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 Are Weight Loss Injections?
Weight loss injections are prescription-only medications that can support weight management in UK adults. The most widely available options are GLP-1 receptor agonist medications, which work by mimicking a natural hormone that helps regulate appetite and blood sugar. These injections may help you feel fuller after eating smaller meals and reduce food cravings. They're used alongside a reduced-calorie diet and increased physical activity for best results. Individual outcomes vary significantly, and a clinical assessment is required before any prescription is issued.
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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 Weight Loss Injections Work
GLP-1 receptor agonists activate the body's natural GLP-1 hormone pathway, which plays a key role in appetite regulation and blood sugar control. When you take these medications, they signal to your brain that you're satisfied with smaller portions, helping reduce overall calorie intake without feeling deprived.
- Slows gastric emptying — food stays in your stomach longer, keeping you fuller for longer
- Reduces appetite and food cravings
- Helps regulate blood sugar levels
- May improve metabolic function
In clinical trials, GLP-1 medications have shown average weight loss of 14–21% of body weight depending on the specific medication and dose. Try our GLP-1 weight loss calculator to explore potential results at different doses. Weight loss typically becomes noticeable after 4–8 weeks of treatment, though results vary between individuals. These medications require a prescription from a UK-licensed prescriber following a clinical assessment.
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 How to Access Weight Loss Injections
In the UK, prescription weight loss medications may be available if you have a BMI of 30 or above, or a BMI of 27–29.9 with weight-related health conditions such as type 2 diabetes, high blood pressure, or sleep apnoea. Use our BMI calculator to check your personal BMI instantly.
You can access these medications through NHS specialist weight management services (via GP referral to tier 3 services) or through private online prescribing with a UK-licensed prescriber. NHS availability varies by region and may involve waiting lists. Private access is typically faster but involves costs ranging from approximately £129–£320 monthly depending on dose. A prescriber will assess your individual health history and suitability before issuing a prescription.
- 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 assured to work?
No. While clinical trials show average weight loss of 14–21% of body weight, individual results vary significantly. Weight loss depends on the medication, dose, your lifestyle changes, diet, and exercise. A prescriber will discuss realistic expectations during your assessment. Weight loss is not assured.
What's the difference between Wegovy and Ozempic?
Both contain semaglutide, but Wegovy is specifically licensed for weight management in the UK (up to 2.4 mg weekly). Ozempic is approved for type 2 diabetes (up to 2 mg) and is not licensed for weight loss. Using Ozempic for weight loss is off-label. Wegovy is the licensed weight management version.
How long does it take to see weight loss results?
Weight loss typically becomes noticeable after 4–8 weeks of treatment at therapeutic doses. Full results emerge over 12–16 weeks. The medication works gradually, and doses are increased over several weeks. Your prescriber will monitor progress and adjust if needed.
Can I get weight loss injections on the NHS?
Yes, through specialist tier 3 weight management services. You'll need a GP referral. Eligibility is BMI ≥30 or BMI 27–29.9 with weight-related health conditions. NHS availability varies significantly by region and waiting times can be several months. Private access is an alternative.
What are the main side effects of weight loss injections?
Common side effects include nausea, diarrhoea, constipation, and stomach pain—usually mild and temporary. Less common effects include headache, fatigue, and injection site reactions. Serious side effects are rare but can include severe stomach pain (pancreatitis) or gallbladder problems. Always discuss risks with your prescriber.
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.