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
Does GLP-1 Work For Weight Loss?
GLP-1 medications do work for weight loss in many people — clinical trials have shown consistent results. These prescription-only injections, including Wegovy (semaglutide) and Mounjaro (tirzepatide), have been clinically proven to support weight loss when used alongside dietary changes and increased physical activity. However, results vary between individuals, and they are not a structured approach. This guide explains how GLP-1 works, what the evidence shows, and how to access weight loss medication in the UK through both NHS and private options.
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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.
How GLP-1 Medications Work For Weight Loss
GLP-1 (glucagon-like peptide-1) medications work by mimicking a natural hormone produced in your gut. When you eat, your body releases GLP-1, which tells your brain you are full and satisfied. GLP-1 receptor agonist medications amplify this signal, which means you may feel fuller after eating smaller meals and have fewer cravings between meals.
Additionally, these medications slow how quickly food leaves your stomach, which extends the feeling of fullness. Wegovy (semaglutide) is a single-action GLP-1 agonist, while Mounjaro (tirzepatide) activates both GLP-1 and GIP receptors for dual-action support. Both are prescription-only injections taken once weekly. In clinical trials, participants using these medications alongside reduced-calorie diet and increased physical activity achieved sustained weight loss over several months.
Clinically BackedWeight Loss
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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.
Clinical Evidence: What The Research Shows
Clinical trials demonstrate that GLP-1 medications do help people lose weight when used properly. The STEP-1 trial found that Wegovy helped participants lose an average of approximately 15% of their body weight over 68 weeks. Mounjaro (tirzepatide) showed average weight loss of 15–21% of body weight across the SURMOUNT trials at 72 weeks.
Important context: These results occurred alongside reduced-calorie diet and increased physical activity — the medication supports weight loss, but does not cause weight loss on its own. Individual results vary significantly, and weight loss continues as long as you take the medication. Many people regain weight if they stop taking it without maintaining 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.
Do GLP-1 injections work for everyone?
GLP-1 medications help many people lose weight, but results vary. Clinical trials show average weight loss of 15–21%, but some people lose more and some lose less. Factors affecting results include adherence to the medication, dietary changes, physical activity level, genetics, and individual metabolism. A prescriber will assess whether this medication is suitable for you based on your health.
How quickly will I lose weight with GLP-1?
Weight loss typically begins within 2–4 weeks but varies between individuals. Most people see gradual, steady loss over several months. The NHS recommends losing 0.5–1 kg per week for sustainable results. You can track your progress with our free progress tracker to monitor changes over time and see how your weight management journey develops.
Is GLP-1 weight loss available on the NHS in the UK?
Yes, tirzepatide (Mounjaro) and semaglutide (Wegovy) are available through NHS specialist tier 3 weight management services. However, NHS access requires referral from your GP and assessment by a specialist service. Availability and waiting times vary significantly by region. Your GP can discuss whether NHS specialist services are appropriate for your situation.
What happens if I stop taking GLP-1 medication?
Weight loss from GLP-1 medications is typically sustained only while taking the medication. If you stop without maintaining the dietary and lifestyle changes that supported your weight loss, weight regain is common. These medications are tools to help you develop healthier habits — they work best alongside lasting changes to diet and physical activity.
Can I use our GLP-1 weight loss calculator to estimate my results?
Yes — our free GLP-1 weight loss calculator can help you explore projected weight loss at different doses based on clinical trial averages. Remember, individual results vary significantly, and the calculator shows estimates only. Use it alongside our free BMI calculator to understand your starting point and healthy weight range for your height. ```
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.