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
Thyroid Medicine and Weight Loss — What You Need to Know
Thyroid conditions can affect your weight, and some thyroid medications may influence weight loss efforts. However, if you're seeking prescription weight management in the UK, several licensed options are available beyond thyroid-related treatments. This guide explains how thyroid health relates to weight, and outlines the prescription weight loss medications currently approved for eligible UK adults, including how to access them through the NHS or privately.
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.
UK-Licensed Prescription Weight Loss Medications
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 management in the UK. The main licensed options are:
- Mounjaro (tirzepatide) — a once-weekly injection that acts as a dual GIP and GLP-1 receptor agonist. Clinical trials showed average weight loss of approximately 15–21% of body weight over 72 weeks, though individual results vary.
- Wegovy (semaglutide) — a once-weekly GLP-1 injection. Clinical evidence suggests average weight loss of around 14.9% of body weight, used alongside a reduced-calorie diet and increased physical activity.
- Saxenda (liraglutide) — a daily GLP-1 injection, an earlier licensed option for weight management in the UK.
All three are prescription-only and require clinical assessment before being prescribed. Use our free BMI calculator above to check whether you may be in the eligible range, and our GLP-1 weight loss calculator to explore potential outcomes at different doses.
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 — How to Get Started
Access to prescription weight loss medication in the UK follows two routes:
- NHS route: Referral to a tier 3 specialist weight management service through your GP. Availability varies significantly by region, and waiting lists can be lengthy. Not all ICBs currently commission these services.
- Private route: Online consultation with a UK-licensed prescriber. If clinically appropriate, a prescription is issued and dispensed by a GPhC-registered pharmacy. No NHS referral required.
Your GP can assess your individual circumstances and discuss which option is most suitable for you. If thyroid medication is affecting your weight, your GP can also explore whether adjustments to your thyroid treatment may help, as part of a holistic weight management approach.
Weight management in the UK is increasingly recognised as important for long-term health. If you're taking thyroid medication and concerned about weight, speak to your GP. They can review your thyroid medication, discuss your weight health context using tools like our free weight converter and BMI calculator, and explore whether prescription weight loss medication might be appropriate. Even modest weight loss of 5–10% of body weight can bring meaningful health benefits. Your prescriber will assess your individual eligibility and health needs — results vary between individuals, and all weight management is most effective when combined with sustained lifestyle changes.
- 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 medication cause weight gain?
Yes, some thyroid medications or underactive thyroid (hypothyroidism) can contribute to weight gain. If you're taking thyroid medication and gaining weight, discuss this with your GP — your dose may need adjusting, or there may be other factors at play. Your GP can help determine the cause and explore options.
Is prescription weight loss medication available on the NHS in the UK?
Yes, Mounjaro, Wegovy, and Saxenda are available through NHS specialist tier 3 weight management services for eligible adults. However, availability and waiting times vary significantly by region. Your GP can refer you if you meet eligibility criteria (typically BMI 30 or above, or 27–29.9 with weight-related conditions).
What is the difference between Mounjaro and Wegovy?
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist, while Wegovy (semaglutide) is a GLP-1 agonist only. In clinical trials, Mounjaro showed slightly higher average weight loss (15–21% vs 14.9% for Wegovy), but individual results vary. Both are once-weekly injections prescribed privately or through NHS services.
How quickly can I expect to lose weight on prescription medication?
Weight loss typically begins within the first few weeks and continues gradually over several months. Safe weight loss is generally 0.5–1 kg per week. Clinical trials showed significant results over 68–72 weeks. Individual results vary, and medication works best alongside a reduced-calorie diet and increased physical activity.
Do I need a referral from my GP to access private prescription weight loss medication?
No — you can access private prescription weight loss medication through an online consultation with a UK-licensed prescriber without a GP referral. However, your GP should be aware of any medications you're taking. For NHS access, a GP referral to a specialist service is typically required.
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.