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
Mounjaro and Graves Disease — What UK Patients Need to Know
If you have Graves disease or thyroid concerns and are considering weight loss treatment, it's important to understand how Mounjaro (tirzepatide) may interact with your condition. Graves disease is an autoimmune thyroid condition that requires careful management, and prescription weight loss medications need specialist assessment. This guide explains the key considerations, how Mounjaro compares to Wegovy, and why individual clinical assessment is essential before starting any GLP-1 or GIP/GLP-1 medication if you have thyroid disease.
10,000+ calculations today · NHS-aligned thresholds · 100% free
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.
Mounjaro, Wegovy, and Thyroid Health — Mechanism and Trial Data
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist — it activates two natural hormone pathways. Wegovy (semaglutide) is a GLP-1 receptor agonist only, activating a single pathway. In clinical trials, Mounjaro showed average weight loss of around 20.9% of body weight at maximum dose (15 mg), whilst Wegovy showed approximately 14.9% at maximum dose (2.4 mg) in the STEP-1 trial, though individual results vary significantly.
Both medications slow gastric emptying and may affect how the gut processes food and nutrients. For people with Graves disease, thyroid function and medication absorption are particularly important considerations. Neither medication directly affects thyroid hormone levels, but both may influence gut motility and nutrient absorption — factors your GP or endocrinologist must assess, especially if you take levothyroxine or other thyroid medications. The tirzepatide formulation and dosing schedule differ: Mounjaro uses a KwikPen with doses from 2.5 mg to 15 mg once weekly, escalating over 16+ weeks.
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.
Graves Disease and GLP-1 Treatment — Clinical Considerations and Prescriber Assessment
Graves disease alters how your body metabolises nutrients and manages blood glucose and energy regulation. Some GLP-1 medications may theoretically worsen or mask certain symptoms of thyroid disease, or interact with thyroid replacement therapy absorption. This is why specialist clinical assessment is essential before starting Mounjaro or Wegovy if you have thyroid disease.
Your prescriber will need to know: your current thyroid function (TSH, free T4 levels), any thyroid medications you take, how well-controlled your Graves disease is, and whether you've experienced any complications. Neither Mounjaro nor Wegovy is absolutely contraindicated in Graves disease, but both require careful individual evaluation by someone familiar with your thyroid history. Use our free GLP-1 weight loss calculator to estimate potential outcomes, but always discuss thyroid-specific risks with your GP or endocrinologist before proceeding. A full thyroid function test may be recommended before and during treatment.
- 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 Graves disease?
Mounjaro is not absolutely contraindicated in Graves disease, but it requires specialist clinical assessment. Your GP or endocrinologist must evaluate your thyroid function, current medications (especially levothyroxine), disease control, and individual risk factors. Never start Mounjaro without discussing your Graves disease diagnosis with your prescriber.
Does Mounjaro affect thyroid hormone levels?
Mounjaro does not directly alter thyroid hormone production. However, it may slow gastric emptying, which could theoretically affect the absorption of thyroid medications like levothyroxine. Your prescriber may recommend thyroid function tests before and during treatment to monitor this interaction.
Is Wegovy safer than Mounjaro for Graves disease?
Both Wegovy and Mounjaro require individual clinical assessment if you have Graves disease. Neither is definitively "safer" — the choice depends on your specific thyroid history, disease control, current medications, and prescriber judgment. Both are GLP-1-based medications with similar absorption and motility effects.
What should I tell my prescriber about my Graves disease?
Inform your prescriber of: your Graves disease diagnosis, current thyroid function test results (TSH and free T4), any thyroid medications you take, how long you've had Graves disease, whether you've had treatment (radioactive iodine, surgery, or antithyroid drugs), and any current symptoms or complications. This helps them assess suitability.
Will I need thyroid function tests if I start Mounjaro?
Yes, most prescribers recommend baseline thyroid function testing before starting Mounjaro if you have Graves disease, and repeat tests during treatment. This monitors for any medication interactions or changes in thyroid control. Your GP can arrange these tests as part of your weight management care plan.
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.