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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What Are Diet Jabs? UK Health Guide
Diet jabs — commonly called weight loss injections or slimming jabs — are prescription medications designed to help manage weight in UK adults. These injectable medicines work by mimicking natural hormones that regulate appetite and blood sugar. They're only available on prescription following a clinical assessment, and are used alongside healthy lifestyle changes. This guide explains how they work, who can access them through the NHS or privately, and what you should know before considering this weight management option.
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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 Diet Jabs Work and UK Eligibility
Diet jabs are GLP-1 or GIP/GLP-1 receptor agonist medications — they mimic natural hormones your body produces to regulate appetite, fullness signals, and blood sugar. The two main options licensed in the UK are Mounjaro (tirzepatide) and Wegovy (semaglutide). Both are once-weekly injections given at home.
In the UK, you may be eligible if you have a BMI of 30 or above, or 27–29.9 with weight-related health conditions such as type 2 diabetes, high blood pressure, or heart disease. For adults of South Asian, Chinese, Black African, or Black Caribbean heritage, lower BMI thresholds apply due to higher health risks at lower weights.
These are prescription-only medicines. Access through the NHS is via specialist tier 3 weight management services (availability varies by region). Private access is available through GPhC-registered online pharmacies following an online clinical assessment. Use our free GLP-1 weight loss calculator to estimate potential weight loss at different doses alongside diet and exercise.
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 Access and What the Evidence Shows
NHS access to diet jabs has improved following NICE approval of tirzepatide (Mounjaro). However, availability remains limited and regional waiting lists can be long. Your GP can refer you to local specialist weight management services, but many areas have lengthy waiting periods.
Clinical trials show diet jabs may help with significant weight loss — on average, 15–21% of body weight with Mounjaro and around 15% with Wegovy — though individual results vary considerably. Results are achieved alongside reduced-calorie diet and increased physical activity. Common side effects include nausea, constipation, and diarrhoea, typically mild and reducing over time. Before considering diet jabs, use our BMI calculator to understand your current health status and discuss options with your GP.
- 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 diet jabs available on the NHS in the UK?
Yes, Mounjaro and Wegovy are approved for NHS use through specialist weight management services. However, access varies by region and waiting lists can be very long. Your GP can refer you to local tier 3 services. Private access is also available through UK-registered online pharmacies following clinical assessment.
Who can get diet jabs in the UK?
Adults with a BMI of 30 or above, or 27–29.9 with weight-related health conditions (type 2 diabetes, high blood pressure, cardiovascular disease) may be eligible. Lower BMI thresholds apply for South Asian, Chinese, Black African, and Black Caribbean adults. You must be assessed by a licensed prescriber.
What's the difference between Mounjaro and Wegovy?
Both are GLP-1 weight loss injections. Mounjaro (tirzepatide) is a dual GIP and GLP-1 agonist with a maximum dose of 15mg. Wegovy (semaglutide) is a GLP-1 agonist with a maximum dose of 2.4mg. Clinical trials show similar weight loss results, though individual outcomes vary.
How much weight can you lose with diet jabs?
On average, clinical trials show weight loss of 15–21% of body weight with Mounjaro and around 15% with Wegovy over 68 weeks. Results are achieved alongside diet and exercise changes. Individual results vary significantly — some people lose more, some less. Your prescriber can discuss realistic expectations.
What are the side effects of diet jabs?
Common side effects include nausea, constipation, diarrhoea, and abdominal pain — usually mild and improving over time. Serious side effects are rare but include severe stomach pain (possible pancreatitis) and gallbladder issues. Always report unexpected symptoms to your GP or 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.