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 Is a Dieting Injection? UK Health Guide
Dieting injections, commonly called weight loss jabs or slimming injections, are prescription-only medications that help support weight management in UK adults. These injectable medicines work by affecting appetite and food intake, and are prescribed alongside diet and exercise changes. In the UK, they're available through NHS specialist services or private prescribing, with eligibility based on BMI and health factors. This guide explains how they work, who can access them, and what to expect.
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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 Dieting Injections Work in UK Adults
Dieting injections licensed in the UK are GLP-1 receptor agonists or GIP/GLP-1 dual agonists — medications that mimic natural hormones your body produces after eating. These hormones signal fullness to your brain, slow how quickly food leaves your stomach, and help regulate blood sugar levels.
The main licensed dieting injections available in the UK are:
- Mounjaro (tirzepatide) — a once-weekly injection that activates both GIP and GLP-1 pathways
- Wegovy (semaglutide) — a once-weekly GLP-1 injection
- Saxenda (liraglutide) — a daily GLP-1 injection
Clinical trials showed that adults using these medications alongside a reduced-calorie diet and increased physical activity lost an average of 15–21% of their body weight — though individual results vary significantly. These are prescription-only medicines requiring clinical assessment before being prescribed.
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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.
UK Eligibility and NHS Access for Weight Loss Injections
In the UK, you may be eligible for a prescription dieting injection if you have a BMI of 30 or above, or a BMI of 27–29.9 with weight-related health conditions such as type 2 diabetes, high blood pressure, or heart disease.
For people of South Asian, Chinese, Black African, or Black Caribbean heritage, eligibility thresholds are slightly lower due to higher health risks at lower BMI levels. NHS access is through specialist tier 3 weight management services (referral from your GP), though waiting lists vary by region. Private prescribing is also available through GPhC-registered online services. Your GP or a licensed prescriber can assess your individual suitability and discuss whether a dieting injection is appropriate for your circumstances.
- 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 dieting injections available on the NHS in the UK?
Yes. NICE has approved tirzepatide (Mounjaro) and semaglutide (Wegovy) for NHS use within specialist weight management services. Access is through tier 3 services via GP referral. Availability and waiting times vary significantly by region. Private prescribing is also available without NHS referral.
How much weight can you lose with a dieting injection?
Clinical trials showed average weight losses of 15–21% of body weight over 68–72 weeks when combined with a reduced-calorie diet and exercise. However, results vary between individuals. Some people lose more, others less. A prescriber can help estimate realistic outcomes based on your individual health.
What are the side effects of UK dieting injections?
Common side effects include nausea, diarrhoea, constipation, and stomach pain. These usually improve over time as your body adjusts. Serious side effects are rare but may include severe stomach pain (possible pancreatitis) or gallbladder problems. Always report any concerning symptoms to your GP or prescriber immediately.
Can you get a dieting injection prescription from your GP?
Most GPs do not prescribe dieting injections directly. You'll typically need referral to a specialist weight management service (tier 3) through your GP, or you can access private prescribing through an online licensed prescriber following a clinical assessment. This ensures the medication is appropriate for your individual health.
How do I know if a dieting injection is right for me?
Start by calculating your BMI using our free BMI calculator above to see if you meet the eligibility threshold. Check your weight against NHS healthy weight ranges using our weight converter for UK measurements. Then discuss options with your GP or a licensed prescriber, who will assess your health history, current medications, and weight loss goals to determine suitability.
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.