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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Fat Injections for Weight Loss — UK Options Explained
Fat injections, also called slimming injections or weight loss jabs, are prescription-only medications licensed in the UK to help adults manage excess weight. These medications are not cosmetic injectables — they are clinically tested treatments that work by affecting appetite and how your body processes food. The UK currently has three licensed options available, each with different mechanisms and dosing schedules. This guide explains how they work, compares your choices, and covers how to access them through both NHS and private routes.
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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 Weight Loss Injection Options
Three GLP-1 (and GIP/GLP-1) medications are currently licensed in the UK for weight loss injections and are the main options available:
- Mounjaro (tirzepatide) — A dual GIP and GLP-1 receptor agonist given as a once-weekly injection. Starting dose 2.5 mg, escalating to a maximum of 15 mg weekly. Clinical trials showed average weight loss of approximately 15–21% of body weight over 72 weeks alongside diet and exercise changes.
- Wegovy (semaglutide) — A GLP-1 receptor agonist given as a once-weekly injection. Doses range from 0.25 mg to 2.4 mg. The STEP trials demonstrated average weight loss of around 15% of body weight at the maximum dose.
- Saxenda (liraglutide) — A GLP-1 receptor agonist administered as a daily injection (not weekly). Maximum dose 3 mg daily. This option has a longer track record and is often available sooner on the NHS in some regions.
All three are prescription-only medicines requiring clinical assessment before dispensing. The choice between them depends on individual health factors, preference for injection frequency, and availability through your chosen access route (NHS or private).
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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.
Accessing Weight Loss Injections — NHS vs Private
NHS access: Weight loss injections are available through specialist tier 3 and tier 4 weight management services. Your GP can refer you if you meet eligibility criteria — typically a BMI of 30 or above, or 27 or above with weight-related health conditions such as type 2 diabetes, high blood pressure, or cardiovascular disease. Waiting times vary significantly by region; some areas have waiting lists of several months or longer.
Private access: All three medications are available through private online consultations with UK-licensed prescribers. Following an online clinical assessment, a prescription is issued and dispensed by a GPhC-registered pharmacy. This route typically has no waiting list but involves upfront costs. Doses are priced individually; costs generally range from £129 to £320 monthly depending on dose level.
Whichever route you choose, these are always prescription-only treatments requiring proper medical assessment — they cannot be purchased without a valid prescription.
- 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 fat injections and other weight loss treatments?
Fat injections (slimming injections) are prescription medications that work by affecting hormones that control appetite and food processing. They differ from cosmetic fat-dissolving injections, which are non-prescription aesthetic procedures. Unlike oral weight loss medications or surgery, injections activate natural hormone pathways. All UK-licensed options require a prescription and clinical assessment.
How quickly do fat injections work?
Weight loss typically becomes noticeable after 2–4 weeks, with more significant results visible after 8–12 weeks. Clinical trials measured results over 68–72 weeks. The rate of weight loss varies between individuals and depends on dose, diet, and exercise changes. Use our GLP-1 weight loss calculator to see projected results at different doses.
Are fat injections available on the NHS?
Yes, but access is through specialist weight management services, not standard GP prescription. You need a GP referral and must meet eligibility criteria (BMI 30+, or 27+ with weight-related conditions). Availability and waiting times vary greatly by region. Private access through online prescribing is available without NHS referral.
What are the main side effects of slimming injections?
The most common side effects are nausea, diarrhoea, constipation, and stomach pain — usually mild and improving over time as the body adjusts. Serious side effects are rare but can include pancreatitis (severe stomach pain). All medications have detailed patient information leaflets. Your prescriber will discuss risks specific to your health before starting treatment.
Can I check my current weight status before considering fat injections?
Yes. Use our free BMI calculator to check your current BMI against NHS healthy weight ranges. You can also use the weight converter to see your weight in stone, lbs, or kg. Knowing your BMI and current measurements helps you discuss options with your GP or 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.