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
Weight Loss Trials — What the Clinical Evidence Shows
Weight loss trials are carefully controlled clinical studies that test whether medications and treatments actually work and are safe. Several major trials have examined prescription weight loss medications available in the UK, including semaglutide (Wegovy) and tirzepatide (Mounjaro). These trials provide important evidence about how much weight people may lose, what side effects to expect, and who might benefit from treatment. Understanding what trials show helps you make informed decisions about weight management UK options with your GP.
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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.
The Major Weight Loss Trials — Key Evidence
The most significant weight loss trials have tested GLP-1 medications now available for prescription weight loss UK. The STEP trials examined semaglutide (Wegovy), showing average weight loss of approximately 14.9% of body weight over 68 weeks when combined with diet and exercise. The SURMOUNT trials tested tirzepatide (Mounjaro), a dual GIP/GLP-1 medication, demonstrating average weight loss ranging from 15% to 21% depending on dose.
- STEP-1 trial: Wegovy 2.4 mg showed ~clinically studied weight loss average at 68 weeks
- SURMOUNT-1 trial: Mounjaro 15 mg showed ~clinically studied weight loss average at 72 weeks
- Individual results vary: Some participants lost more, some less — trials report averages
- Lifestyle required: All trials combined medication with reduced-calorie diet and physical activity
These weight loss medication nhs options are now available in the UK through specialist services and private prescribing. Trial data forms the basis of how these medications are prescribed today.
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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.
Understanding Trial Results and Real-World Weight Loss
Weight loss trial results represent what happens on average in carefully controlled conditions with regular support and monitoring. Real-world outcomes may vary — some people achieve more weight loss, others less. Trials also show that continuing the medication is essential; weight often returns if treatment stops. Importantly, bmi weight loss improvements in trials translated to meaningful health benefits including improved blood sugar control and reduced cardiovascular risk factors.
If you're considering prescription weight loss treatment, calculate your personal BMI first using our free BMI calculator to understand your starting point. Then discuss with your GP whether nhs weight loss services or private prescription options might be appropriate for you. Our GLP-1 weight loss calculator can help estimate potential results at different doses.
- 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 do weight loss trials actually measure?
Clinical trials measure weight loss percentage, side effects, health improvements (like blood sugar and cholesterol changes), and how long results last. Trials also track safety data and compare medication to placebo. UK trials follow NHS standards and are reviewed by independent ethics committees before starting.
How much weight did people lose in the major trials?
In the STEP trial, Wegovy users lost on average 14.9% of body weight. In SURMOUNT trials, Mounjaro users lost 15–21% depending on dose. These are averages — individual results vary significantly. All trials combined medication with diet changes and increased physical activity.
Are trial results the same as real-world weight loss?
Trial results represent weight loss in controlled conditions with regular clinic visits and support. Real-world outcomes may differ because not everyone adheres to lifestyle changes or medication consistently. However, studies from routine NHS practice show similar results to clinical trials.
Can I access medications tested in these trials on the NHS?
Yes, Wegovy and Mounjaro are now NHS-approved for weight management. Access is through specialist tier 3/4 weight management services. Availability varies by region and waiting lists can be lengthy. Your GP can refer you, or you can explore private options through licensed UK prescribers.
Do weight loss trials measure side effects?
Yes, all major trials carefully document side effects. Common ones include nausea, diarrhoea, and constipation — usually mild to moderate and improving over time. Serious side effects are rare but monitored. Your prescriber will discuss potential side effects before starting treatment. ```
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.