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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Weight Loss Injections in the UK — Your Guide
Weight loss injections are prescription-only medicines available in the UK through both NHS specialist services and private online prescribing. The most commonly prescribed options are Wegovy (semaglutide) and Mounjaro (tirzepatide), both licensed for weight management. These are GLP-1 and GLP-1/GIP medications that work by helping regulate appetite and blood sugar. Eligibility depends on your BMI and health conditions. This guide explains how to access them, what to expect, and whether they might be suitable for you.
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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 and What They Are
Weight loss injections are prescription-only medicines that use two main types of medication: GLP-1 receptor agonists and GIP/GLP-1 receptor agonists. Wegovy (semaglutide) is a once-weekly GLP-1 injection licensed in the UK for weight management. Mounjaro (tirzepatide) is also a once-weekly injection but activates both GIP and GLP-1 pathways, which may enhance appetite regulation.
In clinical trials, these medications helped participants lose an average of 15–21% of their body weight, though individual results vary significantly. They work by:
- Reducing appetite and food cravings
- Helping you feel fuller after smaller meals
- Slowing how quickly food leaves your stomach
- Supporting better blood sugar control
Important: These are not insulin and are not cosmetic injections. They are serious prescription medications that require ongoing clinical assessment. Use our free GLP-1 weight loss calculator to estimate potential weight loss at different doses.
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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 Weight Loss Injections
To be eligible for prescription weight loss injections in the UK, you typically need:
- A BMI of 30 kg/m² or above, OR
- A BMI of 27–29.9 kg/m² with weight-related health conditions (type 2 diabetes, high blood pressure, heart disease, sleep apnoea)
- For South Asian, Chinese, Black African, or Black Caribbean adults: lower thresholds may apply due to higher health risks at lower BMI
Access routes: Through NHS tier 3 specialist weight management services (via GP referral, often with waiting lists) or private online prescribing (following an online clinical assessment with a UK-licensed prescriber). Check your BMI using our free BMI calculator to see where you fall on the eligibility spectrum.
- 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.
Are weight loss injections available on the NHS?
Yes, tirzepatide (Mounjaro) and semaglutide (Wegovy) are approved for NHS use through specialist tier 3 weight management services. However, availability varies by region, and waiting lists can be long. Your GP can refer you to your local specialist service. Private prescribing is also available without an NHS referral.
What's the difference between Wegovy and Ozempic?
Both contain semaglutide, but Wegovy is licensed specifically for weight management (up to 2.4 mg weekly dose). Ozempic is approved for type 2 diabetes management at lower doses and is not licensed for weight loss in the UK. Using Ozempic for weight loss would be off-label use.
How much weight can I expect to lose with these injections?
Clinical trials show average weight loss of 15–21% of body weight over 68–72 weeks, alongside diet and exercise. However, results vary considerably between individuals. Some people lose more, others less. Weight loss is not assured. Your prescriber can discuss realistic expectations for you.
Do I need to change my diet and exercise when using weight loss injections?
Yes. Weight loss injections work most effectively alongside a reduced-calorie diet and increased physical activity. They are not a substitute for lifestyle changes—they support your efforts by helping regulate appetite. A prescriber will discuss diet and exercise expectations with you.
What are the main side effects of 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 pancreatitis (severe stomach pain) and gallbladder problems. Always report concerns to your prescriber immediately.
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.