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
Injections to Lose Weight — What You Need to Know
Weight loss injections are prescription-only medicines that may help with sustainable weight loss when combined with diet and exercise. In the UK, two main GLP-1 injections are licensed for weight management: Wegovy (semaglutide) and Mounjaro (tirzepatide). These medications work by mimicking natural hormones that regulate appetite and help you feel fuller after smaller meals. Access is available through NHS weight management services or private online prescribing following a clinical assessment. This guide explains how they work, who may be eligible, and what to expect.
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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 Weight Loss Injections Work
Weight loss injections available in the UK are GLP-1 receptor agonists or dual GIP/GLP-1 agonists — medications that activate natural hormone pathways controlling appetite and food intake.
Wegovy (semaglutide) activates the GLP-1 pathway, signalling to your brain that you are full and helping reduce cravings. Clinical trials showed participants lost an average of 15% of their body weight over 68 weeks, though individual results vary significantly.
Mounjaro (tirzepatide) is a dual agonist, activating both GIP and GLP-1 pathways. SURMOUNT trials demonstrated average weight loss of 15–21% body weight depending on dose.
Both medications slow how quickly food leaves your stomach, work alongside a reduced-calorie diet, and require commitment to lifestyle changes. Weight loss is not assured — results depend on individual factors including adherence, diet, and physical activity. Use our free GLP-1 weight loss calculator above to estimate potential results at different doses based on your current weight.
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
You may be eligible for prescription weight loss injections in the UK if you have:
- A BMI of 30 or above, OR
- A BMI of 27–29.9 with a weight-related health condition (type 2 diabetes, prediabetes, high blood pressure, or cardiovascular disease)
For people of South Asian, Chinese, Black African, or Black Caribbean heritage, lower BMI thresholds apply.
NHS access: Referral to a tier 3 specialist weight management service through your GP. Availability varies by region; waiting lists can be lengthy. Private access: Online consultation with a UK-licensed prescriber, prescription issued if clinically appropriate, dispensed by a GPhC-registered pharmacy. Check your BMI using our free BMI calculator to see if you may qualify for treatment. A prescriber will assess your full medical history before prescribing.
- 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?
GLP-1 medications are licensed and regulated in the UK. Common side effects include nausea, constipation, and stomach pain — usually mild and temporary. Serious side effects are rare but include pancreatitis and gallbladder problems. Your prescriber will assess whether the medication is safe for you based on your medical history. Always report unusual symptoms to your GP.
How much weight will I lose with weight loss injections?
Clinical trials show average weight loss of 15–21% of body weight over several months, though individual results vary significantly. Some people lose more, some less. Weight loss depends on dose, adherence to the medication, calorie intake, physical activity, and individual metabolism. Our GLP-1 calculator can give you a personalised estimate based on your starting weight.
Is Ozempic the same as weight loss injections?
No. Ozempic contains semaglutide but is licensed for type 2 diabetes, not weight loss in the UK. Wegovy is the licensed weight management version of semaglutide. Using Ozempic for weight loss is off-label. Always ensure your prescription specifically states Wegovy if that is the medication you need.
Can I get weight loss injections on the NHS?
Yes, through NHS tier 3 specialist weight management services. Your GP can refer you, but you must meet eligibility criteria (BMI 30+ or 27+ with comorbidities) and be assessed by a specialist team. Availability varies significantly by region, and waiting lists can be several months to over a year depending on your area.
Do weight loss injections work without diet and exercise changes?
No. Weight loss injections are most effective alongside reduced-calorie diet and increased physical activity. They are a tool to support lifestyle changes, not a replacement for them. The medication may help reduce appetite, making diet changes easier, but sustainable weight loss requires commitment to healthier habits.
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.