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
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GLP-1 Medications for Weight Loss in the UK
GLP-1 medications are prescription-only weight loss treatments available in the UK that work by mimicking a natural gut hormone to help reduce appetite and support weight management. These medications have become increasingly popular options for adults struggling with excess weight, particularly those with a BMI of 30 or above, or 27–29.9 with weight-related health conditions. This guide explains how GLP-1 medications work, what UK options are available, and what evidence shows about their effectiveness.
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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 stands for glucagon-like peptide-1, a natural hormone your gut produces after eating. It signals to your brain that you are full, slows how quickly food leaves your stomach, and helps regulate blood sugar levels. GLP-1 medications are receptor agonists — they mimic and amplify these effects.
In clinical trials, adults taking GLP-1 medications alongside a reduced-calorie diet and increased physical activity lost significantly more weight than those on diet and exercise alone. For example, the STEP trials showed that Wegovy (semaglutide) helped participants lose an average of approximately 15% of their body weight over 68 weeks at the maximum dose — though individual results vary considerably.
- May help reduce appetite and food cravings
- Supports feeling fuller after smaller meals
- Slows gastric emptying (digestion)
- Does not work like insulin — it is a different medication class entirely
Try our free GLP-1 weight loss calculator to estimate potential weight loss outcomes at different dose levels based on clinical trial data.
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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.
GLP-1 Medications Available in the UK
Three GLP-1 medications are currently licensed for weight management in the UK:
- Wegovy (semaglutide) — once-weekly injection, doses 0.25mg to 2.4mg
- Saxenda (liraglutide) — once-daily injection, doses 0.6mg to 3mg
- Mounjaro (tirzepatide) — once-weekly injection, doses 2.5mg to 15mg (technically a dual GIP+GLP-1 agonist)
All three are prescription-only medicines requiring clinical assessment before use. You can access them through NHS specialist weight management services or private prescribing following an online consultation with a UK-licensed prescriber. Check your BMI using our free BMI calculator to see if you meet the eligibility criteria.
Access varies significantly depending on your chosen route. NHS access requires referral to a tier 3 specialist weight management service, which can involve substantial waiting lists in many regions. Private online prescribing offers faster access without NHS referral, though costs apply. A prescriber will assess your individual health circumstances, weight loss goals, and suitability before issuing a prescription — medication is not suitable for everyone.
All GLP-1 medications work best when combined with lifestyle changes including a reduced-calorie diet and regular physical activity. Weight loss results vary between individuals based on genetics, adherence to treatment, diet quality, and exercise level. Many people continue medication for long-term weight maintenance once target weight is reached.
- 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 (doses up to 2mg). Wegovy is the licensed weight management version (up to 2.4mg). Ozempic is not licensed for weight loss in the UK — using it for weight loss would be off-label. Always use the medication licensed for your specific condition.
How quickly will I lose weight on GLP-1 medication?
NHS recommends sustainable weight loss of 0.5–1kg per week. Clinical trials showed participants lost an average of 15–21% of body weight over 68 weeks, though results vary significantly. Weight loss is not assured — it depends on adherence to medication, diet quality, physical activity, and individual metabolism.
Do GLP-1 medications have side effects?
Yes. Very common side effects include nausea, diarrhoea, vomiting, and constipation — often mild and temporary. Less common but serious side effects can include severe stomach pain (possible pancreatitis) and gallbladder problems. Always report new or worsening symptoms to your prescriber immediately.
Can I stop taking GLP-1 medication once I reach my target weight?
Yes. Many people continue medication long-term for weight maintenance after reaching their goal, though some stop and maintain through lifestyle alone. Your prescriber can advise on the best approach for you. Stopping suddenly may result in weight regain — any changes should be discussed with your healthcare provider.
How do I know if I'm eligible for GLP-1 weight loss medication?
Generally, adults with a BMI of 30 or above, or 27–29.9 with weight-related conditions (type 2 diabetes, high blood pressure, high cholesterol), may be eligible. South Asian, Chinese, Black African, and Black Caribbean adults have lower eligibility thresholds. A GP or prescriber will assess your individual circumstances — use our BMI calculator to check your starting point.
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.