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
Weight Loss Injections — UK Options Explained
Fat injections for weight loss, commonly known as slimming injections or weight loss jabs in the UK, are prescription-only medications that may help support weight management when combined with lifestyle changes. Three main medications are currently licensed in the UK: Mounjaro (tirzepatide), Wegovy (semaglutide), and Saxenda (liraglutide). Each works through different mechanisms and dosing schedules. Understanding your options—including eligibility, NHS access, and private routes—is essential before discussing prescription slimming injections with your GP or a healthcare professional. Use our free GLP-1 weight loss calculator above to explore potential outcomes, and our BMI calculator to understand your current weight category.
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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.
UK Weight Loss Injections — How They Compare
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist—meaning it activates two natural hormone pathways to help reduce appetite and support feeling fuller after meals. It's administered once weekly via pre-filled pen, starting at 2.5 mg and escalating up to 15 mg. Clinical trials showed average weight loss of approximately 15–21% of body weight over 72 weeks, though individual results vary significantly.
Wegovy (semaglutide) is a GLP-1 receptor agonist—activating a single hormone pathway. Also injected once weekly, it starts at 0.25 mg and reaches a maximum of 2.4 mg. STEP trial data showed average weight loss of around 15% body weight, alongside reduced-calorie diet and increased physical activity.
Saxenda (liraglutide) is also a GLP-1 agonist but differs in frequency—it's a once-daily injection rather than weekly. It escalates from 0.6 mg to 3 mg daily. All three require a prescription and clinical assessment before use. Weight loss injections work best alongside lifestyle changes, not as standalone treatments.
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.
NHS Access vs Private Routes — Eligibility and How to Get Started
In the UK, prescription weight loss injections are available through two routes. NHS access is through specialist tier 3/4 weight management services—you'll need a GP referral, and availability varies significantly by region. NHS waiting lists can extend months or years in many areas. Private access is available through GPhC-registered online pharmacies following a clinical assessment with a UK-licensed prescriber—no NHS referral required.
Eligibility for both routes: Adults with a BMI of 30 or above, or 27–29.9 with at least one weight-related health condition (type 2 diabetes, high blood pressure, cardiovascular disease, sleep apnoea, or abnormal blood fats). For South Asian, Chinese, Black African, or Black Caribbean adults, lower BMI thresholds may apply. A prescriber will assess whether prescription weight loss treatment is suitable for your individual health. Track your progress with our free progress tracker once you begin your weight loss journey.
- 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 GLP-1 weight loss injections and fat-dissolving injections?
GLP-1 weight loss injections (like Wegovy and Mounjaro) are prescription medications that work on hormone pathways to reduce appetite. Fat-dissolving injections (like Aqualyx) are cosmetic treatments that chemically dissolve localised fat deposits. They're entirely different: GLP-1 injections are for systemic weight management and require clinical assessment; fat-dissolving injections are non-prescription cosmetic procedures with different risks and benefits.
Can I get weight loss injections on the NHS?
Yes, but access is limited. Weight loss injections are prescribed through NHS specialist weight management services (tier 3/4), typically requiring a GP referral. Availability and waiting times vary significantly by region—some areas have long waits or limited capacity. Private routes through GPhC-registered pharmacies offer faster access following an online clinical assessment.
Which weight loss injection is most effective?
Individual results vary significantly, and "most effective" depends on your personal response. Mounjaro showed slightly higher average weight loss (15–21%) than Wegovy (around 15%) in clinical trials, but differences are modest and individual outcomes differ. Your GP or prescriber will recommend the most suitable option based on your health profile, not assumed superiority.
Are there side effects with weight loss injections?
Yes. Common side effects include nausea, diarrhoea, constipation, and stomach pain—especially when starting or increasing doses. Most subside over time. Serious but rare side effects include pancreatitis or gallbladder problems. Always discuss potential side effects with your prescriber before starting, and report any severe or persistent symptoms immediately.
Do I need to take weight loss injections forever?
No. Weight loss injections are typically used for a defined period—often 12–24 months—to support weight loss alongside lifestyle changes. After stopping, maintaining weight loss depends on sustaining the diet and exercise habits you've developed. Some people may restart treatment if weight returns; others maintain without medication. Your prescriber will discuss the right duration for your situation.
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.