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 Is Diet Medication in the UK?
Diet medication refers to prescription-only medicines prescribed to support weight management in UK adults. The most commonly prescribed options are GLP-1 receptor agonist injections like Wegovy (semaglutide) and Mounjaro (tirzepatide), which work by regulating appetite and helping you feel fuller after smaller meals. These medications are only available through NHS specialist weight management services or private clinical assessment, and are always used alongside a reduced-calorie diet and increased physical activity for best results.
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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 Medication Works
Diet medications prescribed in the UK work by targeting hormones that control hunger and fullness. Wegovy (semaglutide) is a GLP-1 receptor agonist — it mimics a natural gut hormone that signals to your brain when you are satisfied. This may help reduce food cravings, support portion control, and slow how quickly food leaves your stomach. Mounjaro (tirzepatide) is a dual GIP and GLP-1 agonist, activating two appetite-regulation pathways for potentially greater effect.
Both are injected once weekly and are prescription-only, meaning you cannot access them without a clinical assessment from a UK-licensed prescriber. They are not appetite suppressants in the traditional sense — they work with your body's natural hormonal systems. In clinical trials, patients using these medications alongside lifestyle changes lost an average of 14–21% of their body weight, though individual results vary significantly.
These medications are typically prescribed as part of a comprehensive weight management plan through NHS tier 3 specialist services or private prescribing pathways. They require ongoing monitoring by a healthcare professional.
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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.
Eligibility and NHS Access in the UK
In the UK, you may be eligible for prescription diet medication 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 cardiovascular disease. For adults of South Asian, Chinese, Black African, or Black Caribbean heritage, lower BMI thresholds apply — eligibility may start at BMI 27.5 or above, as these groups face higher health risks at lower weights.
NHS access requires referral to a specialist weight management service (tier 3), which can involve significant waiting lists in many regions. Private prescribing is available without NHS referral through online consultations with UK-licensed prescribers, though this involves a cost. Your GP can advise on both pathways and assess whether diet medication is appropriate for you based on your individual health. Use our free BMI calculator above to check where your weight falls on NHS guidelines, and our GLP-1 weight loss calculator to see potential outcomes with medication.
- 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.
Is diet medication the same as an appetite suppressant?
Not exactly. Diet medications like Wegovy and Mounjaro work by mimicking natural hormones that regulate hunger and fullness, rather than simply suppressing appetite. They help you feel satisfied on smaller portions and may reduce food cravings, but they work with your body's systems rather than forcing appetite loss.
Can I get diet medication from my GP?
In most cases, no. Diet medications are typically prescribed through NHS specialist tier 3 weight management services following referral from your GP, not directly by your GP surgery. Private prescribing is available through online consultations with UK-licensed prescribers. Your GP can discuss both options and help you decide which pathway is right for you.
How much weight will I lose with diet medication?
Clinical trials show an average loss of 14–21% of body weight over 68 weeks when using GLP-1 medications alongside a reduced-calorie diet and increased activity. However, individual results vary significantly — some people lose more, some less. Results depend on adherence, lifestyle changes, dose, and individual metabolism. Our weight loss calculator can help estimate potential outcomes.
Are diet medications safe long-term?
GLP-1 and GIP/GLP-1 medications have been studied in long-term clinical trials and are considered safe for ongoing use when prescribed by a qualified healthcare professional. However, they do have side effects (commonly nausea and digestive changes) that some people find difficult to tolerate. Your prescriber will monitor your health regularly.
What happens when I stop taking diet medication?
Weight may return over time if lifestyle changes are not maintained. Diet medications are tools to support weight loss, not permanent solutions — they work best when combined with sustainable dietary changes and increased physical activity. Discuss long-term plans with your prescriber before stopping any medication.
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.