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
Best Diet Pills 2025 — What Works in the UK
If you're searching for the best diet pills in 2025, it's important to understand that the most effective weight loss medications available in the UK are prescription-only drugs, not over-the-counter pills. The most clinically studied options are GLP-1 receptor agonist medications like Wegovy (semaglutide) and Mounjaro (tirzepatide), both licensed for weight management in UK adults. Unlike traditional diet pills, these medications work by reducing appetite and helping you feel fuller after smaller meals. Weight loss methods in the UK have evolved significantly, and prescription medications now form part of a comprehensive approach alongside sustainable lifestyle changes and dietary modifications.
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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 Prescription Weight Loss Medications Work
The term "diet pills" often refers to older, less effective medications, but modern prescription weight loss medications operate through a different mechanism. Wegovy (semaglutide) is a GLP-1 receptor agonist — a once-weekly injection that activates the natural hormone GLP-1, which signals fullness to your brain and slows how quickly food leaves your stomach. Mounjaro (tirzepatide) works similarly but activates two hormone pathways (GIP and GLP-1), which may provide additional support. Clinical trials showed Wegovy users lost an average of around 15% of their body weight, whilst Mounjaro users lost between 15–21% on average — though individual results vary significantly. These medications are only available on prescription following a clinical assessment, and they work best alongside a reduced-calorie diet and increased physical activity.
For sustainable weight loss in the UK, your GP can assess whether prescription medication is appropriate for you. Calculate your BMI instantly using our free BMI calculator above to understand your starting point and whether you may be eligible for treatment.
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 Weight Management and Getting Started
Access to prescription weight loss medications in the UK can come through two routes: NHS weight management programmes through specialist tier 3 services, or private prescribing via online assessment. The NHS weight loss programme typically requires referral from your GP to a specialist weight management service, though availability and waiting times vary significantly by region. Alternatively, private UK-licensed prescribers can assess your eligibility and issue a prescription if appropriate. Both routes require a clinical assessment to confirm you meet eligibility criteria — typically a BMI of 30 or above, or 27–29.9 with weight-related health conditions like type 2 diabetes or high blood pressure. Our free GLP-1 weight loss calculator can help you explore potential outcomes at different dose levels, whilst our weight converter and progress tracker support you in planning and monitoring your weight loss journey safely.
- 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.
What is the safest weight loss method in the UK?
The safest approach combines moderate calorie reduction (around 500 kcal/day deficit), increased physical activity, and professional support. The NHS recommends losing 0.5–1 kg per week. For eligible adults, prescription medications like Wegovy or Mounjaro, used alongside lifestyle changes, offer clinical evidence of safety and effectiveness when prescribed after proper assessment.
Are GLP-1 medications like Wegovy available on the NHS?
Yes, GLP-1 medications including Wegovy are available through NHS specialist weight management services for eligible patients. However, access varies by region and often involves waiting lists. Private prescription is also available through online clinical assessment with UK-licensed prescribers, typically at a cost of £129–£320 per month depending on dose.
What is the difference between Wegovy and Ozempic?
Both contain semaglutide, but Wegovy is specifically licensed for weight management and uses doses up to 2.4 mg weekly. Ozempic is licensed for type 2 diabetes (up to 2 mg) and using it for weight loss is off-label. Always ask your prescriber whether you are being prescribed the correct licensed version for your intended use.
How long do I need to take weight loss medication?
Weight loss medications are typically taken long-term whilst they are working and benefiting your health. Clinical guidelines suggest continuing as long as the medication is helping and side effects remain tolerable. Stopping medication often leads to weight regain, so ongoing use with lifestyle support is usually recommended.
Can I lose weight without prescription medication?
Yes. Many people lose weight through calorie deficit, increased activity, and behaviour change alone. NHS weight loss programmes, including the free digital NHS Weight Loss Plan and community programmes, provide structured support. Prescription medication is an option for those who need additional help or who meet clinical eligibility criteria.
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.