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
Weight Loss Injections in the UK — What You Need to Know
Weight loss injections are prescription-only medicines that may help adults manage their weight when used alongside a reduced-calorie diet and increased physical activity. Also known as "slimming injections" or "weight loss jabs" in the UK, these medications work by regulating appetite and helping you feel fuller after eating. The NHS and private prescribers in the UK offer several licensed options for eligible adults. If you have a BMI of 30 or above, or 27 or above with weight-related health conditions, you may qualify for prescription weight loss medication. Our free GLP-1 weight loss calculator can help you explore potential outcomes, and our BMI calculator lets you check your eligibility category.
10,000+ calculations today · NHS-aligned thresholds · 100% free
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.
UK-Licensed Weight Loss Injections and How They Work
Three prescription weight loss injections are currently licensed in the UK for weight management:
- Mounjaro (tirzepatide) — A dual GIP and GLP-1 receptor agonist given as a once-weekly injection. Clinical trials showed participants lost an average of 15–21% of their body weight over 72 weeks, though individual results vary. Doses range from 2.5 mg to 15 mg weekly.
- Wegovy (semaglutide) — A GLP-1 receptor agonist also given once weekly. STEP clinical trials demonstrated average weight loss of approximately 15% of body weight. Maximum dose is 2.4 mg weekly.
- Saxenda (liraglutide) — A GLP-1 agonist given as a daily injection, with doses from 0.6 mg to 3 mg per day. Less commonly prescribed than Mounjaro or Wegovy in the UK.
All three medications work by affecting hormones that control appetite and blood sugar. They are prescription-only, meaning you cannot buy them over the counter. A licensed prescriber will assess your individual health before prescribing to ensure the medication is suitable and safe for you.
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.
NHS vs Private Access and Eligibility
NHS access: Weight loss medications are available through specialist tier 3 weight management services, typically following GP referral. Eligibility and availability vary significantly by region, and waiting lists can be lengthy in many areas. Your GP can discuss whether you might be suitable for referral.
Private access: You can also obtain a prescription from UK-licensed private prescribers following an online clinical assessment, without needing an NHS referral. Costs vary by medication and dose.
Who is eligible: Adults with a BMI of 30 or above, or 27–29.9 with weight-related health conditions (such as type 2 diabetes, high blood pressure, or cardiovascular disease), may qualify. Lower BMI thresholds apply to adults of South Asian, Chinese, Black African, or Black Caribbean heritage due to higher health risks at lower weights. Use our BMI calculator to check your category, and speak with your GP about your options.
- 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.
How much weight can you lose with weight loss injections?
Clinical trials show average weight loss of 15–21% of body weight with Mounjaro and around 15% with Wegovy, alongside a reduced-calorie diet and increased activity. Individual results vary significantly. Some people lose more, others less. A prescriber can discuss realistic expectations based on your circumstances.
Are weight loss injections available on the NHS in the UK?
Yes, Mounjaro and Wegovy are available through NHS specialist weight management services for eligible adults, but access varies by region and waiting lists can be long. Private access through online prescribers is also available. Your GP can advise on NHS referral options in your area.
What are the side effects of weight loss injections?
Common side effects include nausea, diarrhoea, constipation, stomach pain, and indigestion — especially when starting or increasing doses. Most people find these improve over time. Seek urgent medical attention for severe stomach pain, allergic reactions, or changes in heart rate.
Do I need a prescription for weight loss injections?
Yes, all weight loss injections (Mounjaro, Wegovy, and Saxenda) are prescription-only medicines in the UK. You cannot buy them without a valid prescription from a UK-licensed prescriber, whether through the NHS or a private service.
How do I know if I'm eligible for weight loss injections?
Adults with a BMI of 30 or above, or 27–29.9 with weight-related health conditions, may be eligible. Lower thresholds apply to South Asian, Chinese, Black African, or Black Caribbean adults. Use our free BMI calculator to check your category, then discuss eligibility with your GP or a private 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.