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
How Do Weight Loss Injections Work?
Weight loss injections available in the UK are prescription-only medicines that work by mimicking natural hormones to help reduce appetite and support weight management. These medications, licensed for adults with a BMI of 30 or above (or 27+ with weight-related health conditions), are typically used alongside diet and exercise changes. Understanding how they work, who is eligible, and what options are available through the NHS or private prescribing can help you decide whether this approach is right for you. Use our free GLP-1 weight loss calculator to explore potential outcomes if you meet eligibility criteria.
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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 and How They Work
Three prescription weight loss medications are currently licensed in the UK: Mounjaro (tirzepatide), Wegovy (semaglutide), and Saxenda (liraglutide). All work by activating natural hormone pathways in the gut and brain that regulate appetite and fullness.
Mounjaro is a dual GIP and GLP-1 receptor agonist — it activates two pathways simultaneously, helping reduce food cravings and slow gastric emptying. Wegovy is a single GLP-1 receptor agonist with a similar effect but through one pathway. Saxenda is also GLP-1 but administered as a daily injection rather than weekly.
In clinical trials, these medicines helped participants lose an average of 15–21% of body weight over several months when combined with a reduced-calorie diet and increased physical activity. Individual results vary significantly. They do not work as appetite suppressants in the traditional sense — they help regulate the brain's hunger signals and make you feel fuller after smaller meals.
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 and Eligibility
In the UK, weight loss injections are available through two routes: NHS specialist weight management services and private prescribing from GPhC-registered online clinics.
NHS access: You can be referred to a tier 3 or tier 4 specialist weight management service by your GP if you have a BMI of 30+ or 27+ with weight-related health conditions (such as type 2 diabetes, high blood pressure, or sleep apnoea). However, NHS availability varies significantly by region and waiting lists can be lengthy.
Private access: Available through licensed online prescribers following an online clinical assessment. No NHS referral is needed, but you pay privately. To find out whether you're eligible, your GP can discuss your individual situation, or you can have a confidential online assessment. Either way, a prescriber must assess your health before any medication is prescribed.
- 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 a GLP-1 weight loss injection and how does it differ from Mounjaro?
GLP-1 stands for glucagon-like peptide-1, a natural hormone that signals fullness to your brain. GLP-1 injections like Wegovy activate this single pathway. Mounjaro is different — it's a dual GIP/GLP-1 agonist, activating two pathways at once, which may explain why some clinical trials showed slightly higher average weight loss with Mounjaro compared to GLP-1-only options.
How quickly will I see weight loss results with prescription weight loss injections?
Weight loss typically begins within the first 2–4 weeks, but results vary considerably between individuals. Clinical trials showed average weight loss of 15–21% over 68 weeks when combined with diet and exercise. Some people lose more, others less. Sustainable weight loss is usually 0.5–1 kg per week. Your prescriber can discuss realistic timelines for your situation.
Are weight loss injections available on the NHS in my area?
NHS access to weight loss injections depends on your local integrated care board (ICB) and specialist weight management service availability. Your GP can refer you to your local tier 3 service if you're eligible (BMI 30+, or 27+ with weight-related conditions). However, waiting lists vary — some areas have months-long waits. Ask your GP about current availability in your area.
Do I need to be overweight or obese to get a weight loss injection in the UK?
To be eligible for prescription weight loss medication in the UK, you need a BMI of 30 kg/m² or above, or a BMI of 27–29.9 if you have at least one weight-related health condition such as type 2 diabetes, hypertension, or sleep apnoea. Use our free BMI calculator to check your current BMI and discuss eligibility with your GP.
What happens if I stop taking weight loss injections?
Weight management requires ongoing effort. If you stop taking weight loss injections without maintaining dietary and exercise changes, weight tends to return over time. This is why these medications are best viewed as part of a long-term lifestyle approach. Your prescriber can discuss the duration of treatment that's right 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.