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
Will Thyroxine Cause Weight Loss?
Thyroxine (levothyroxine) is a prescription thyroid replacement hormone used to treat hypothyroidism. It doesn't directly cause weight loss, but correcting a thyroid deficiency may help normalise metabolism and support healthy weight management. If you're struggling with weight despite adequate thyroid treatment, UK-licensed prescription weight management options are available for eligible adults. Your GP can assess which approach is right for you.
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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.
Thyroxine, Thyroid Function, and Weight
Thyroxine is not a weight loss medication. It's prescribed to replace thyroid hormone (T4) in people with hypothyroidism — a condition where the thyroid doesn't produce enough hormone naturally. When thyroid levels are too low, metabolism slows, which can contribute to weight gain.
Taking thyroxine restores thyroid hormone to a healthy level, which helps your metabolism return to normal. This may support gradual weight loss, but thyroxine won't cause rapid or significant weight loss on its own. The amount of weight change depends on how deficient you were, your age, activity level, and diet.
- Correct dosing matters: Your GP will adjust your thyroxine dose based on TSH blood tests. Being over-medicated (too much thyroxine) can cause anxiety, palpitations, and muscle weakness.
- Weight loss takes time: Once thyroid function is stable, sustainable weight management typically requires calorie reduction and physical activity.
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.
UK Weight Management Options for Eligible Adults
If you've had your thyroid properly a UK pharmacy but still find weight management difficult, several prescription weight loss options are available in the UK for eligible adults. These include Mounjaro (tirzepatide), Wegovy (semaglutide), and Saxenda (liraglutide) — all licensed GLP-1 or dual GIP/GLP-1 receptor agonist injections. Eligibility depends on your BMI and any weight-related health conditions.
Access is through either NHS specialist tier 3 weight management services (via GP referral) or private prescription following an online clinical assessment. Try our free GLP-1 weight loss calculator to explore potential outcomes, and use our BMI calculator to check your personal BMI — both tools help determine eligibility and next steps with your healthcare provider.
Talk to your GP if you're concerned about your weight despite stable thyroid medication. They can check whether your thyroxine dose is correct, rule out other medical causes of weight gain, and discuss whether prescription weight management treatment might be appropriate. Use our free weight converter to track your weight consistently in stone or kilograms — consistent monitoring helps your GP assess progress and adjust your plan. NHS weight management services are available in most areas, though waiting times vary by region.
- 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 thyroxine help you lose weight?
Thyroxine isn't designed for weight loss. It corrects low thyroid hormone levels, which may help normalise metabolism and support gradual weight loss if you were hypothyroid. However, significant weight loss requires dietary changes and physical activity alongside normal thyroid function.
Can too much thyroxine cause weight loss?
Being over-medicated with thyroxine (too high a dose) can cause gradual weight management, increased heart rate, and anxiety — but this is harmful and not intentional. Your GP monitors your TSH levels to keep your dose safe and appropriate.
What if I'm still gaining weight on thyroxine?
Several reasons could explain this: your dose may need adjustment, absorption issues, other medical conditions (like polycystic ovary syndrome), or simply calorie intake exceeding expenditure. Ask your GP for a TSH test and discuss weight management strategies, including potential prescription options if you're eligible.
Are there prescription weight loss options available in the UK?
Yes. Adults with a BMI of 30 or above, or 27+ with weight-related health conditions, may be eligible for prescription weight loss injections like Mounjaro or Wegovy. These are available through NHS specialist services or private prescription following clinical assessment.
How do I find out if I'm eligible for NHS weight management treatment?
Start by speaking to your GP. They can check your BMI, assess your health, and refer you to your local NHS tier 3 specialist weight management service if appropriate. Availability and waiting times vary by region, but most areas have services available.
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.