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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.
Accessing Mounjaro in the UK — Cost and Routes
NHS Access: Mounjaro is now approved by NICE for use within specialist tier 3 and tier 4 weight management services. Access is through your GP referral to a specialist weight management clinic. Waiting times vary significantly by region, and availability depends on your local Integrated Care Board (ICB) commissioning.
Private Prescription Access: You can also obtain a Mounjaro prescription privately through an online clinical consultation with a UK-licensed prescriber. Private consultations typically cost £50–£150, and medication costs range from approximately £129–£250 per month depending on your dose. A private prescriber will assess your eligibility, including thyroid history, before issuing a prescription to a GPhC-registered pharmacy. This route avoids NHS waiting lists but requires you to pay for all consultations and medication.
Use our free BMI calculator above to check your starting point, and our GLP-1 weight loss calculator to explore potential outcomes at different Mounjaro doses alongside your healthcare plan.
What to Expect During Assessment: Whether you pursue NHS or private prescription, your prescriber will review your medical history, current medications (including any thyroid medication), and conduct baseline health checks. You'll receive education on injection technique, diet, and physical activity. Private consultations are typically completed online within 24–48 hours; NHS referrals can take weeks to months depending on local waiting lists.
Monitoring After Starting: Once on Mounjaro, you'll have regular follow-ups (usually every 4 weeks during dose escalation, then every 12 weeks once stable). If you're on thyroid medication, your GP may recommend repeat TSH checks after 6–12 weeks on Mounjaro to ensure your dose remains appropriate. Always report any symptoms like unusual fatigue, temperature sensitivity, or mood changes to your healthcare provider.
- 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 cause thyroid problems?
Thyroid dysfunction was not reported as a common side effect in Mounjaro clinical trials. However, gradual weight management can sometimes affect thyroid hormone levels, and if you're on thyroid replacement therapy, your dose may need adjustment. Baseline thyroid screening before starting is recommended, especially if you have thyroid history.
Do I need thyroid tests before starting Mounjaro?
It's prudent to have baseline thyroid function tests (TSH and free T4) checked before starting, particularly if you have a personal or family history of thyroid disease or are taking thyroid medication. Your GP or private prescriber should discuss this during your assessment.
How much does a Mounjaro prescription cost privately in the UK?
Private Mounjaro consultations typically cost £50–£150. Medication costs depend on your dose: starting doses around £129–£180 per month, with higher doses (10–15 mg) ranging from £200–£250 per month. Prices vary between private prescribing providers.
How long does it take to get Mounjaro on the NHS?
NHS access requires a GP referral to a specialist weight management service. Waiting times vary greatly by region—some areas may take several weeks, others several months. Your local Integrated Care Board (ICB) determines availability and waiting lists.
What's the difference between NHS and private access to Mounjaro in the UK?
NHS access is free but involves waiting lists and referral requirements. Private prescription allows faster access (typically 24–48 hours) but costs approximately £129–£250 per month for medication plus consultation fees. Both routes require clinical assessment and prescription from a licensed prescriber.
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.