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
What Do Weight Loss Injections Do?
Weight loss injections are prescription-only medicines that help manage body weight by reducing appetite and supporting feelings of fullness. These medications, known as GLP-1 receptor agonists, work by mimicking a natural hormone your body produces after eating. In the UK, they're prescribed as part of a structured weight management programme alongside lifestyle changes. They're not a standalone solution, but clinical evidence shows they may help people lose a significant amount of weight when combined with a reduced-calorie diet and increased physical activity. Individual results vary considerably.
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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.
How Weight Loss Injections Work
Weight loss injections activate the GLP-1 hormone pathway in your body. GLP-1 is a natural gut hormone that signals fullness to your brain, slows how quickly food leaves your stomach, and helps regulate blood sugar levels. The injections amplify these effects, which may help you:
- Feel fuller after eating smaller portions
- Reduce cravings between meals
- Eat less without feeling deprived
- Experience more stable energy levels
The most commonly prescribed weight loss injections in the UK are Wegovy (semaglutide), a once-weekly injection with doses from 0.25 mg to 2.4 mg, and Mounjaro (tirzepatide), which works on two hormone pathways (GIP and GLP-1) and reaches a maximum dose of 15 mg weekly. Both are prescription-only and require a clinical assessment before being prescribed.
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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.
Weight Loss Results and NHS Access
Clinical trials show that weight loss injections may help people lose an average of 14–21% of their body weight over several months, though individual results vary significantly. This level of weight loss typically requires consistent use alongside dietary changes and physical activity. In the UK, these medications are available through NHS specialist weight management services (though waiting lists vary by region and availability can be limited) or through private prescribing following an online clinical assessment. Try our GLP-1 weight loss calculator to estimate potential outcomes at different doses, and use our BMI calculator to check your starting point for weight management discussions with your GP.
- 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 weight loss injections safe?
Weight loss injections are prescription-only medicines approved by UK and international regulators. Like all medicines, they can cause side effects — commonly nausea, diarrhoea, and constipation, especially when starting or increasing doses. A prescriber will assess whether they're suitable for your individual health. Always report any concerning symptoms to your healthcare provider.
Do weight loss injections work for everyone?
Results vary significantly between individuals. Clinical trials show average weight loss of 14–21%, but some people lose more, others less. Effectiveness depends on dose, consistency of use, adherence to dietary changes, activity levels, and individual metabolism. Your prescriber can discuss realistic expectations for you.
Can I get weight loss injections on the NHS?
Yes, weight loss injections are available through NHS specialist tier 3 weight management services in some areas. However, access varies significantly by region and waiting lists can be lengthy. Your GP can refer you to your local specialist service. Private prescribing is also available following an online clinical assessment.
What's the difference between Wegovy and Mounjaro?
Both are prescription-only weight management injections. Wegovy (semaglutide) is a GLP-1 agonist with a maximum dose of 2.4 mg weekly. Mounjaro (tirzepatide) activates two hormone pathways (GIP and GLP-1) with a maximum dose of 15 mg weekly. Mounjaro showed slightly higher average weight loss in trials, but individual response varies. Your prescriber will recommend the most appropriate option.
What happens if I stop taking weight loss injections?
Weight loss effects typically plateau once you stop the injections. Some people may gradually regain weight over time without continued use and lifestyle maintenance. This is why weight loss injections work best alongside sustained dietary changes and physical activity. Your prescriber can advise on long-term management strategies.
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.