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
Safe Weight Loss Supplements in the UK
When it comes to weight management in the UK, the safest and most effective supplements are prescription-only medications prescribed by a licensed healthcare professional following a clinical assessment. The NHS recommends evidence-based weight loss medication alongside lifestyle changes as part of structured weight management programmes. Non-prescription supplements lack the robust safety and efficacy data of approved prescription treatments, making prescription options the gold standard for those who qualify. Understanding your options and eligibility is the first step towards sustainable weight loss.
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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.
Prescription Weight Loss Medication — The Safest Evidence-Based Option
In the UK, prescription weight loss medications are the most rigorously tested and safest supplement options available for weight management. The two main prescription injections licensed for weight loss are Mounjaro (tirzepatide) and Wegovy (semaglutide). Both are GLP-1 (or GIP/GLP-1) receptor agonists that work by regulating appetite and food cravings. Clinical trials showed these medications may help adults lose an average of 15–21% of their body weight when used alongside a reduced-calorie diet and increased physical activity — though individual results vary significantly.
To access prescription weight loss medication in the UK, you typically need to meet specific criteria: a BMI of 30 or above, or a BMI of 27–29.9 with weight-related health conditions such as type 2 diabetes, high blood pressure, or sleep apnoea. Your GP can assess your eligibility and either refer you to NHS specialist weight management services or you can seek a prescription through an online clinical assessment with a UK-licensed prescriber. Always ensure any prescriber is registered with the General Pharmaceutical Council (GPhC).
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.
Why Non-Prescription Weight Loss Supplements Are Less Reliable
Over-the-counter weight loss supplements — including herbal products, vitamins, and dietary supplements — typically lack the extensive safety testing and clinical trial data of prescription medications. The UK Medicines and Healthcare products Regulatory Agency (MHRA) does not regulate food supplements as rigorously as prescription drugs, meaning efficacy claims are often unproven and side effects may not be well-documented. Many non-prescription supplements make exaggerated weight loss claims that are not supported by evidence.
For sustainable, medically-supervised weight management, the NHS recommends focusing on prescription weight loss medication combined with lifestyle changes. Try our free BMI calculator to check your current BMI and understand your starting point, and use our GLP-1 weight loss calculator to see potential outcomes if prescription medication is 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.
Are prescription weight loss injections safe?
Yes — Mounjaro and Wegovy are licensed by the MHRA and have undergone extensive clinical trials. Like all medications, they have potential side effects (nausea, diarrhoea, constipation are most common), which are monitored by your prescriber. Your clinical assessment ensures the medication is safe for your individual health profile. Always discuss risks and benefits with your GP or licensed prescriber.
How do I access safe weight loss supplements on the NHS?
Ask your GP for a referral to your local specialist weight management service (tier 3). NHS access varies significantly by region and waiting lists can be long in some areas. Some regions now offer tirzepatide or semaglutide through NHS services, though availability is still limited. Your GP can advise on local options.
What's the difference between Mounjaro and Wegovy?
Both are prescription weight loss injections, but they work differently. Mounjaro (tirzepatide) is a dual GIP and GLP-1 agonist and may help slightly more weight loss (average 15–21% body weight). Wegovy (semaglutide) is a GLP-1 agonist only (average ~15% body weight). Both require prescription and clinical assessment. Your prescriber will recommend the most suitable option for you.
Can I buy weight loss supplements over the counter in the UK?
Yes, many supplements are available without prescription, but they lack the rigorous testing and clinical evidence of prescription medications. Most non-prescription supplements have not been proven effective in large trials. For evidence-based weight loss support, prescription options monitored by a healthcare professional are significantly safer and more reliable.
What eligibility criteria do I need to meet for prescription weight loss medication?
You typically need a BMI of 30 or above, or 27–29.9 with weight-related health conditions (type 2 diabetes, hypertension, sleep apnoea, cardiovascular disease). For South Asian, Chinese, Black African, or Black Caribbean adults, lower BMI thresholds may apply. A prescriber will assess your individual health during your clinical assessment to confirm eligibility.
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.