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
Best Thyroid Supplement for Weight Loss — What the Evidence Shows
If you're searching for the best thyroid supplement for weight loss, it's important to understand that thyroid supplements alone are not a proven weight loss solution. Thyroid function does affect metabolism and weight, but the relationship is more complex than many supplement claims suggest. This guide explains how your thyroid impacts weight, what evidence actually supports, and the evidence-based approaches to weight management in the UK — including prescription options where appropriate.
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.
Does Thyroid Function Really Affect Weight?
Yes, your thyroid plays a genuine role in metabolism. The thyroid produces hormones that regulate how fast your body burns calories (metabolic rate). If your thyroid is underactive (hypothyroidism), your metabolism slows, potentially leading to weight gain. If it's overactive (hyperthyroidism), you may lose weight unintentionally.
However, thyroid disorders account for only a small percentage of weight gain in the UK population. According to NHS guidance, thyroid problems explain weight changes in only about 5–10% of people seeking weight management. Most weight gain is driven by calorie intake, physical activity levels, genetics, and other hormonal factors. If you suspect your thyroid is contributing to weight gain, your GP can test your thyroid function (TSH and free T4 levels) — this is a simple blood test and is the right first step.
If your thyroid is normal and functioning well, thyroid supplements will not boost weight loss. Taking extra thyroid hormone when your thyroid is healthy is not safe and can cause serious side effects including heart problems and bone loss.
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.
What About Thyroid Supplements — Do They Work for Weight Loss?
The evidence for thyroid supplements as a weight loss tool is weak. Common thyroid supplements include iodine, selenium, zinc, and L-tyrosine. While these nutrients are essential for thyroid function, studies have not shown that taking them in supplement form helps people without thyroid deficiency lose weight. The NHS does not recommend thyroid supplements specifically for weight loss.
If you have a diagnosed thyroid condition (like hypothyroidism), appropriate thyroid medication — prescribed by your GP — is the right treatment. For weight management alongside normal thyroid function, evidence-based approaches include balanced nutrition, calorie awareness, and physical activity. If diet and lifestyle changes alone are not working, prescription weight loss medications such as GLP-1 injections (Wegovy or Mounjaro) have strong clinical evidence and are available in the UK through NHS specialist services or private prescribing. These are prescription-only medications requiring clinical assessment — they work through a different mechanism than thyroid support.
- 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 thyroid supplements help me lose weight if my thyroid is normal?
No. If your thyroid function is normal, taking thyroid supplements will not support weight loss and may cause harm. Weight loss is best achieved through calorie management, physical activity, and — if appropriate — prescription weight loss medication prescribed following clinical assessment by your GP or a licensed prescriber.
How do I know if my thyroid is affecting my weight?
If you suspect thyroid problems, ask your GP for a blood test measuring TSH and free T4 levels. This simple test confirms whether your thyroid is functioning normally. Many people assume thyroid issues are causing weight gain when other factors (calorie intake, activity, genetics, medications) are actually responsible. Your GP can help clarify this.
Are thyroid supplements safe to take with weight loss medication?
Thyroid supplements are generally safe if you have a diagnosed deficiency, but always inform your GP or prescriber of any supplements you're taking — including iodine, selenium, or any "thyroid support" products. Some supplements can interact with prescription medications. Your prescriber needs a complete picture of what you're taking.
What prescription weight loss options are available in the UK if thyroid isn't the issue?
If your thyroid is normal and you meet eligibility criteria, prescription weight loss medications such as Wegovy (semaglutide) and Mounjaro (tirzepatide) are available. These GLP-1 and GIP/GLP-1 receptor agonists are licensed for weight management in UK adults with a BMI of 30 or above, or 27 or above with weight-related health conditions. Use our GLP-1 weight loss calculator to explore potential outcomes, and discuss options with your GP.
Should I take supplements if I have hypothyroidism and want to lose weight?
If you have diagnosed hypothyroidism, your GP will prescribe appropriate thyroid medication (usually levothyroxine). Discuss any supplements you wish to take with your GP first — some can interfere with thyroid medication absorption. Weight loss with hypothyroidism should focus on balanced nutrition, activity, and — if suitable — prescription weight loss medication, not supplements alone.
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.