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
What Is The Best Weight Loss Injection In The UK?
There is no single "best" weight loss injection for everyone — eligibility and suitability depend on your individual health, BMI, and medical history. However, three prescription weight management injections are currently licensed in the UK: Mounjaro (tirzepatide), Wegovy (semaglutide), and Saxenda (liraglutide). All three are available through either NHS specialist services or private prescription. This guide explains how each works, what the clinical evidence shows, who can access them, and how to find out if prescription weight loss medication is right for you. Our free BMI calculator can help you understand your starting point, and our GLP-1 weight loss calculator can show potential outcomes based on different medications and doses.
10,000+ calculations today · NHS-aligned thresholds · 100% free
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-Licensed Weight Loss Injections — Your Options
Three prescription weight loss injections are currently licensed in the UK:
- Mounjaro (tirzepatide) — A once-weekly dual GIP and GLP-1 receptor agonist. Clinical trials showed average weight loss of 15–21% body weight over 72 weeks when used alongside a reduced-calorie diet and increased physical activity. Maximum dose is 15 mg weekly.
- Wegovy (semaglutide) — A once-weekly GLP-1 receptor agonist. STEP trials demonstrated average weight loss of approximately 15% body weight over 68 weeks. Maximum dose is 2.4 mg weekly.
- Saxenda (liraglutide) — A once-daily GLP-1 receptor agonist injection. Clinical evidence supports average weight loss of 5–8% body weight. Maximum dose is 3 mg daily.
All three work by activating natural hormone pathways that regulate appetite, reduce food cravings, and support feeling fuller after smaller meals. Individual results vary significantly based on diet, activity level, genetics, and baseline weight. A prescriber will assess which medication is most appropriate for you following a clinical consultation.
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 vs Private Access — How To Get Started
NHS access: NICE has approved tirzepatide (Mounjaro) for use within NHS specialist weight management services. You can ask your GP for a referral to your local tier 3 weight management service. However, NHS access varies significantly by region and waiting lists can be lengthy.
Private access: All three medications are available through GPhC-registered online pharmacies following an online clinical assessment with a UK-licensed prescriber. This route does not require an NHS referral. Typical costs range from £129–£320 per month depending on medication and dose.
Eligibility: You may be eligible if your BMI is 30 or above, or 27–29.9 with weight-related health conditions (type 2 diabetes, high blood pressure, cardiovascular disease, or sleep apnoea). Lower BMI thresholds apply if you're of South Asian, Chinese, Black African, or Black Caribbean heritage. Your prescriber will assess your full health history before any prescription is issued.
- 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 Mounjaro and Wegovy?
Both are once-weekly injections. Mounjaro (tirzepatide) is a dual GIP and GLP-1 agonist with average weight loss around 15–21%. Wegovy (semaglutide) is a GLP-1 agonist only with average weight loss around 15%. Both require clinical assessment. Results vary between individuals and depend on diet, activity, and adherence.
Can I get weight loss injections on the NHS?
Yes, through NHS specialist weight management services. NICE approved Mounjaro for NHS use. Your GP can refer you to your local tier 3 service, though availability and waiting times vary by region. Private prescription is also available without NHS referral through online prescribers.
How quickly will I lose weight on these injections?
The NHS recommends losing 0.5–1 kg per week for sustainable results. Most people see gradual changes over weeks 4–12 as doses are increased. Average weight loss is 15–21% body weight over 68–72 weeks in clinical trials, but this includes significant lifestyle changes. Individual results vary considerably.
Are weight loss injections safe?
All three medications are licensed and have undergone clinical trials in the UK. Common side effects include nausea, diarrhoea, and constipation — these often improve over time. Serious side effects are rare but can include pancreatitis. Your prescriber will assess whether the medication is safe for you based on your medical history.
What happens when I stop taking the injection?
Weight loss injections work alongside diet and physical activity changes. When you stop, weight loss typically plateaus and may reverse if lifestyle changes are not maintained. This is why they are most effective when combined with long-term dietary and activity modifications. Your prescriber can discuss sustainability with 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.