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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Injection Shots For Weight Loss — What You Need To Know
Injection shots for weight loss are prescription-only medicines that may help you lose weight when used alongside diet and exercise. In the UK, the main weight management injections available are GLP-1 receptor agonists like Wegovy (semaglutide) and Mounjaro (tirzepatide). These medications work by reducing appetite and helping you feel fuller after eating. They're available through the NHS specialist weight loss services or private prescribing pathways. Understanding how they work and whether you're eligible is the first step toward considering weight management with medication.
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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 Weight Loss Injection Shots Work
Weight loss injection shots fall into two categories in the UK: GLP-1 receptor agonists (like Wegovy) and GIP/GLP-1 receptor agonists (like Mounjaro). Both work by mimicking natural hormones produced in your gut.
- Wegovy (semaglutide): A GLP-1 injection given once weekly. Clinical trials showed it helped participants lose an average of 15% of their body weight over 68 weeks, though individual results vary significantly.
- Mounjaro (tirzepatide): A newer dual-action injection that activates two hormone pathways (GIP and GLP-1). In clinical trials, it showed average weight loss of 15–21% of body weight, with individual results varying.
Both medications work by reducing your appetite, helping you feel satisfied with smaller portions, and slowing how quickly food leaves your stomach. They're not insulin and don't work the same way as diabetes medications. Weight loss injections are part of a weight management programme — they're most effective when combined with a reduced-calorie diet and increased physical activity.
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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
To access weight loss injection shots in the UK, you'll need to meet specific NHS weight loss criteria or go through private prescribing. Eligibility generally includes:
- BMI of 30 kg/m² or above, or BMI 27–29.9 with weight-related health conditions (such as type 2 diabetes, high blood pressure, or sleep apnoea)
- Lower BMI thresholds apply if you're of South Asian, Chinese, Black African, or Black Caribbean heritage
- Age 18 or over
- Not pregnant or breastfeeding
You can access weight loss injections through the NHS specialist tier 3 weight management services (referral required from your GP), or privately through an online consultation with a UK-licensed prescriber. Private access is typically faster but involves a cost. Use our free BMI calculator to check your starting point, and then discuss options with your GP or a licensed prescriber who can assess your suitability.
- 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's the difference between weight loss injection shots available in the UK?
Wegovy (semaglutide) is a once-weekly GLP-1 injection with average weight loss of ~15% body weight. Mounjaro (tirzepatide) is also once-weekly but uses dual GIP/GLP-1 action, showing average loss of 15–21%. Both require prescription. Results vary individually. Your prescriber will advise which suits you.
How quickly will I lose weight with injection shots?
Weight loss is gradual and varies by person. The NHS recommends losing 0.5–1 kg per week for sustainable results. Clinical trials show meaningful weight loss within 4–8 weeks, with maximum effect typically seen after 16–20 weeks. Injections work best alongside diet and exercise changes.
Can I get weight loss injection shots on the NHS?
Yes. NHS specialist tier 3 weight management services can prescribe weight loss injections if you meet eligibility criteria. However, availability varies significantly by region and waiting lists can be lengthy. Your GP can refer you. Private prescription is faster but costs approximately £129–£320+ per month depending on dose.
Are weight loss injection shots safe?
Prescription weight loss injections are licensed and undergo strict safety monitoring. Common side effects include nausea, diarrhoea, and constipation, which often improve over time. Serious side effects are rare but include severe stomach pain or allergic reactions. Always discuss risks with your prescriber before starting.
What happens if I stop using weight loss injection shots?
Weight loss may slow or plateau if you stop injections without maintaining diet and exercise changes. Some people regain weight gradually after stopping. Injections are typically part of a longer-term weight management approach, not a structured approach. Discuss duration and stopping plans 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.