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
What Are Diet Injections in the UK?
Diet injections, commonly called slimming injections or weight loss jabs in the UK, are prescription-only medicines designed to help with weight management. Unlike cosmetic injections, these are medical treatments that work by affecting how your body regulates appetite and fullness. Three medications are currently licensed for weight loss in the UK: Mounjaro (tirzepatide), Wegovy (semaglutide), and Saxenda (liraglutide). All require a prescription following a clinical assessment, and all work alongside reduced-calorie diets and increased physical activity for best results.
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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.
UK-Licensed Weight Loss Injections
Three prescription slimming injections are currently available in the UK for weight management:
- Mounjaro (tirzepatide) — a dual GIP and GLP-1 receptor agonist administered once weekly. Clinical trials showed participants lost an average of 15–21% of their body weight, though individual results vary significantly.
- Wegovy (semaglutide) — a GLP-1 receptor agonist given once weekly. In trials, average weight loss was approximately 15% of body weight alongside lifestyle changes.
- Saxenda (liraglutide) — a GLP-1 agonist given as a daily injection. It has been available in the UK longer than Mounjaro or Wegovy and supports similar weight management goals.
All three medications are prescription-only and require assessment by a GP or licensed prescriber to determine suitability. Access varies — some are available through NHS tier 3 specialist weight management services, whilst others are available privately through GPhC-registered online prescribing services. Try our free GLP-1 weight loss calculator to understand how these medications might support your individual weight management journey.
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.
How Do Weight Loss Injections Work?
GLP-1 receptor agonists work by mimicking a natural hormone your gut produces after eating. This hormone signals to your brain that you are full, helping reduce appetite and food cravings. The injections slow how quickly food leaves your stomach, allowing you to feel satisfied with smaller meals. Mounjaro works slightly differently — it activates two hormone pathways (GIP and GLP-1) rather than one, which may explain its slightly stronger effects in some people. These are not appetite suppressants in the traditional sense; they support your body's natural fullness signals. Weight loss results are best when combined with a reduced-calorie diet and regular physical activity. Individual results vary considerably — some people experience significant weight loss, whilst others see more modest changes.
- 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 injections the same as cosmetic injections?
No. Diet injections (weight loss jabs) are prescription medicines that affect appetite hormones and are taken internally under the skin. Cosmetic injections are aesthetic treatments. Weight loss injections require clinical assessment and are only available on prescription from a UK healthcare provider.
How often do you need diet injection injections?
Mounjaro and Wegovy are once-weekly injections. Saxenda is a daily injection. Each requires a prescription and ongoing monitoring by your prescriber. Missing doses or stopping suddenly may affect results.
Can I get weight loss injections on the NHS?
Access varies by region. Some NHS tier 3 specialist weight management services offer Mounjaro or Wegovy, but availability is limited and waiting lists can be long. Private online prescribing services also offer these medications following clinical assessment. Your GP can discuss your options.
What weight do I need to be to get diet injections?
Generally, you need a BMI of 30 or above (obesity), or a BMI of 27–29.9 with weight-related health conditions like type 2 diabetes or high blood pressure. Use our free BMI calculator to check your personal BMI. South Asian and other ethnic groups may qualify at lower BMI levels due to higher health risks.
Do diet injections work without diet and exercise?
No. These medications are most effective alongside a reduced-calorie diet and increased physical activity. They support your weight management efforts but are not standalone treatments. Your prescriber will discuss lifestyle changes as part of your treatment plan.
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.