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 — What You Need to Know
Weight loss injections are prescription-only medications that may help support weight management when used alongside diet and exercise changes. In the UK, licensed options include Wegovy (semaglutide) and Mounjaro (tirzepatide), both GLP-1 or dual-mechanism receptor agonists. These are not available to buy directly from a UK pharmacy or other high street pharmacies without a prescription — you'll need a clinical assessment from a UK-licensed prescriber first. This guide explains how they work, what to expect, and how to access them safely through NHS or private routes.
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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.
How Weight Loss Injections Work and What Evidence Shows
Weight loss injections contain GLP-1 receptor agonist medications that mimic a natural hormone your body produces after eating. They work by signalling to your brain that you feel fuller, reducing food cravings, and slowing how quickly food leaves your stomach. Clinical trials have shown real results: the STEP-1 trial found that Wegovy (semaglutide) helped participants lose an average of approximately 15% of their body weight over 68 weeks, alongside a reduced-calorie diet and increased physical activity. Mounjaro (tirzepatide) is a dual GIP and GLP-1 agonist, which may have slightly different effects — average weight loss in trials was around 15–21% depending on dose. Individual results vary significantly. These injections are prescription-only and require a clinical assessment to check they're suitable for you. You can use our free GLP-1 weight loss calculator to explore potential weight loss projections at different doses.
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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.
Where to Get Weight Loss Injections — NHS and Private Options in the UK
NHS route: You can access weight loss medication through NHS specialist tier 3 or tier 4 weight management services if referred by your GP. Availability varies significantly by region, and waiting lists can be lengthy. Private route: You can obtain prescriptions through GPhC-registered online prescribing services following an online clinical assessment with a UK-licensed prescriber. These are then dispensed by UK pharmacies. Weight loss injections are not available to purchase directly from a UK pharmacy, a UK pharmacy, or other high street pharmacies without a valid prescription. Any legitimate supply requires a proper clinical assessment first. You can check your personal BMI using our free BMI calculator to understand where you fall on the NHS 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.
Can you buy weight loss injections from a UK pharmacy?
No. Weight loss injections are prescription-only medicines in the UK. a UK pharmacy and other high street pharmacies cannot supply them without a valid prescription from a UK-licensed prescriber. You'll need a clinical assessment first through either NHS specialist services or a private prescribing service.
What do people say about weight loss injections — are they effective?
Clinical trial data shows weight loss injections help participants lose 15–21% of body weight on average, alongside diet and exercise changes. Individual experiences vary. Common side effects reported include nausea, diarrhoea, and constipation, especially at the start of treatment. Results depend on dose, adherence, lifestyle changes, and individual metabolism.
How much do weight loss injections cost in the UK?
NHS access is free but requires referral to specialist services and varies by region. Private costs typically range from £129–£320 per month depending on the medication and dose. Mounjaro and Wegovy have different pricing structures based on the specific dose prescribed.
What's the difference between Wegovy and Mounjaro?
Wegovy (semaglutide) is a single GLP-1 agonist with a maximum dose of 2.4 mg weekly. Mounjaro (tirzepatide) is a dual GIP and GLP-1 agonist with a maximum dose of 15 mg weekly. Mounjaro may produce slightly higher average weight loss in trials, but individual results vary. Both require prescriptions and clinical assessment.
Are weight loss injections safe?
Prescription weight loss injections are licensed medicines with established safety profiles from clinical trials. However, they're not suitable for everyone — pregnancy, certain medical conditions, and other medications can be contraindications. A prescriber will assess your individual health before prescribing. Common side effects are usually temporary and manageable.
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.