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
Prescription Weight Loss Injections in the UK
Prescription weight loss injections are licensed medications that may help adults manage excess weight when combined with diet and physical activity. In the UK, several injectable medications are available on prescription, including semaglutide (Wegovy) and tirzepatide (Mounjaro). These GLP-1 and GLP-1/GIP receptor agonist medications work by reducing appetite and helping you feel fuller after smaller meals. Access is available through the NHS specialist weight management services or privately through online clinical assessments. Individual results vary, and all these medications require a prescription from a qualified healthcare professional following a thorough health assessment.
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.
How Prescription Weight Loss Injections Work
Prescription weight loss injections are receptor agonist medications that activate natural hormone pathways in your body. The most commonly prescribed options in the UK are:
- Wegovy (semaglutide) — a once-weekly GLP-1 injection with clinical trials showing average weight loss of around 15% of body weight
- Mounjaro (tirzepatide) — a once-weekly dual GIP/GLP-1 injection with clinical trials showing average weight loss of 15–21% of body weight
- Saxenda (liraglutide) — a once-daily GLP-1 injection option
These medications slow how quickly food leaves your stomach, reduce appetite signals to your brain, and help regulate blood sugar. They are prescribed as part of weight management uk approaches that combine medication with reduced-calorie diet and increased physical activity. Important: results vary significantly between individuals, and these are prescription-only medicines requiring clinical assessment before being prescribed.
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.
UK Eligibility and How to Access
You may be eligible for prescription weight loss medication in the UK if you have a BMI of 30 or above, or 27 or above with weight-related health conditions such as type 2 diabetes, 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 routes include NHS specialist weight management services (referral via your GP, though waiting lists vary by region) or private prescription through an online clinical assessment with a UK-licensed prescriber. Our free GLP-1 weight loss calculator can help you estimate potential outcomes at different doses. Your GP or prescriber will assess whether this treatment is suitable for your individual health profile.
- 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 Wegovy and Ozempic?
Both contain semaglutide, but Wegovy is specifically licensed for weight management at doses up to 2.4mg, while Ozempic is approved for type 2 diabetes management at lower doses. Using Ozempic for weight loss is off-label; Wegovy is the licensed UK weight loss option. Your prescriber can advise which is appropriate for you.
How much weight will I lose on prescription weight loss injections?
Clinical trials show average weight loss of 15–21% of body weight, but individual results vary significantly. Some people lose more, some less. Results depend on your starting weight, adherence to the medication schedule, dietary changes, and physical activity. Your progress tracker can help monitor your personal results.
Are prescription weight loss injections available on the NHS?
Yes, tirzepatide (Mounjaro) and semaglutide (Wegovy) are approved for NHS use within specialist tier 3 weight management services. However, availability and waiting times vary significantly by region and NHS integrated care board. Your GP can refer you to your local service, though waiting lists may be lengthy.
What are the main side effects of prescription weight loss injections?
Common side effects include nausea, diarrhoea, constipation, and stomach pain—particularly when starting or increasing doses. Most improve over time. Serious side effects are rare but can include severe stomach pain (possible pancreatitis) or gallbladder problems. Always report any concerning symptoms to your prescriber immediately.
Do I need to change my diet and exercise when taking prescription weight loss medication?
Yes. Prescription weight loss injections work best alongside a reduced-calorie diet and increased physical activity. They are not a replacement for lifestyle changes. NHS weight loss guidance recommends losing 0.5–1kg per week for sustainable results combined with healthier eating and regular movement.
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.