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 Is Injectable GLP-1 for Weight Management?
Injectable GLP-1 medications are prescription-only treatments that may help with weight management in UK adults. GLP-1 stands for glucagon-like peptide-1, a natural hormone your gut produces after eating. These medications work by mimicking this hormone to help reduce appetite, support feeling fuller after smaller meals, and slow how quickly food leaves your stomach. The most commonly prescribed injectable GLP-1 in the UK for weight loss is Wegovy (semaglutide). These medicines are typically used alongside dietary changes and increased physical activity for best results.
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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 Injectable GLP-1 Medications Work
GLP-1 receptor agonists work by activating natural pathways in your body that regulate appetite and blood sugar. When you eat, your gut naturally releases GLP-1, which tells your brain you're satisfied. Injectable GLP-1 medications amplify this signal, which may help you:
- Feel fuller sooner when eating
- Reduce cravings between meals
- Slow gastric emptying (how quickly food moves through your digestive system)
- Support better blood sugar control
These are not insulin injections — they work through a completely different mechanism. Clinical trials have shown that people using injectable GLP-1 medications alongside a reduced-calorie diet and increased physical activity may achieve weight loss of around 15% of body weight on average, though individual results vary significantly. Your response to the medication will depend on your personal health, lifestyle, and consistency with diet and exercise.
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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.
Eligibility and Access in the UK
To be eligible for injectable GLP-1 medications in the UK, you typically need a BMI of 30 kg/m² or above, or a BMI of 27–29.9 kg/m² if you have at least one weight-related health condition such as type 2 diabetes, prediabetes, high blood pressure, or cardiovascular disease. You can calculate your personal BMI using our free BMI calculator above.
Access in the UK is available through two routes: NHS specialist weight management services (tier 3/4), which require a GP referral and may have waiting lists; or private online prescribing through GPhC-registered pharmacies, which is available without NHS referral. A licensed prescriber must assess you before any prescription is issued — they'll review your medical history and current medications to ensure the treatment is safe and appropriate for you.
- 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.
Is Wegovy the only injectable GLP-1 available in the UK?
Wegovy (semaglutide) is the most commonly prescribed injectable GLP-1 for weight management in the UK. Saxenda (liraglutide) is also licensed — it's a once-daily injection rather than once-weekly. Mounjaro (tirzepatide) is technically a dual GIP and GLP-1 agonist, not a single GLP-1, but works similarly. All three are prescription-only and require clinical assessment.
What's the difference between Wegovy and Ozempic if they both contain semaglutide?
Both Wegovy and Ozempic contain semaglutide, but they're different medicines for different purposes. Ozempic is licensed for type 2 diabetes and contains doses up to 2 mg. Wegovy is licensed specifically for weight management and contains doses up to 2.4 mg. Using Ozempic for weight loss is off-label; Wegovy is the licensed weight management version.
How long do you stay on injectable GLP-1 medication?
Duration depends on individual circumstances and prescriber guidance. Some people use it for a defined period (e.g., 12 months), while others continue longer-term. If you stop, weight may return gradually — these medications support weight loss alongside lifestyle changes rather than providing permanent results. Discuss your plan with your prescriber.
Can I get injectable GLP-1 through the NHS in my area?
NHS availability varies significantly by region and ICB (Integrated Care Board). Some areas have good access to specialist weight management services; others have long waiting lists or limited provision. Contact your GP to ask about referral to your local tier 3 weight management service, or ask about private options if NHS access is limited.
What side effects might I experience with injectable GLP-1?
Common side effects include nausea, diarrhoea, vomiting, and stomach pain — these often improve as your body adjusts. Less common side effects include constipation, headache, fatigue, and injection site reactions. Serious side effects are rare but can include severe stomach pain (possible pancreatitis) or gallbladder issues. Always discuss side effects with your prescriber and report any concerning symptoms promptly.
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.