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
How Glucagon-Like Peptide Supports Weight Loss
Glucagon-like peptide (GLP-1) is a natural hormone that regulates appetite and blood sugar. GLP-1 receptor agonist medications mimic this hormone to support weight management in UK adults. Prescription-only injections like Wegovy use this mechanism to help reduce hunger, support feeling fuller after meals, and assist with sustainable weight loss alongside lifestyle changes. This guide explains how GLP-1 weight loss works, who may be eligible, and what to expect. Our free GLP-1 weight loss calculator can help you estimate potential results at different doses.
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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 receptor agonists activate the body's natural GLP-1 hormone pathway, which plays a crucial role in appetite regulation. When you take a GLP-1 weight loss medication like Wegovy (semaglutide), it signals to your brain that you are fuller, helping reduce cravings and overeating. The medication also slows how quickly food leaves your stomach, meaning you feel satisfied after smaller portions.
- Reduces appetite: Signals to the brain to decrease hunger signals
- Slows gastric emptying: Food moves through your digestive system more slowly, extending fullness
- Supports blood sugar control: Helps regulate glucose, reducing energy crashes that trigger cravings
- Works with lifestyle changes: Most effective when combined with a reduced-calorie diet and increased physical activity
In clinical trials, including the STEP-1 study, Wegovy helped participants lose an average of approximately 15% of their body weight over 68 weeks, though individual results vary significantly. Weight loss success depends on prescription dose, adherence, diet quality, and exercise consistency.
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.
UK Eligibility and Access Routes
In the UK, GLP-1 weight loss injections are prescription-only medicines requiring clinical assessment. You may be eligible if you have a BMI of 30 or above, or a BMI of 27–29.9 with weight-related health conditions (type 2 diabetes, high blood pressure, sleep apnoea, or cardiovascular disease). Lower BMI thresholds (27.5+) apply to adults of South Asian, Chinese, Black African, or Black Caribbean heritage.
Access is available through NHS specialist weight management services (typically tier 3 services via GP referral—availability varies by region) or through private online prescribing from UK-licensed prescribers. A clinical assessment is always required before prescription. Use our free BMI calculator above to check whether your BMI may fall within eligible ranges, and consult your GP or a licensed prescriber about suitability for you personally.
- 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 is the difference between Wegovy and Ozempic?
Both contain semaglutide, but Ozempic is licensed for type 2 diabetes (up to 2 mg dose). Wegovy is the licensed weight management version (up to 2.4 mg). Ozempic is not approved for weight loss in the UK—using it off-label for weight loss is not recommended. Always use the medication prescribed to you.
How much weight can I lose with GLP-1 medication?
Clinical trials show average weight loss of around 15% of body weight, but results vary widely between individuals. Some lose more, some less. Results depend on dose, adherence, diet quality, and exercise. Individual outcomes cannot be assured—a prescriber will discuss realistic expectations with you.
Is GLP-1 weight loss medication available on the NHS?
Yes, GLP-1 medications including Wegovy are approved for NHS use through specialist tier 3 weight management services. However, access varies significantly by region and waiting lists can be lengthy. Private prescribing is also available but involves cost. Ask your GP about NHS options in your area.
What are the common side effects of GLP-1 injections?
Most common: nausea, diarrhoea, vomiting, constipation, and stomach discomfort. Side effects often improve over time as your body adjusts. Serious side effects are rare but can include pancreatitis or gallbladder problems. Always report concerning symptoms to your prescriber immediately.
Can I use a GLP-1 injection if I have type 2 diabetes?
Yes—GLP-1 medications can help both weight management and blood sugar control in type 2 diabetes. However, if you take insulin or other diabetes medications, your doses may need adjustment. Your GP or prescriber will assess your individual situation and monitor you carefully if you start GLP-1 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.