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
Can Levothyroxine Cause Weight Loss?
Levothyroxine is a thyroid hormone replacement used to treat hypothyroidism, not a weight loss medication. While correcting thyroid function may support healthy weight management, levothyroxine itself is not prescribed for weight loss. If you're looking for weight management support in the UK, prescription weight loss medications are available for eligible adults. This guide explains levothyroxine's role in weight, and explores actual prescription weight loss options available on the NHS and privately.
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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.
Weight Loss Options Available in the UK
If you're interested in weight management in the UK, there are prescription medications licensed specifically for weight loss. The most established options include Mounjaro (tirzepatide), which is a dual GIP and GLP-1 receptor agonist, and Wegovy (semaglutide), a GLP-1 agonist. Saxenda (liraglutide) is also available as a daily injection option. Clinical trials showed these medications can help adults lose an average of 14–21% of their body weight when used alongside diet and exercise changes. Our GLP-1 weight loss calculator can help you estimate potential results at different doses. All prescription weight loss medications require a clinical assessment to determine eligibility, and individual results vary significantly. These are prescribed through NHS specialist weight management services or through private consultations with UK-licensed prescribers.
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 Weight Loss Support
On the NHS, weight loss medication is available through tier 3 specialist weight management services. Your GP can refer you to a local service if you meet the criteria (typically BMI 30 or above, or BMI 27+ with weight-related health conditions). NHS access is free but waiting lists vary by region. Private access is available immediately through online prescribers following a clinical assessment—no GP referral needed. Costs typically range from £129–£320 per month depending on medication and dose. Use our free BMI calculator to check where you stand, then speak with your GP about whether prescription weight loss support might be appropriate for your individual situation.
- 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 levothyroxine help you lose weight?
Levothyroxine is not a weight loss medication. It's a thyroid hormone replacement for hypothyroidism. Once thyroid levels are properly balanced, it may support normal metabolism, but weight loss is not an expected outcome. If you've gained weight since starting levothyroxine, discuss this with your GP—your dose may need adjusting, or other factors may be at play.
What are the actual prescription weight loss medications available in the UK?
Mounjaro (tirzepatide), Wegovy (semaglutide), and Saxenda (liraglutide) are licensed for weight management in the UK. All are GLP-1 or dual GIP/GLP-1 receptor agonists—entirely different from thyroid medications. They work by helping reduce appetite and support feeling fuller on smaller portions, alongside dietary and lifestyle changes.
How do I know if I'm eligible for prescription weight loss medication?
Eligibility typically requires a BMI of 30 or above, or BMI 27–29.9 with weight-related health conditions (like type 2 diabetes, high blood pressure, or sleep apnoea). A GP or licensed prescriber assesses your individual situation. Use our BMI calculator to check your starting point, then speak with your healthcare provider.
Can I get weight loss medication on the NHS, or do I have to pay privately?
Both options exist in the UK. NHS access is through specialist tier 3 weight management services (free but with waiting lists). Private access is available immediately through online prescribers (typically £129–£320/month). Your GP can advise on NHS availability in your region and whether you meet referral criteria.
Can I take levothyroxine and weight loss medication together?
It's essential to inform any prescriber about all medications you take, including levothyroxine. Weight loss medications can affect how quickly other medicines are absorbed, so timing and doses may need adjustment. Your GP or specialist will assess whether combination use is safe for you personally.
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.