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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Slimming Injections Names — UK Licensed Weight Loss Options
Slimming injections, also called weight loss injections or fat jabs, are prescription-only medicines used to support weight management in UK adults. There are currently three main licensed options available: Mounjaro, Wegovy, and Saxenda. All work by mimicking natural hormones that regulate appetite and food intake. Each has a different mechanism, injection frequency, and dose range. Understanding the names, how each one works, and how to access them through the NHS or privately can help you make an informed decision with your GP or prescriber.
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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.
UK-Licensed Slimming Injections — Mounjaro, Wegovy, and Saxenda Compared
The three prescription slimming injections licensed for weight management in the UK are:
- Mounjaro (tirzepatide) — A dual GIP and GLP-1 receptor agonist made by Eli Lilly. Injected once weekly. Available doses range from 2.5 mg to 15 mg. Clinical trials showed an average weight loss of 15–21% of body weight over 72 weeks, though individual results vary significantly.
- Wegovy (semaglutide) — A GLP-1 receptor agonist made by Novo Nordisk. Injected once weekly. Available doses range from 0.25 mg to 2.4 mg. Clinical trial data showed average weight loss of approximately 15% of body weight, achieved alongside a reduced-calorie diet and increased physical activity.
- Saxenda (liraglutide) — A GLP-1 receptor agonist made by Novo Nordisk. Daily injection required (not weekly). Doses range from 0.6 mg to 3 mg. Average weight loss is typically 5–10% of body weight.
All three are prescription-only medicines requiring a clinical assessment before prescribing. The choice between them depends on individual health factors, medical history, and prescriber recommendation.
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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.
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How to Access Slimming Injections in the UK — NHS and Private Routes
NHS access: Weight loss injections (including Mounjaro and Wegovy) are available through NHS specialist tier 3 or tier 4 weight management services. You will need a referral from your GP and must meet specific BMI and health criteria. Regional availability varies significantly — some areas have lengthy waiting lists. Private access: You can obtain a prescription for weight loss injections uk through a private online consultation with a UK-licensed prescriber (GP or clinical pharmacist). Following a clinical assessment, a prescription is issued and dispensed by a GPhC-registered pharmacy. No NHS referral is required. Costs vary by medication, dose, and provider. All slimming injections are prescription-only and require an individual assessment of eligibility.
- 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 slimming injections called anything else in the UK?
Yes, they are commonly called weight loss injections, fat jabs, slimming jabs, or weight loss jabs. These colloquial terms all refer to the same prescription medications — GLP-1 and GIP receptor agonists. The medical names are Mounjaro, Wegovy, and Saxenda. They are not the same as cosmetic fat-dissolving injections.
What is the difference between Mounjaro and Wegovy?
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist, while Wegovy (semaglutide) is a GLP-1 agonist only. Mounjaro may have a slightly stronger effect on appetite regulation due to its dual mechanism. Both are once-weekly injections. Clinical trial data suggests similar average weight loss (15–21% with Mounjaro, approximately 15% with Wegovy), though individual results vary. Your prescriber will assess which is more suitable for you.
Can I get slimming injections on the NHS?
Yes, prescription slimming injections are available on the NHS through specialist weight management services. However, access varies significantly by region and availability may be limited. You need a GP referral and must meet specific BMI and health criteria. Many areas have long waiting lists. Private access is faster but involves cost. Ask your GP about availability in your area.
How do I know which slimming injection is right for me?
Only a qualified prescriber (GP, nurse, or clinical pharmacist) can assess which weight loss injection is suitable based on your health history, current medications, BMI, and medical conditions. You cannot choose between them yourself. Your prescriber will recommend the most appropriate option. Try our free BMI calculator above to check where you currently stand, then discuss prescription options with your GP or healthcare provider.
Are slimming injections safe?
All three UK-licensed slimming injections have undergone rigorous safety testing and regulatory approval by the MHRA. Common side effects include nausea, diarrhoea, and constipation, which often improve with time. Serious side effects are rare but can occur — your prescriber will discuss these with you before prescribing. They are not suitable for everyone (for example, people who are pregnant or have a personal or family history of thyroid cancer). Always discuss safety concerns with your healthcare provider.
Ready to take control of your weight loss journey?
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