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
Slimming Jabs in the UK — Your Complete Options Guide
Slimming jabs, also known as weight loss injections or fat jabs UK, are prescription-only medications that help support weight management in adults. Three licensed options are available in the UK: Mounjaro (tirzepatide), Wegovy (semaglutide), and Saxenda (liraglutide). All work by mimicking natural hormones that regulate appetite and blood sugar. Access is available through the NHS for eligible patients or privately through UK-licensed prescribers. This guide explains how each medication works, the differences between them, and how to access them.
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.
How the Three UK-Licensed Slimming Jabs Work
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist — it activates two natural hormone pathways to help reduce appetite and support feeling fuller after eating. Given as a once-weekly injection, doses range from 2.5 mg to 15 mg. Clinical trials showed average weight loss of around 15–21% of body weight alongside a reduced-calorie diet and increased physical activity.
Wegovy (semaglutide) is a GLP-1 receptor agonist — a single-hormone approach. Also injected once weekly, doses escalate from 0.25 mg to a maximum of 2.4 mg. Clinical evidence showed average weight loss of approximately 15% of body weight in trials.
Saxenda (liraglutide) is also a GLP-1 receptor agonist but administered as a daily injection rather than weekly. It reaches a maximum dose of 3 mg per day. All three are prescription-only medicines requiring clinical assessment before being prescribed.
- Mounjaro: once weekly, doses up to 15 mg
- Wegovy: once weekly, doses up to 2.4 mg
- Saxenda: once daily, doses up to 3 mg
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.
Accessing Slimming Injections — NHS vs Private Routes
NHS access is available through specialist tier 3 weight management services. Your GP can refer you to the local NHS weight management team if you meet eligibility criteria: 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. For people of South Asian, Chinese, Black African, or Black Caribbean heritage, lower BMI thresholds may apply. NHS availability varies significantly by region, and waiting lists can be several months in many areas.
Private access is available without NHS referral through GPhC-registered online pharmacies. A UK-licensed prescriber will assess your medical history and eligibility following an online consultation. Prescription slimming injections are dispensed by registered pharmacies. All three medications are prescription-only in the UK — none are available over-the-counter. Try our GLP-1 weight loss calculator to explore potential results, and use the BMI calculator to check your current eligibility status.
- 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 Mounjaro, Wegovy, and Saxenda?
Mounjaro (tirzepatide) works on two hormone pathways (GIP and GLP-1) and is given once weekly. Wegovy (semaglutide) targets one pathway (GLP-1) and is also once weekly but at lower doses. Saxenda (liraglutide) is a daily injection, not weekly. All are prescription-only and may help reduce appetite and support weight loss alongside lifestyle changes.
Are slimming jabs safe?
All three medications are UK-licensed and have undergone rigorous clinical testing. Common side effects include nausea, diarrhoea, and constipation — typically mild and short-lived. Serious side effects are rare but possible; discuss any concerns with your prescriber or GP before starting treatment.
Can I access slimming jabs through the NHS?
Yes, if you meet eligibility criteria (BMI ≥30 or ≥27 with weight-related health conditions) and are referred to a specialist NHS weight management service by your GP. Availability varies by region. Private access via online prescribers is also available without NHS referral.
How much weight can I expect to lose?
Clinical trials show average weight loss of 15–21% of body weight, but individual results vary significantly. Some people lose more, others less. Results depend on adherence to medication, diet, exercise, and individual metabolism. Always discuss realistic expectations with your prescriber.
Are prescription slimming injections available without a prescription?
No. Mounjaro, Wegovy, and Saxenda are all prescription-only medicines in the UK. You must have a prescription from a UK-licensed prescriber (either NHS or private). They cannot be purchased over-the-counter or without a 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.