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 Fat Injection Weight Loss Treatments?
Fat injection weight loss treatments—commonly called slimming injections or weight loss jabs in the UK—are prescription-only medicines that help reduce appetite and support weight management. They're not cosmetic injections; they're licensed medications that work by mimicking natural hormones your body produces after eating. Three options are currently available through the NHS or private prescription in the UK: Mounjaro, Wegovy, and Saxenda. Each uses different mechanisms to help you feel fuller for longer and eat less, alongside a reduced-calorie diet and increased physical activity. Understanding what these injections actually do—and aren't—is essential before considering whether they're right for you.
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.
Three UK-Licensed Weight Loss Injections
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist—the newest option for weight loss in the UK. It's a once-weekly injection that activates two natural hormone pathways to regulate appetite and reduce cravings. In clinical trials, adults lost an average of 15–21% of their body weight, though individual results vary significantly.
Wegovy (semaglutide) is a GLP-1 receptor agonist—a single-mechanism injection also given once weekly. Clinical trials showed average weight loss of around 15% of body weight over 68 weeks. Wegovy has been available for weight management in the UK for longer than Mounjaro.
Saxenda (liraglutide) is also a GLP-1 receptor agonist but is given as a daily injection rather than weekly. It's been licensed for weight management in the UK since 2015. All three are prescription-only medicines requiring clinical assessment before being prescribed.
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.
How Slimming Injections Work—The GLP-1 Mechanism
GLP-1 weight loss injections work by mimicking a natural hormone your gut produces after eating. This hormone tells your brain you're full, slows how quickly food leaves your stomach, and helps regulate blood sugar. By amplifying this signal, these injections help you eat less without feeling hungry, making it easier to maintain a calorie deficit. Results depend on combining the injection with dietary changes and physical activity—the medication supports your efforts, it doesn't replace them. Try our free GLP-1 weight loss calculator to see projected weight loss estimates at different doses, and use our BMI calculator to understand your current health category and set realistic goals.
- 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 fat injection weight loss treatments the same as cosmetic fat-dissolving injections?
No. Weight loss injections like Mounjaro and Wegovy are prescription-only medicines that work internally by regulating appetite hormones. Cosmetic fat-dissolving injections (like aqualyx) are different products used for localised fat reduction. Weight loss injections are medical treatments requiring clinical assessment; cosmetic injections are elective aesthetic procedures.
How do I get a weight loss injection on the NHS in the UK?
NHS access is through specialist tier 3 weight management services. Your GP can refer you if you meet eligibility criteria (BMI 30+ or 27+ with weight-related health conditions). NHS availability varies by region and waiting lists can be lengthy. Private prescription is available through online clinical assessments with UK-licensed prescribers.
What's the difference between Mounjaro, Wegovy, and Saxenda?
All three are GLP-1 medications but work slightly differently. Mounjaro (tirzepatide) is dual-action GIP+GLP-1. Wegovy and Saxenda are GLP-1-only. Mounjaro and Wegovy are weekly injections; Saxenda is daily. Clinical trials show similar average weight loss (15–21%), but individual responses vary. Your prescriber will assess which is most suitable for you.
Are weight loss injections assured to work?
No. Clinical trials show average weight loss of 15–21%, but individual results vary significantly. Some people lose more, some less. These medications work best alongside a reduced-calorie diet and increased physical activity. They support your weight loss efforts but don't replace lifestyle changes.
What are the main side effects of weight loss injections?
Common side effects include nausea, diarrhoea, constipation, and stomach pain—especially when starting or increasing doses. These usually improve over time. Serious side effects are rare but can include pancreatitis or gallbladder problems. Your prescriber will discuss all risks during your clinical assessment.
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.