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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The Best Weight Loss Injections Available in the UK
If you're considering weight loss injections, you're looking at prescription-only medications that may help support weight management alongside lifestyle changes. In the UK, three main weight loss injections are currently licensed: Wegovy (semaglutide), Mounjaro (tirzepatide), and Saxenda (liraglutide). Each works through different mechanisms and offers different benefits. This guide explains how they work, who's eligible, and what the evidence shows about their effectiveness. Always remember that individual results vary significantly, and any weight loss injection requires a prescription following clinical assessment by a healthcare professional.
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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.
How Weight Loss Injections Work
Weight loss injections licensed for weight management in the UK are mostly GLP-1 receptor agonists—medications that mimic a natural gut hormone. Wegovy (semaglutide) activates GLP-1 pathways to reduce appetite and help you feel fuller after smaller meals. Mounjaro (tirzepatide) is unique because it's a dual GIP and GLP-1 agonist, activating two hormone pathways for potentially stronger appetite suppression. Saxenda (liraglutide) is a once-daily GLP-1 injection, whereas Wegovy and Mounjaro are once-weekly.
In clinical trials, Wegovy helped participants lose an average of 14.9% of body weight over 68 weeks, while Mounjaro showed average losses of 15–21% depending on dose. These results were achieved alongside a reduced-calorie diet and increased physical activity. All three medications slow how quickly food leaves your stomach and signal to your brain that you're satisfied, which helps reduce food cravings and support sustainable eating habits.
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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.
Free Weight Loss Tools & Guides
Everything you need to understand your weight, explore medication options, and track your progress — completely free.
Eligibility and Access in the UK
Prescription weight loss medications in the UK are available to adults who meet specific criteria. You're typically eligible if you have a BMI of 30 or above, or a BMI of 27–29.9 with weight-related health conditions such as type 2 diabetes, prediabetes, high blood pressure, or cardiovascular disease. For South Asian, Chinese, Black African, or Black Caribbean adults, lower BMI thresholds apply due to higher health risks at lower weights.
Access works through two main routes: NHS weight loss medication is available through specialist tier 3 weight management services—you'll need a referral from your GP, though availability and waiting times vary significantly by region. Alternatively, you can access prescription weight loss treatment privately through a UK-licensed prescriber following an online clinical assessment. Use our free GLP-1 weight loss calculator to see potential results at different doses, and check your personal BMI using the BMI calculator on this page to help guide your conversation with a healthcare professional.
Wegovy (semaglutide) offers once-weekly dosing with doses from 0.25 mg to 2.4 mg, making it straightforward to use. Mounjaro (tirzepatide) also uses once-weekly injection but has a unique dual-hormone mechanism, which clinical evidence suggests may lead to slightly greater weight loss for some people—though results vary widely between individuals. Saxenda (liraglutide) requires a daily injection, which some people find less convenient, but it's been available longer and has extensive real-world safety data.
The "best" weight loss injection depends on your individual health profile, preferences, and how your body responds. Your GP or prescriber will assess which option is most suitable for you. Common side effects include nausea, diarrhoea, and stomach discomfort—these often improve over time. It's important to understand that prescription weight loss injections work best alongside dietary changes and increased physical activity, not as a replacement for them. Track your progress using our free progress tracker to monitor both weight changes and how you feel on any medication.
- 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 is the best weight loss injection for me?
The best weight loss injection depends on your individual health, BMI, any weight-related conditions, and personal preferences. Wegovy suits those who prefer once-weekly dosing and simpler escalation, while Mounjaro's dual mechanism may suit some. Your prescriber will assess your suitability. Individual results vary significantly.
How much weight can I lose with weight loss injections?
Clinical trials show average weight loss of 14.9–21% of body weight depending on the medication and dose. However, individual results vary considerably. Weight loss is typically achieved alongside a reduced-calorie diet and increased physical activity. You won't lose weight without lifestyle changes.
Can I get weight loss injections on the NHS in the UK?
Yes, weight loss medications are available through NHS specialist tier 3 weight management services if you meet eligibility criteria (BMI ≥30 or ≥27 with comorbidities). Access and waiting times vary significantly by region. Ask your GP about referral options in your area.
Are weight loss injections safe long-term?
GLP-1 medications have been used for type 2 diabetes for over 20 years, providing long-term safety data. However, they carry side effects including nausea, diarrhoea, and pancreatitis risk (rare). Always discuss risks and benefits with your prescriber before starting.
What happens when I stop taking weight loss injections?
Weight loss injections are typically used as ongoing treatment. Some weight regain may occur after stopping, particularly without sustained lifestyle changes. Your prescriber will discuss long-term management options and how to maintain results through diet and exercise.
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.