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
Do Fat Loss Injections Work — What You Need to Know
Fat loss injections—commonly called slimming injections or weight loss jabs in the UK—are prescription-only medicines that help regulate appetite and support weight management. Clinical evidence shows they can be effective when combined with lifestyle changes, though individual results vary significantly. This guide explains how they work, which options are available in the UK, and whether they might be suitable for you.
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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.
Three UK-Licensed Fat Loss Injection Options
Three prescription slimming injections are currently licensed for weight management in the UK:
- Mounjaro (tirzepatide)—a dual GIP and GLP-1 receptor agonist. Clinical trials showed participants lost an average of 15–21% of their body weight over 72 weeks. Doses range from 2.5 mg to 15 mg once weekly.
- Wegovy (semaglutide)—a GLP-1 receptor agonist. STEP trial data showed approximately 14.9% average body weight loss at the maximum 2.4 mg dose. Administered once weekly.
- Saxenda (liraglutide)—also a GLP-1 agonist, but given as a once-daily injection rather than weekly. Maximum dose is 3 mg daily.
All three require a clinical assessment and prescription from a UK-licensed prescriber. Access through the NHS is via specialist tier 3 weight management services, though private prescribing is also available through registered online services.
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 Weight Loss Injections Actually Work
GLP-1 weight loss injections mimic a natural hormone (glucagon-like peptide-1) produced in your gut. This hormone signals fullness to your brain, helping you feel satisfied after smaller meals and reducing cravings. The injections slow how quickly food leaves your stomach, regulate blood sugar, and may help your body use fat more efficiently. Mounjaro adds an extra mechanism by also activating the GIP pathway, which may explain slightly higher average weight loss in trials.
Results depend on multiple factors: your starting weight, adherence to reduced-calorie diet and physical activity, dose reached, and individual metabolism. Even modest weight loss—as little as 5–10% of body weight—can improve blood pressure, blood sugar control, and reduce joint stress.
- 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 loss injections the same as cosmetic injections?
No. Slimming injections are prescription-only medicines (not cosmetic treatments) that work systemically to regulate appetite hormones. They are different from cosmetic fat-dissolving injections. All weight loss injections available on the NHS are licensed medications requiring clinical assessment.
How quickly will I see results from weight loss injections?
Most people notice changes within 2–4 weeks of starting, though significant weight loss typically becomes apparent over 8–12 weeks. Clinical trials measured results over 68–72 weeks. Weight loss continues as your dose is increased, but results vary individually.
Can I get fat loss injections on the NHS?
Yes, through specialist tier 3 weight management services. Your GP can refer you, though waiting times vary significantly by region. Private prescribing through registered online services is also available without an NHS referral, though this involves a cost.
Do weight loss injections work without diet and exercise?
Clinical trials show weight loss injections are most effective alongside a reduced-calorie diet and increased physical activity. They support and enhance these lifestyle changes but are not a replacement for them. Your prescriber will discuss lifestyle alongside medication.
What happens when you stop taking weight loss injections?
Weight regain can occur after stopping, though some people maintain weight loss through sustained lifestyle changes. Your prescriber will discuss long-term management plans, including whether ongoing treatment is appropriate for you.
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.