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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T3 Triiodothyronine and Weight Loss in the UK
T3 triiodothyronine is a thyroid hormone sometimes discussed for weight loss, but it is not licensed in the UK for weight management. If you're looking for prescription weight management options in the UK, there are several NHS-approved alternatives available. This guide explains what T3 is, why it's not used for routine weight loss, and which licensed weight loss medications you may be eligible for instead. The NHS and MHRA recommend evidence-based prescription medications for eligible adults seeking professional support with weight management.
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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.
Licensed Weight Loss Medications Available in the UK
If you have a BMI of 30 or above, or a BMI of 27–29.9 with weight-related health conditions, you may be eligible for prescription weight loss medication in the UK. The three licensed options are Mounjaro (tirzepatide), Wegovy (semaglutide), and Saxenda (liraglutide).
- Mounjaro: Once-weekly injection, dual GIP and GLP-1 agonist. Clinical trials showed average weight loss of 15–21% of body weight.
- Wegovy: Once-weekly injection, GLP-1 agonist. Average weight loss of approximately 15% of body weight in trials.
- Saxenda: Once-daily injection, GLP-1 agonist. Typically produces modest weight loss alongside lifestyle changes.
All three require a clinical assessment and prescription. They are used alongside a reduced-calorie diet and increased physical activity—not as a standalone treatment. Individual results vary significantly based on lifestyle changes, genetics, and how your body responds.
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.
How to Access Weight Loss Medication in the UK
NHS route: Speak to your GP about referral to a tier 3 specialist weight management service. Availability and waiting times vary significantly by region. Some areas have long waiting lists.
Private route: Licensed prescription weight loss medications are available through private online prescribing services. You'll complete an online clinical assessment with a UK-licensed prescriber. If approved, a prescription is sent to a GPhC-registered pharmacy. This route typically offers faster access than NHS services.
Use our free GLP-1 weight loss calculator to explore potential outcomes at different doses, and our BMI calculator to check your eligibility based on current guidelines.
- 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.
Is T3 prescribed for weight loss in the UK?
No. T3 (triiodothyronine) is a thyroid hormone used to treat hypothyroidism, not licensed for weight loss. Using T3 off-label for weight management is not recommended and can pose health risks. Licensed prescription weight loss medications like Mounjaro and Wegovy are evidence-based alternatives.
What is T3 triiodothyronine actually used for?
T3 is a thyroid hormone produced naturally by the thyroid gland. It regulates metabolism and energy production. It is prescribed only for diagnosed thyroid disorders like hypothyroidism. Misusing thyroid hormones for weight loss can cause serious side effects including heart problems and bone loss.
What are the approved alternatives to T3 for weight loss in the UK?
Three medications are licensed in the UK for weight management: Mounjaro (tirzepatide), Wegovy (semaglutide), and Saxenda (liraglutide). All are prescription-only and require clinical assessment. They work by affecting appetite regulation and are used alongside lifestyle changes.
Am I eligible for prescription weight loss medication in the UK?
You may be eligible if you have a BMI of 30 or above, or 27–29.9 with weight-related conditions like type 2 diabetes, hypertension, or sleep apnoea. Eligibility varies by ethnicity—South Asian, Chinese, and Black African/Caribbean adults have lower thresholds. Ask your GP for assessment.
How do I know which weight loss medication is right for me?
This depends on your personal health, medical history, and how your body responds. A prescriber will assess you individually during a clinical consultation. Factors include existing medications, contraindications, and treatment goals. Your GP or private prescriber will recommend the most suitable option for you.
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.