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
T3 and Weight Loss — Understanding UK Prescription Options
T3 (liothyronine) is a prescription thyroid hormone medication, not a primary weight loss treatment. However, if you're looking for effective weight management in the UK, prescription medications specifically licensed for weight loss are now available. This guide explains UK-approved weight loss options, who is eligible, and how to access them through both NHS and private routes.
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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.
UK-Licensed Weight Loss Medications — What's Available
If you're exploring prescription weight loss medication in the UK, three main options are licensed by the MHRA for weight management:
- Mounjaro (tirzepatide) — a once-weekly injection that acts as a dual GIP and GLP-1 receptor agonist, helping regulate appetite and support feelings of fullness
- Wegovy (semaglutide) — a once-weekly GLP-1 injection licensed specifically for weight management, separate from its diabetes formulation
- Saxenda (liraglutide) — a daily GLP-1 injection, an earlier approved option for weight management
In clinical trials, these medications helped participants lose an average of 14–21% of their body weight when combined with reduced-calorie diet and increased physical activity — though individual results vary significantly. You can estimate potential weight loss with our GLP-1 weight loss calculator to see projected outcomes at different doses. All are prescription-only medicines requiring clinical assessment before prescribing.
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.
NHS vs Private Access — Finding the Right Route for You
Access to prescription weight loss medication in the UK depends on your route:
- NHS: Available through specialist tier 3 weight management services following GP referral. Eligibility and availability vary significantly by region. Waiting times can be lengthy in many areas.
- Private: Available through online consultations with UK-licensed prescribers. No NHS referral required. Costs vary by dose and provider (typically £129–£320 monthly).
To find out if you're eligible, discuss your weight management and health goals with your GP. Use our free BMI calculator to check your current BMI and understand your health context — your GP can then advise whether prescription options are appropriate for you.
- 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.
What is T3 and does it help with weight loss?
T3 (liothyronine) is a prescription thyroid hormone used to treat thyroid conditions like hypothyroidism. It is not licensed for weight loss. However, if thyroid function is low, correcting it with appropriate medication may support metabolism. Always discuss thyroid concerns with your GP.
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 health conditions (diabetes, high blood pressure, sleep apnoea, heart disease). Eligibility is assessed individually by a prescriber. Your GP can advise on NHS access or private options.
How much weight can I expect to lose with Mounjaro or Wegovy?
Clinical trials showed average weight loss of 14–21% body weight over 68–72 weeks alongside diet and exercise changes. Individual results vary significantly based on dose, adherence, and personal factors. Results are not assured.
Can I get weight loss injections on the NHS?
Yes. Mounjaro and Wegovy are available through NHS specialist weight management services in some areas. Access varies by region and ICB. Ask your GP about referral to tier 3 weight management services. Waiting times can be several months to years in some areas.
What's the difference between Wegovy and Ozempic?
Both contain semaglutide, but Wegovy is licensed for weight management in the UK at doses up to 2.4mg. Ozempic is licensed for type 2 diabetes at doses up to 2mg and is not approved for weight loss in the UK. Using Ozempic for weight loss would be off-label.
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.