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
Which Weight Loss Injection Is Best for You?
There is no single "best" weight loss injection — the right medication depends on your individual health, BMI, eligibility, and how your body responds. Three prescription weight management injections are currently licensed in the UK: Mounjaro (tirzepatide), Wegovy (semaglutide), and Saxenda (liraglutide). All three have clinical evidence supporting their use for weight loss uk, but they work differently and suit different people. This guide explains how each works, what the evidence shows, and how to find out which option might be right for you.
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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-Licensed Weight Loss Injections: What's Available
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist — it activates two hormone pathways to help reduce appetite and support feeling fuller after smaller meals. In clinical trials, Mounjaro users lost an average of 15–21% of their body weight over 72 weeks when combined with diet and exercise changes.
Wegovy (semaglutide) is a GLP-1 receptor agonist that activates one hormone pathway. Clinical trial data showed users lost approximately 14.9% of body weight at 68 weeks on the maximum dose (2.4 mg weekly).
Saxenda (liraglutide) is also a GLP-1 agonist but given as a daily injection (not weekly). Average weight loss in trials was around 5–10% of body weight, with lower average outcomes compared to Mounjaro and Wegovy.
The key difference: Mounjaro's dual mechanism may produce slightly higher weight loss on average, though individual results vary significantly. Your GP or prescriber will assess which suits your health profile best.
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
In the UK, prescription weight loss medication is accessed through two routes:
- NHS: Via referral to a tier 3 specialist weight management service. Eligibility typically requires a BMI of 30 or above, or 27–29.9 with weight-related health conditions (such as type 2 diabetes or high blood pressure). NHS access varies significantly by region and waiting times can be lengthy.
- Private: Through an online consultation with a UK-licensed prescriber, who will assess your eligibility and issue a prescription if appropriate. Available without NHS referral.
Start by speaking to your GP about your weight loss goals. They can assess your eligibility, discuss which medication might suit you, and explain NHS options in your area. Use our free BMI calculator above to check your current BMI — this helps you understand whether you meet eligibility thresholds. Your GP can also refer you to NHS weight management services if available locally.
- 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.
Can I choose between Mounjaro, Wegovy, and Saxenda?
Your prescriber will recommend the most suitable medication based on your health profile, medical history, and preferences. Mounjaro and Wegovy are more commonly prescribed than Saxenda due to higher average weight loss outcomes in clinical trials. You can discuss options with your GP or prescriber, but the final choice is clinical.
Which weight loss injection works fastest?
Weight loss typically begins within weeks of starting, but most significant loss occurs over months 3–12. Mounjaro may produce faster average weight loss than Wegovy or Saxenda based on clinical trials, but individual responses vary widely. Sustainable weight loss requires combining medication with diet and exercise changes.
How much weight will I lose on a weight loss injection?
Average results from clinical trials: Mounjaro ~15–21% body weight, Wegovy ~14.9%, Saxenda ~5–10%. However, individual outcomes vary significantly. Someone might lose more or less than average. Our GLP-1 weight loss calculator can help estimate potential weight loss based on different doses — though actual results depend on your lifestyle, metabolism, and adherence.
Do I need to be obese to get a weight loss injection in the UK?
No. UK eligibility includes adults with a BMI of 30 or above, OR a BMI of 27–29.9 with weight-related health conditions like type 2 diabetes, high blood pressure, or sleep apnoea. Lower BMI thresholds may apply if you are of South Asian, Chinese, Black African, or Black Caribbean heritage. Your GP can assess your individual eligibility.
What happens if a weight loss injection doesn't work for me?
If one medication is not producing results after several weeks at therapeutic dose, your prescriber may suggest switching to another option or adjusting your dose. Some people respond better to Mounjaro's dual mechanism, while others do equally well on Wegovy. Lifestyle changes alongside medication are essential — if diet and exercise haven't changed, weight loss is unlikely regardless of injection type.
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.